1.	(a)	(i)	Define the terms:
atomic number ...............................................................................................
......................................................................................................................
mass number .................................................................................................
......................................................................................................................
(2)
 
(ii)	Identify the particle which contains 11 protons, 12 neutrons and 10 electrons.
......................................................................................................................
(1)
 
(b)	Bromine consists of two isotopes, mass numbers 79 and 81.  A sample of bromine gas, Br2, was examined in a mass spectrometer.  The mass spectrum showing the molecular ions is given below.

(i)	Identify the species responsible for the peak at m/e = 160.
......................................................................................................................
(1)

(ii)	Deduce the relative abundances of the two isotopes,

(2)
 
(c)	Define the term first electron affinity for bromine atoms, illustrating your answer with an equation.
................................................................................................................................
................................................................................................................................
................................................................................................................................
................................................................................................................................
(3)
 
(d)	The graph showing the variation of the first ionisation energies of the elements neon to potassium is given below.

(i)	Define the term first ionisation energy with reference to neon.
......................................................................................................................
......................................................................................................................
......................................................................................................................
(2)

(ii)	Explain the general trend in the first ionisation energies of the elements sodium to argon.
......................................................................................................................
......................................................................................................................
......................................................................................................................
(2)
 
(iii)	Explain why the first ionisation energy of neon is greater than the first ionisation energy of argon.
......................................................................................................................
......................................................................................................................
......................................................................................................................
(2)
(Total 15 marks)

2.	(a)	Iron has several isotopes. One of them has the electronic configuration [Ar]3d64s2 , an atomic number of 26 and a mass number of 56. 
(i)	Which of these pieces of information would be the most use in helping a chemist decide on the likely chemical reactions of iron?
............................................................................................................................
............................................................................................................................
(1)
(ii)	State how many of each of the following particles is found in an atom of 56Fe.
Protons ................         electrons ................            neutrons ................
(2)
 
(iii)	What are isotopes?
............................................................................................................................
............................................................................................................................
(2)

(b)	The relative atomic mass of a sample of iron may be found by using a mass spectrometer to determine the isotopic composition.
(i)	The diagram below represents a low-resolution mass spectrometer in which four areas have been identified. State what happens in each of these areas.

Area A ..............................................................................................................
Area B ..............................................................................................................
Area C ..............................................................................................................
Area D ..............................................................................................................
(4)
 
(ii)	In such a determination the following isotopic composition was found.
Isotope	Percentage composition	
54Fe	5.8	
56Fe	91.6	
57Fe	2.2	
58Fe	0.33	

	Calculate the relative atomic mass of this sample of iron, giving your answer to two decimal places.

(2)
(Total 11 marks)

3.	In the Periodic Table, where elements are arranged by atomic number, chlorine is a p-block element whereas manganese, a transition element, is in the d-block.
(a)	(i)	Define the term atomic number.
......................................................................................................................
......................................................................................................................
(1)
 
(ii)	Define the term d-block element
......................................................................................................................
......................................................................................................................
(1)
 
(iii)	Define the term transition element.
......................................................................................................................
......................................................................................................................
......................................................................................................................
(1)
 
(b)	The electron configuration of chlorine is 1s2 2s2 2p6 3s2 3p5. Write the electron configuration for manganese in a similar manner.
................................................................................................................................
(1)

(c)	(i)	Define the terrm first ionisation energy of chlorine.
......................................................................................................................
......................................................................................................................
......................................................................................................................
(2)
 
(ii)	Sketch the pattern you would expect to see in a plot of successive ionisation energies of chlorine against the number of electrons removed.

(3)

(d)	Manganese(IV) oxide, MnO2, reacts with concentrated hydrochloric acid to produce chlorine, water and a salt.  The salt has a composition of 43.7% manganese and 56.3% chlorine by mass.
Determine the empirical formula of the salt.

(3)
(Total 12 marks)

4.	(a)	When a sample of copper is analysed using a mass spectrometer, its atoms are ionised and then accelerated.
(i)	Explain how the atoms of the sample are ionised.
......................................................................................................................
......................................................................................................................
......................................................................................................................
(2)
 
(ii)	State how the resulting ions are then accelerated.
......................................................................................................................
......................................................................................................................
(1)

(b)	For a particular sample of copper two peaks were obtained in the mass spectrum.
Peak at m/e	Relative abundance	
63	69.1	
65	30.9	
(i)	Give the formula of the species responsible for the peak at m/e = 65.
......................................................................................................................
(1)
 
(ii)	State why two peaks, at m/e values of 63 and 65, were obtained in the mass spectrum.
......................................................................................................................
(1)
(iii)	Calculate the relative atomic mass of this sample of copper, using the table of results above.

(2)
(Total 7 marks)

5.	(a)	(i)	What is meant by the mass number of an atom?
..........................................................................................................................
(1)
 
(ii)	Define the term relative atomic mass.
..........................................................................................................................
(2)
 
(iii)	What are isotopes?
..........................................................................................................................
(2)
 
(b)	Magnesium has three isotopes. The mass spectrum of magnesium shows peaks at m/e 24 (78.60%), 25 (10.11%), and 26 (11.29%). Calculate the relative atomic mass of magnesium to 4 significant figures.

(2)
(Total 7 marks)

6.	(a)	Define the term first ionisation energy for magnesium. 
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
 
(b)	The logarithm of successive ionisation energies for magnesium is plotted in the graph below.

