Unit 1 – Electron Structure
Unit 1 - Jan 2009
Q1.
(a)  Define the term first ionization energy.
(3)
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(b)  Write an equation, with state symbols, to illustrate the process occurring when the second ionization energy of sodium is measured.
(2)

(c)  The graph below shows the variation in the first ionization energies of some of the
       elements in Period 3.

(i)   On the graph, use crosses to show the approximate values of the first ionization energies for the elements Na, P and S. Join the crosses to complete your graph.
(3)
*(ii)   Explain why the first ionization energies generally increase across the period sodium to argon (Na to Ar).
(3)
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*(iii)   Explain why the first ionization energy of aluminium is less than that of magnesium.
(2)
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(d)  Place the following species

in order of increasing first ionization energy, starting with the lowest.
(1)

(Total for question = 14 marks)

Q2.
(a)  (i)   Complete the electronic configuration of the magnesium atom.
(1)
1s2
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(ii)   Complete the electronic configuration of the chlorine atom.
(1)
1s2
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(b)  (i)   Write the equation, including state symbols, for the reaction of magnesium with chlorine.
(2)

(ii)  Name the type of bonding present in magnesium chloride.
(1)
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(iii)   Draw a diagram (using dots or crosses) to show the bonding in magnesium chloride.  Include ALL the electrons in each species and the charges present.
(3)

(c)  State the type of bonding that exists in solid magnesium.
(1)
Type
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*(d)  Explain fully why the melting temperature of magnesium is higher than that of sodium.
(3)
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(Total for question = 12 marks)
Q3.
(a)  A gaseous sample of an element can be analysed using a mass spectrometer.
(i)   Describe briefly how positive ions are formed from gaseous atoms in a mass spectrometer.
(2)
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(ii)   What is used to accelerate the positive ions in a mass spectrometer?
(1)
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(iii)   What is used to deflect the positive ions in a mass spectrometer?
(1)
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(b)  The following data were obtained from the mass spectrum of a sample of chromium.

Calculate the relative atomic mass of chromium in this sample.  Give your answer tothree significant figures.
(2)

(c)  Explain why the four isotopes of chromium behave identically in chemical reactions.
(1)
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 (d)  In which block of the Periodic Table is chromium found?
(1)
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(Total for question = 8 marks)
Q4.
 The first five ionization energies of an element, Z, are:
 790, 1600, 3200, 4400, 16100 kJ mol−1

 In which group of the Periodic Table is Z found?
   A     2
   B     3
   C     4
   D     5
(Total for question = 1 mark)

Unit 1 - Jun 2009
Q5.
The Born-Haber cycle for the formation of sodium chloride from sodium and chlorine
 may be represented by a series of steps labelled A to F as shown.

(a)  (i)  Complete the table below by adding the letters A to F next to the corresponding
             energy changes.
(3)

(ii)  Calculate the first electron affinity of chlorine, in kJ mol−1, from the data given.
(2)

(b)  Lattice energies can be calculated from electrostatic theory (theoretical values) as well as by Born-Haber cycles (experimental values).

(i)  Comment on the fact that there is close agreement between the values for sodium chloride, NaCl.
(1)
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*(ii)  Explain, in terms of chemical bonding, why the experimental value for silver iodide, AgI, is more exothermic than the value calculated theoretically for the same compound.
(2)
*(c)  Suggest why the first ionization energies of the Group 1 elements decrease down the
         group.
(2)
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(Total for question = 10 marks)

Q6.
Which of the following formulae for compounds of germanium, Ge, is unlikely to be