	Explain what this graph tells you about the electron arrangement in the magnesium atom.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
 
(c)	(i)	Give the full electronic configuration of magnesium using the s,p,d notation.
..........................................................................................................................
(1)
 
(ii)	Explain why all isotopes of magnesium have the same chemical properties.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(Total 9 marks)

7.	The table below shows the melting temperatures of the elements of period 3.

(a)	Write in the spaces in the table the structural type for these elements.
(2)

(b)	Explain why the melting temperature of sodium is so much lower than that of magnesium or of aluminium.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
 
(3)
(c)	(i)	Explain the very low melting temperature of argon.
..........................................................................................................................
..........................................................................................................................
(1)
 
(ii)	Phosphorus exists as P4, sulphur as S8. Explain the difference in the melting temperature of these substances.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(Total 8 marks)

8.	(a)	Complete the following table:
Particle	Relative charge	Relative mass	
Proton		1	
Electron	–1		
Neutron		1	
(3)

(b)	State the number of each of the above particles present in one molecule of CH4, showing clearly how you arrive at your answer.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
 
(c)	Complete the electronic configuration of a chlorine atom.
1s2 ............................................................................................................................
(1)
 
(d)	Give the formula of the chlorine species composed of 17 protons, 20 neutrons and 16 electrons.
....................................................................................................................................
(2)
 
(e)	Write one equation in each case to represent the change occurring when the following quantities are measured.
(i)	The first electron affinity of sulphur.
............................................................................................................................
(2)
 
(ii)	The first ionisation energy of sulphur.
........................................................................................................................
(1)

(f)	Explain why the first ionisation energy of chlorine is higher than that of sulphur.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(Total 14 marks)

9.	(a)	(i)	Complete the electronic configuration of calcium.
1s2 ....................................................................................................................
(1)
 
(ii)	State the number of electrons in the outer shell of an atom of chlorine.
………………………………………………………………………………..
(1)
 
(b)	(i)	Write the equation for the reaction of calcium with chlorine to produce calcium chloride.
………………………………………………………………………………..
(1)
 
(ii)	Name the type of bonding in calcium chloride.
………………………………………………………………………………..
(1)

(iii)	Draw a dot and cross diagram for calcium chloride showing all the outer electrons.

(3)
(Total 7 marks)

10.	(a)	State the number of protons, neutrons and electrons in a  ion.
	protons: ……………… 	neutrons: ………………	electrons: ………………
(3)
 
(b)	The mass spectrum of lithium shows two peaks. Their mass/charge ratios and percentage abundance are shown below.
Mass/charge	% Abundance	
6.02	7.39	
7.02	92.61	
 
	Calculate the relative atomic mass of lithium, giving your answer to three significant figures.

(2)

(c)	Describe a test that you would do to distinguish between solid lithium chloride and solid sodium chloride. Clearly state what you would do and what you would see with both substances.
………….…………………………………………………………………………….
………….…………………………………………………………………………….
………….…………………………………………………………………………….
………….…………………………………………………………………………….
(3)
(Total 8.marks)

11.	(a)	The first ionisation energy of potassium is +419 kJ mol–1 and that of sodium
is +496 kJ mol–1.
(i)	Define the term first ionisation energy.
………….……………….……………………………………………………..
………….……………….……………………………………………………..
………….……………….……………………………………………………..
(3)
 
(ii)	Explain why the first ionisation energy of potassium is only a little less than the first ionisation energy of sodium.
………….……………….……………………………………………………..
………….……………….……………………………………………………..
………….……………….……………………………………………………..
………….……………….……………………………………………………..
………….……………….……………………………………………………..
(3)

(b)	Potassium forms a superoxide, KO2. This reacts with carbon dioxide according to the equation:
4KO2(s) + 2CO2(g) ® 2K2CO3(s) + 3O2(g)
	Carbon dioxide gas was reacted with 4.56 g of potassium superoxide.
(i)	Calculate the amount, in moles, of KO2 in 4.56 g of potassium superoxide.

(2)
 
(ii)	Calculate the amount, in moles, of carbon dioxide that would react with 4.56 g of potassium superoxide.

(1)
 
(iii)	Calculate the volume of carbon dioxide, in dm3, that would react with 4.56 g of potassium superoxide. Assume that 1.00 mol of a gas occupies 24 dm3 under the conditions of the experiment.

(1)

(iv)	What volume of oxygen gas, in dm3, measured under the same conditions of pressure and temperature, would be released?

(1)
(Total 11 marks)

12.	A sample of titanium (atomic number 22) is made up of five isotopes. The sample has the following percentage composition:
Mass number
46
47
48
49
50	% composition
8.0
7.3
74.0
5.5
5.2	
 
(a)	(i)	What is the average relative atomic mass of titanium? Give your answer to three significant figures.

(2)
 
(ii)	What instrument would have been used to find this percentage composition?
............................................................................................................................
(1)

(b)	(i)	Give the electronic configuration of a titanium atom, using s p d notation.
............................................................................................................................
(2)
(ii)	Name the part of the Periodic Table where titanium appears.
............................................................................................................................
(1)
 
(c)	Titanium occurs naturally as rutile, TiO2. One possible method of obtaining pure titanium is to heat rutile with carbon.
TiO2(s)  +  2C(s)  ®  Ti(s)  +  2CO(g)
(i)	What type of reaction is this?
............................................................................................................................
(1)
 
(ii)	Calculate ΔH for this reaction given that
ΔHfο [TiO2(s)] = –940 kJ mol–1
ΔHfο [CO(g)] = –110 kJ mol–1
	Include a sign and units in your answer.

(3)
 
(iii)	Name the law you have used in your calculation.
............................................................................................................................
(1)

(iv)	When titanium is manufactured by this method, explain what pollution problem arises.
............................................................................................................................
............................................................................................................................
............................................................................................................................
(2)
(Total 13 marks)

13.	(a)	State the meaning of the terms
(i)	relative atomic mass
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
 
(ii)	mass number
..........................................................................................................................
..........................................................................................................................
(1)
 
(iii)	isotopes
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)

(b)	The isotopic composition of a sample of sulphur is found using a mass spectrometer.
(i)	Explain how atoms of the sample of sulphur are ionised.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
 
(ii)	State the type of charge on the sulphur ions formed in the mass spectrometer.
..........................................................................................................................
(1)
 
(iii)	State how the resulting sulphur ions are then accelerated.
..........................................................................................................................
(1)
 
(c)	For a particular sample of sulphur atoms the following isotopic composition was recorded.
Isotope	Percentage composition	
32S	95.00	
33S	0.76	
34S	4.24	

	Calculate the relative atomic mass of this sample of sulphur. Give your answer to two decimal places.

(2)
 
(d)	Predict the electronic configuration of a 34S atom, using s, p and d notation.
1s2 .........................................................................................................................
(1)
(Total 12 marks)

14.	(a)	State and explain the trend in the boiling temperatures of the noble gases. 
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
(3)

(b)	The graph below shows the melting temperatures of the elements of Period 3 of the Periodic Table, sodium to argon, plotted against atomic number.

(i)	Identify one of the elements above that is composed of simple molecules at room temperature.
......................................................................................................................
(1)
 
(ii)	Silicon has a giant atomic structure. Explain how this structure results in the high melting temperature shown on the graph.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(2)

(iii)	Explain why the melting temperature of magnesium is higher than that of sodium.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(3)
(Total 9 marks)

15.	(a)	An atom of gallium has mass number 69.
	Complete the table to show the number of sub-atomic particles in this gallium atom.
Electrons	Neutrons	Protons	
			
(2)
 
(b)	The mass spectrum of a sample of gallium is shown below.

	What is the average relative atomic mass of gallium in this sample? Give your answer to three significant figures.

(2)
 
(c)	What type of bonding would you expect to find in gallium?
......................................................................................................................................
(1)
(Total 5 marks)

16.	(a)	Complete the electronic configurations of the following noble gases.
(i)	Neon: 1s2 ....................................................................................................................
(1)
(ii)	Krypton: 1s2 ................................................................................................................
(1)
 
(b)	Explain whether krypton or neon has the higher boiling temperature.
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
(2)
 
(c)	A mass spectrometer can be used to analyse a sample of a certain element.
	Explain how each of the following is achieved in a mass spectrometer.
(i)	Ionisation: ...................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(ii)	Acceleration: ..............................................................................................................
.....................................................................................................................................
(1)
(iii)	Deflection: ..................................................................................................................
.....................................................................................................................................
(1)
(Total 8 marks)

17.	(a)	Define the term relative atomic mass.
............................................................................................................................................
............................................................................................................................................
............................................................................................................................................
............................................................................................................................................
(2)
 
(b)	Give the symbol, including the atomic number and mass number, of the isotope whose nucleus contains two more protons and three more neutrons than the isotope .
...........................................................................................................................................
(2)
 
(c)	The table below shows the first five successive ionisation energy values for an element.
Ionisation energy	Value/kJ mol–1	
1st	577	
2nd	1820	
3rd	2740	
4th	11600	
5th	14800	
	Use this data, and the Periodic Table, to suggest an element which could have produced these results.  Explain your answer.
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
(2)
(Total 6 marks)

18.	(a)	A 2.20 g sample of potassium nitrate, KNO3, was dissolved in water to produce 50.0 cm3 of potassium nitrate solution.
	Calculate the concentration of this solution in mol dm–3.

(2)
 
(b)	A 2.20 g sample of potassium nitrate was heated strongly and the following reaction occurred.
2KNO3(s) ® 2KNO2(s) + O2(g)
(i)	Calculate the mass of potassium nitrite, KNO2, produced.

(2)

(ii)	Calculate the volume of oxygen gas produced.
	(One mole of gas occupies a volume of 24.0 dm3 under the conditions of the experiment).

 
(2)
(c)	State and explain the trend in the thermal stability of the nitrates of Group I as the atomic number increases.
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
(3)

(d)	An analysis of a potassium compound gave the following results.
Element	Percentage by mass	
potassium	56.5%	
carbon	8.7%	
oxygen	34.8%	
	Deduce the empirical formula of this compound.

(3)
(Total 12 marks)

19.	Explain each of the following.
	Silicon and phosphorus are both covalent substances, but silicon has a much higher melting temperature than phosphorus.
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
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(Total 5 marks)

20.	The element gallium has two isotopes.
	
(a)	(i)	State ONE similarity and ONE difference between these two isotopes in terms of the numbers of their fundamental particles.
Similarity ..........................................................................................................
Difference .........................................................................................................
(2)

(ii)	The molar mass of a sample of gallium is 69.8 g mol–1.
	Calculate the percentage abundance of the isotope in the sample.

(2)
 
(b)	The first four ionisation energies of gallium are plotted below.

(i)	Write the chemical equation, with state symbols, which corresponds to the first ionisation energy of gallium.

(2)

(ii)	Why is there a general rise in the ionisation energy as successive electrons are removed?
..........................................................................................................................
..........................................................................................................................
(1)
 
(iii)	Explain why there is a comparatively large increase in value between the third and fourth ionisation energies.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
 
(c)	(i)	Suggest the formula of gallium chloride.
(You may find it helpful to refer to the Periodic Table.)
..........................................................................................................................
(1)
 
(ii)	Gallium chloride dissolves in water to form a solution containing ions.
	Suggest an experiment to show that the solution contains ions. State the result you would expect.
Experiment .......................................................................................................
..........................................................................................................................
..........................................................................................................................
Result ...............................................................................................................
(2)
(Total 12 marks)

21.	(a)	A sample of an element can be analysed using a mass spectrometer. State how the following are achieved in this instrument:
(i)	ionisation.....................................................................................................................
.....................................................................................................................................
(2)
(ii)	deflection.....................................................................................................................
.....................................................................................................................................
 
(b)	The following data were obtained from the mass spectrum of a sample of gallium.
Peak at m/e	%	
69.0	60.4	
71.0	39.6	
	Calculate the relative atomic mass of this sample of gallium, to 3 significant figures.

(2)

(c)	An atom contains five protons and five neutrons.
(i)	Give the symbol for this atom, including the mass number.
.....................................................................................................................................
(2)
(ii)	Complete the electronic configuration of this atom.
1s2 ...............................................................................................................................
(1)
(iii)	Give the formula of the compound formed between this element and chlorine.
.....................................................................................................................................
(1)
(Total 9 marks)

22.	(a)	(i)	Define the term first ionisation energy.
................................................................................................................................
................................................................................................................................
................................................................................................................................
................................................................................................................................
................................................................................................................................
(3)
 
(ii)	State and explain the general trend in the first ionisation energy across the period sodium to argon of the Periodic Table.
................................................................................................................................
................................................................................................................................
................................................................................................................................
................................................................................................................................
................................................................................................................................
(3)

(b)	(i)	Write an equation to illustrate the process occurring when the second electron affinity of nitrogen is measured.
...............................................................................................................................
(2)
 
(ii)	Explain why the second electron affinity of any element is endothermic.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(Total 10 marks)

23.	An isotope of the element bohrium, , was recently discovered. How many neutrons are there in a nucleus of this isotope?
...............................................................................................................................................
(Total 1 mark)

24.	Write the electron configuration of a magnesium atom, using the s, p, d notation.
................................................................................................................................................
(Total 1 mark)

25.	Sodium is a reactive, silver-grey element from Group 1 of the Periodic Table.
(a)	(i)	What name is given to the type of bonding in this element? Draw a diagram to illustrate this type of bonding.
Name .................................................................................................................

(2)
 
(ii)	Sodium reacts readily with other elements such as chlorine.
		2Na(s)	+	Cl2(g)		2NaCl(s)
	sodium		chlorine		sodium chloride
	Draw a ‘dot-and-cross’ diagram, showing outer electrons only, of the ionic compound sodium chloride. Indicate charges clearly on your diagram.

(2)

(iii)	Would you expect the radius of a sodium ion to be larger than, smaller than or the same as the radius of a sodium atom? Give TWO reasons to justify your answer.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
(3)
 
(b)	The table shows the first four ionisation energies for another element.
Ionisation Energy / kJ mol–1	
1st	2nd	3rd	4th	
738	1451	7733	10 541	
	To which Group of the Periodic Table does the element belong? Use the data to give a reason for your answer.
Group ..........................................................................................................................
Reason .........................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)

(c)	The graph below shows the first ionisation energies of the elements in Period 3. One noticeable feature of this graph is the dip from magnesium to aluminium. Use your knowledge of quantum levels and sub-levels to suggest an explanation for this dip.

....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
.................................................................................................................................
(2)

(d)	The Periodic Table shown here is from a website designed to help students understand the idea of periodicity. The heights of the shaded bars represent the melting points of the elements.

Source: www.schoolscience.co.uk/ptgraphs.html
 
(i)	Another table on this website shows the boiling points of the elements. 
Suggest ONE similarity and ONE difference between the two tables.
Similarity
............................................................................................................................
............................................................................................................................
Difference
............................................................................................................................
............................................................................................................................
(2)
 
(ii)	Name ONE other physical property, not mentioned in this question, that exhibits periodicity.
............................................................................................................................
(1)
(Total 14 marks)

26.	The element bromine has an atomic number of 35 and has two isotopes of relative isotopic mass 79 and 81.
(a)	(i)	Define the term relative isotopic mass.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
 
(ii)	Complete the table below.
Atom	Number of protons	Number of neutrons	
79Br			
81Br			
(3)
 
(b)	Bromine gas has the formula Br2. When a sample of bromine gas was analysed in a mass spectrometer, three peaks were obtained of m/e values of 158, 160 and 162.
	Give the formulae of the species responsible for the peaks with m/e values 158, 160 and 162.
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
(3)
(Total 8 marks)

27.	(a)	Complete the electronic configuration of an
Al atom	ls2.........................................................................................................................
Al3+ ion	ls2.........................................................................................................................
(2)
 
(b)	Describe the structure of aluminium metal and explain why it conducts electricity.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
(3)
 
(c)	(i)	Define the term first ionisation energy.
................................................................................................................................
................................................................................................................................
................................................................................................................................
................................................................................................................................
(3)
 
(ii)	Explain why the first ionisation energy of aluminium is less than that of magnesium.
................................................................................................................................
................................................................................................................................
................................................................................................................................
................................................................................................................................
................................................................................................................................
(2)
(Total 10 marks)

28.	(a)	Complete the electronic configuration for calcium, Ca.
1s2 .................................................................................................................................
(1)

(b)	(i)	Define the term first ionisation energy.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
(3)
 
(ii)	Explain why the first ionisation energy of calcium is lower than that of magnesium.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
(3)
 
(c)	A sample of magnesium contains three isotopes of mass numbers 24, 25 and 26.
(i)	In terms of sub-atomic particles, state ONE similarity and ONE difference between these isotopes.
Similarity ...........................................................................................................
............................................................................................................................
Difference ..........................................................................................................
............................................................................................................................
(2)

(ii)	The following data were obtained from the mass spectrum of this sample of magnesium.
Peak at m/e	%
24.0	78.6
25.0	10.1
26.0	11.3
	Calculate the relative atomic mass of this sample of magnesium. Give your answer to 3 significant figures.

(2)
(Total 11 marks)

29.	(a)	(i)	Write a balanced equation which represents the change that corresponds to the second ionisation energy of magnesium. Include state symbols in your answer.

(2)

(ii)	The graph below shows how the second ionisation energy of six consecutive elements in the Periodic Table, represented by the letters A to F, varies with increasing atomic number.

	Which of the elements, A to F, could represent magnesium?
..........................................
(1)
 
(b)	Draw a ‘dot and cross’ diagram to show the ions in magnesium fluoride.
Include all electrons and the charges on the ions.

(2)
(Total 5 marks)

30.	(a)	One of the naturally occurring potassium isotopes is 39K.
(i)	Write down the numbers of protons, neutrons and electrons present in an atom of 39K. Use the Periodic Table as a source of data.
	protons ......................	electrons ....................
	neutrons ....................
(2)
 
(ii)	Write down the electronic configuration of a potassium atom using s,p,d notation.
...............................................................................................................................
(1)
 
(b)	To show that potassium manganate(VII), KMnO4, is ionic, the apparatus below can
be used.

	The power supply is connected for about 30 minutes.
 
(i)	Give the formula of the coloured ion present in potassium manganate(VII),
KMnO4.
...............................................................................................................................
(1)

(ii)	What would you expect to see after 30 minutes?
................................................................................................................................
................................................................................................................................
................................................................................................................................
................................................................................................................................
(1)
 
(iii)	The gel was replaced with one containing copper(II) sulphate and the experiment repeated. Describe and explain what would be seen.
................................................................................................................................
................................................................................................................................
................................................................................................................................
................................................................................................................................
................................................................................................................................
................................................................................................................................
(2)
(Total 7 marks)
	Diagram adapted from Nuffield Advanced Science Chemistry Student’s Book, 4th Edition, p. 64, Fig. 3.20.

31.	(a)	Sodium chloride, NaCl, can be made by the reaction of sodium with chlorine.
2Na(s) + Cl2(g) ® 2NaCl(s)
(i)	Calculate the maximum mass of sodium chloride which could be obtained from 92 g of sodium.

(2)
 
(ii)	Calculate the concentration of the solution obtained when this mass of sodium chloride is dissolved in water and made up to a volume of 10 dm3 with distilled water.

(1)
 
(iii)	Calculate the volume of chlorine gas required to react with 92 g of sodium.
	[1 mol of gas occupies 24 dm3 under the conditions of the experiment]

(2)

(b)	Describe the structure of solid sodium metal and explain why it conducts electricity.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
 
(c)	(i)	Define the term first ionisation energy.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(3)
 
(ii)	Explain why the first ionisation energy of chlorine is higher than that of sodium.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(Total 13 marks)

32.	(a)	An atom of argon has mass number 40. Complete the table below showing the composition of this argon atom.
	Use the Periodic Table as a source of data.
Protons		
Electrons		
Neutrons		
(2)
 
(b)	An atom of potassium has mass number 39. Explain, in terms of atomic structure, why argon comes before potassium in the Periodic Table.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(1)
 
(c)	A sample of argon contains a mixture of isotopes as shown below.
	Calculate the relative atomic mass of argon in the sample. Give your answer to three significant figures.
Isotopic mass	% abundance	
36.0	1.34	
38.0	0.160	
40.0	98.5	

(2)

(d)	Write the electron configuration of argon in s, p notation.
.....................................................................................................................................
(1)
 
(e)	The chart shows the first ionisation energy of some elements in the third period of the Periodic Table.

(i)	Write the chemical equation, with state symbols, which corresponds to the first ionisation energy of argon.
...........................................................................................................................
(1)
 
(ii)	On the chart, add a cross to show the first ionisation energy of potassium. Justify your choice of the position of the cross.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)

(iii)	Explain why there is a small decrease in first ionisation energy going from phosphorus to sulphur.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
 
(iv)	Explain why there is an increase in first ionisation energy going from sulphur to chlorine.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
 
(f)	Suggest why argon is used to fill some types of light bulbs.
.....................................................................................................................................
.....................................................................................................................................
(1)
(Total 14 marks)

33.	(a)	Complete the electron configuration for carbon.
1s2 ........................................................................
(1)

(b)	Explain how successive ionisation energy data could be used to confirm that carbon is in Group 4 of the Periodic Table.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(1)
 
(c)	Draw a dot and cross diagram for a molecule of carbon tetrachloride, CCl4, showing outer electrons only.

(2)
 
(d)	Explain how the following are achieved in a mass spectrometer.
(i)	Ionisation
...........................................................................................................................
...........................................................................................................................
 
(2)
(ii)	Deflection
...........................................................................................................................
(1)

(e)	(i)	Define the term relative isotopic mass.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(3)
 
(ii)	Carbon consists of the isotopes 12C, 13C and 14C. Chlorine consists of the isotopes 35Cl and 37Cl.
	Use this data to calculate the maximum relative molecular mass of a molecule of carbon tetrachloride, CCl4.

(1)
 
(iii)	Explain, in terms of sub-atomic particles, the meaning of the term isotopes.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)

(iv)	Why do isotopes of the same element have the same chemical properties?
...........................................................................................................................
...........................................................................................................................
(1)
(Total 14 marks)

34.	(a)	Sodium iodide reacts with chlorine to produce sodium chloride and iodine.
(i)	State the oxidation numbers of the iodine and chlorine species in the spaces provided.
	2NaI	+	Cl2	→	2NaCl	+	I2
	..........		..........		..........		.........
(2)
 
(ii)	Use these oxidation numbers to explain why this reaction is a redox reaction.
...........................................................................................................................
...........................................................................................................................
(2)

(iii)	Calculate the maximum mass of iodine that could be produced from 30.0 g of sodium iodide.

(3)
 
(iv)	Calculate the volume of chlorine gas required to produce this amount of iodine.
	[1 mol of gas occupies 24 dm3 under the conditions of the experiment]

(1)
 
(b)	(i)	Give the colour of iodine and its physical state at room temperature and pressure.
Colour ........................................................................................
Physical state .............................................................................
(2)

(ii)	Write an equation, including state symbols, to represent the process occurring when the first ionisation energy of iodine atoms is measured.
...........................................................................................................................
(2)
(Total 12 marks)

35.	(a)	Complete the table below which is about isotopes and an ion of magnesium.
	Numbers of	
	Protons	Neutrons	Electrons	
	12	12		
	12		12	
	12	12		
(3)
 
(b)	Complete the electronic configurations of magnesium and chlorine atoms.
		1s	2s	2p	3s	3p
Mg	↓↑		↓↑											
(1)
		1s	2s	2p	3s	3p
Cl	↓↑		↓↑											
(1)
 
(c)	Write the equation, including state symbols, for the reaction of magnesium with chlorine.
.....................................................................................................................................
(2)

(d)	The mass spectrum of a sample of chlorine molecules shows three molecular peaks.
These are formed from the molecules shown below.
Molecule	Percentage abundance	
35Cl-35Cl	56.25	
35Cl-37Cl	37.50	
37Cl-37Cl	6.25	
	Calculate the relative molecular mass of chlorine in this sample.

(2)
 
(e)	Calculate the volume of 4.73 g of chlorine gas at 100 °C.
	[The molar volume of a gas at 100 °C = 30.6 dm3 mol–1]

(2)
 
(f)	State and explain the type of bond that exists in solid magnesium.
Type ..............................................................
Explanation  ................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
 
(g)	State the type of bond that exists in magnesium chloride. Draw a dot and cross diagram showing the outer shell electrons.
Type ..............................................................
Dot and cross diagram

(3)
(Total 17 marks)

36.	(a)	Define the term
(i)	atomic number
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(1)
(ii)	mass number
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(1)

(b)	First ionisation energies of the elements show periodicity. The graph below shows the first ionisation energy of twelve successive elements in the Periodic Table in order of increasing atomic number.
The letters are not the symbols for the elements.

(i)	Give the letters of the two elements in Group 0 (the noble gases).
	Explain your answer in terms of ionisation energy.
Letters .................... and ....................
Explanation .......................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)

(ii)	Give the letter of the Group 3 element.
	Explain your answer in terms of ionisation energy.
Letter ....................
Explanation .......................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
 
(iii)	Explain why there is an increase in the first ionisation energy of the elements from F to H shown on the graph on the previous page.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(Total 8 marks)

37.	A sample of gallium, Ga, (atomic number 31) was found to consist of two different types of atoms with mass numbers 69 and 71. 60.2% of the sample had the lower mass number.
(a)	What is the name given to atoms of the same element with different mass numbers?
.....................................................................................................................................
(1)
 
(b)	How many neutrons are there in an atom of gallium with mass number 71?
..............................................
(1)
 
(c)	(i)	What instrument would be used to obtain the percentage composition of the gallium sample?
...........................................................................................................................
(1)
 
(ii)	Calculate the average atomic mass of gallium in this sample. Show your working and give your answer to 3 significant figures.

(2)
 
(d)	(i)	Complete the electron configuration of a gallium atom, using the s p d notation.
1s2 ......................................................................................................................
(2)
 
(ii)	Write a balanced equation which represents the change that corresponds to the first ionisation energy of gallium. Include state symbols in your answer.

(2)

(iii)	The first four ionisation energies, in kJ mol–1, of the Group 3 elements gallium and indium and the Group 4 elements germanium and tin are shown below.
	A	558	1821	2705	5200
B	579	1979	2963	6200
C	709	1412	2943	3930
D	762	1537	3302	4411
Which set of figures, A, B, C or D, represents gallium? ..................................
(1)
(Total 10 marks)

38.	(a)	Complete the table below which is about the isotopes and an ion of bromine.
	Number of	
	protons	neutrons	electrons	
	35		35	
		46	35	
	35	46		
(3)
 
(b)	Complete the electronic configurations of
Na 1s2 ..........................................................................................................................
Br 1s2 ...........................................................................................................................
(2)
 
(c)	Explain why the isotopes of bromine have identical chemical reactions.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(1)

(d)	What instrument could be used to measure the abundance and mass of the isotopes of bromine?
.....................................................................................................................................
(1)
 
(e)	The isotopic abundance of bromine is shown below.
Relative isotopic mass	Percentage abundance	
78.93	50.54	
80.91	49.46	
	Calculate the relative atomic mass of bromine. Give your answer to four significant figures.

(2)
 
(f)	State the types of bonding present in bromine liquid
between the atoms .......................................................................................................
between the molecules ................................................................................................
(2)
(Total 11 marks)

39.	(a)	(i)	Define the term first ionisation energy.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(3)
 
(ii)	Write the equation for the process occurring when the second ionisation energy of oxygen is measured.
...........................................................................................................................
(1)
 
(b)	The graph below shows the first seven successive ionisation energies of an element, X, which is in Period 3 of the Periodic Table.

(i)	Use the information on the graph to state in which Group of the Periodic Table X is found. Justify your answer.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
 
(ii)	Identify the element X.
...........................................................................................................................
(1)
 
(c)	The mass spectrum of X shows a singly charged molecular ion at m/e = 256.
	Write the formula of this ion.
.....................................................................................................................................
(2)
(Total 9 marks)

40.	Some of the ionisation energies of four elements, Q, R, S and T, with consecutive atomic numbers, are shown in the table below.
Ionisation Energies / kJ mol–1	
1st	2nd	3rd	4th	5th	
Q	2081	3952	6122	9370	12177	
R	496	4563	6913	9544	13352	
S	738	1451		10541	13629	
T		

(a)	To which group of the Periodic Table does R belong? Give a reason for your answer.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
 
(b)	Estimate values, in kJ mol–1, for the third ionisation energy of S, and the first ionisation energy of T, represented by the shaded gaps shown in the table above.
S ..........................
T ..........................
(2)
 
(c)	Which element is least likely to form compounds? Give a reason for your answer.
.....................................................................................................................................
.....................................................................................................................................
(1)
 
(d)	Write a balanced equation which represents the change that corresponds to the third ionisation energy of R.
	Use R as the symbol for the element and include state symbols in your answer.

(2)

(e)	Element X is in the same group of the Periodic Table as R, but is immediately below it. The first ionisation energy of X is 419 kJ mol–1. Explain why this value is lower for X than for R.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(1)
(Total 8 marks)

41.	(a)	Complete the electronic configuration of a copper atom and a bromide ion.
(i)	Copper atom, Cu	1s22s22p63s23p6 ..............................................................
(1)
(ii)	Bromide ion, Br–	1s22s22p63s23p6 ..............................................................
(1)
 
(b)	Define the term relative atomic mass.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)

(c)	The following data were obtained for a mass spectrum of a sample of copper.
Relative isotopic mass	Percentage abundance	
62.93	69.17	
64.93	30.83	
	Calculate the relative atomic mass of this sample of copper. Give your answer to two decimal places.

(2)
 
(d)	Copper occurs naturally as the mineral malachite. The composition, by mass, of malachite is as follows:
	Cu = 57.5% C = 5.4% O = 36.2% H = 0.9%
(i)	Calculate its empirical formula.

(2)

(ii)	The molar mass of malachite is 221 g mol–1. Calculate its formula.

(1)
 
(e)	Copper forms a chloride, CuCl2. Use the data below to calculate the maximum and the minimum values for the molar mass of CuCl2.
Data :	Relative isotopic masses of chlorine are 35 and 37.
Relative isotopic masses of copper are 63 and 65.

(2)
(Total 11 marks)

42.	First ionisation energy and melting temperature are periodic properties shown by elements.
(a)	Define the term first ionisation energy.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)

(b)	Explain why the first ionisation energy of potassium is less than that of sodium.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
 
(c)	The table shows the melting temperatures of the elements of period 3.
	Na	Mg	Al	Si	P
(white)	S	Cl	Ar	
Melting temperature
/K 	371	923	933	1683	317	392	172	84	
Type of structure 				
 
(i)	Complete the table to suggest the type of structure shown by the elements.
Choose your answers from the following list:
giant atomic structure: metallic structure: simple molecular.
(1)
 
(ii)	Explain why silicon has a very high melting temperature.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)

(iii)	Explain why aluminium has a higher melting temperature than sodium.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(Total 11 marks)

43.	The diagram below shows the arrangement of electrons in the energy levels of a sodium atom.

(i)	Why are the two electrons shown in the n = 1 energy level represented by arrows pointing in opposite directions?
.....................................................................................................................................
.....................................................................................................................................
(1)
 
(ii)	Draw an arrow on the diagram to represent the energy change when a sodium atom ionises by losing an electron.
(2)
 
(iii)	Do all of the electrons in the n = 2 energy level have the same energy? Explain your answer.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
 
(iv)	How would the arrangement of electrons in a potassium atom differ from this arrangement of electrons in sodium?
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(1)
(Total 6 marks)

44.	(a)	A sample of an element can be analysed to show its isotopic composition using a mass spectrometer.
(i)	Explain how the sample is ionised.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
 
(ii)	State the TWO properties of the ion that determine the path of the ion through the magnetic field.
...........................................................................................................................
...........................................................................................................................
(2)

(b)	Define relative isotopic mass.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
 
(c)	The following data were obtained from the mass spectrum of a sample of chromium.
Relative isotopic mass	Percentage abundance	
49.95	4.345	
51.94	83.79	
52.94	9.501	
53.94	2.364	
	Calculate the relative atomic mass of this sample of chromium.
	Give your answer to four significant figures.

(2)
 
(d)	Complete the electron configuration of an iron atom, atomic number 26.
1s	2s	2p	3s	3p	3d	4s	
↑↓	↑↓	↑↓	↑↓	↑↓											
(2)
(Total 10 marks)

45.	(a)	The graph below shows the first ionisation energies of the elements Li, Be, and B.
	Complete the graph by adding the approximate first ionisation energies of the elements C to Ne.

(2)

(b)	Explain why the general trend is for the first ionisation energy to increase across the period.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
 
(c)	Explain why the first ionisation energy of boron, B, is lower than that of beryllium, Be.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(Total 7 marks)

46.	A sample of the element osmium, atomic number 76, is made up of four isotopes. The sample has the following percentage composition.
Relative Atomic
Mass of Isotope	% Composition	
188	15.20	
189	17.40	
190	26.40	
192	41.00	
 
(i)	What is the minimum number of neutrons present in any single atom of osmium in the sample?
.....................................................................................................................................
(1)
 
(ii)	Calculate the average relative atomic mass of osmium in the sample. Give your answer to four significant figures.

(2)
(Total 3 marks)

47.	Going across a period in the Periodic Table from left to right, the general trend is that
A	the bonding in the element itself changes from ionic to covalent
B	the number of neutrons in the nucleus increases
C	the first ionisation energy decreases
D	the metallic character increases
(Total 1 mark)

48.	The electron configurations of argon, iron, chlorine and one other element are given below, but not in order. Which one represents the unnamed element?
A	1s2 2s2 2p6 3s2 3p6 3d6 4s2
B	1s2 2s2 2p6 3s2 3p6
C	1s2 2s2 2p6 3s2 3p4
D	1s2 2s2 2p6 3s2 3p5
(Total 1 mark)

49.	Buckminsterfullerene is a carbon molecule with formula C60 which can trap metal ions in its structure. Which of the following compounds of buckminsterfullerene would give a line of mass/charge ratio at 837.3 in a mass spectrometer?
A	Na4C60
B	K3C60
C	Ca3C60
D	AgC60
(Total 1 mark)

50.	Which of the following equations represents the first ionisation of sulfur?
A	S(s) + e– ® S–(g)
B	S(g) + e– ® S–(g)
C	S(s) ® S+(g) + e–
D	S(g) ® S+(g) + e–

(Total 1 mark)

51.	Which element marked on this graph is a halogen?

A
B
C
D
(Total 1 mark)

52.	This question is about the following ionisation energy sequences.
	The values are all in kJ mol–1.
A	1400	1000	950	830	700
B	420	3100	4400	5900	8000
C	1000	1250	1520	420	590
D	1520	2700	3900	5800	7200

	Select from A to D the sequence which is most likely to represent the following:
(a)	The first ionisation energies of five consecutive members of the same group in the Periodic Table, in order of increasing atomic number.
A
B
C
D
(1)
 
(b)	The first five ionisation energies of an s-block element.
A
B
C
D
(1)
 
(c)	The first five ionisation energies of a noble gas.
A
B
C
D
(1)
(Total 3 marks)

53.	This question is about four hydrocarbons with molecular formulae as shown.
A	C2H2
B	C3H6
C	C3H8
D	C4H10
 
(a)	Which hydrocarbon has the same empirical formula as its molecular formula?
A
B
C
D
(1)
 
(b)	Which has a molecular ion in the mass spectrum at mass/charge ratio = 58?
A
B
C
D
(1)
 
(c)	Which is neither an alkane nor an alkene?
A
B
C
D
(1)
 
(d)	Which could be 2-methylpropane?
A
B
C
D
(1)
(Total 4 marks)

54.	Copper(II) sulfate solution can be prepared from solid copper(II) carbonate by reaction with hot dilute sulfuric acid.
(a)	Write the equation for the reaction, including state symbols.

(1)
 
(b)	The experiment was carried out using 0.025 moles of sulfuric acid of concentration 2.0 mol dm–3. What volume of this sulfuric acid was used?

(1)
 
(c)	(i)	It is usual to react the sulfuric acid with a slight excess of copper(II) carbonate.
	Calculate the mass of copper(II) carbonate needed if a 10% excess is required.
	[Molar mass of copper(II) carbonate = 123.5 g mol–1]

(2)

(ii)	A student doing this experiment chose to use a balance reading to 0.01g in an attempt to work accurately.
	Was this choice of balance necessary from the point of view of accuracy? Explain your answer.
...........................................................................................................................
...........................................................................................................................
(1)
 
(d)	The sulfuric acid is heated to boiling and the copper(II) carbonate is added in small portions.
	State the next step needed to prepare pure copper(II) sulfate solution. Justify your answer.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(1)
 
(e)	When the solution of copper(II) sulfate is allowed to crystallise, the crystals which are produced have the formula CuSO4.5H2O.
(i)	What is the molar mass of CuSO4.5H2O?

(1)

(ii)	3.98 g of CuSO4.5H2O crystals were obtained. Calculate the percentage yield in this experiment.

(2)
(Total 9 marks)

55.	This question is about magnesium and magnesium oxide.
(a)	Describe the bonding in magnesium and explain why it is a good conductor of electricity.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
 
(b)	Draw a diagram (using dots or crosses) for the ions in magnesium fluoride showing all the electrons and the ionic charges on:
(i)	the magnesium ion

(1)
(ii)	the fluoride ion.

(1)

(c)	Under what conditions does magnesium fluoride conduct electricity?
	Explain your answer.
.....................................................................................................................................
.....................................................................................................................................
(1)
 
(d)	The mass spectrum of a sample of magnesium is shown below.

(i)	Use the data above to estimate the percentage isotopic composition of the sample of magnesium. Hence calculate the average atomic mass of the sample of magnesium.

(2)
 
(ii)	Why do the three isotopes have the same chemical properties?
...........................................................................................................................
...........................................................................................................................
(1)
 
(e)	(i)	Oceanographers studying plankton found that a sample of seawater contained 1.20 nanomol dm–3 of chlorophyll, C55H77MgN4O5. (1 nanomol = 1 × 10–9 mol)
	What mass of magnesium would be present in 1.00 cm3 of this sample of seawater? Give your answer to three significant figures.

(2)
(ii)	X-ray diffraction can be used to locate atoms or ions in molecules like chlorophyll.
X-rays are scattered by the electrons in atoms and ions. In chlorophyll the atoms of one of the elements still cannot be located with certainty by this technique.
	Suggest which element is most difficult to locate.
...........................................................................................................................
...........................................................................................................................
(1)
(Total 12 marks)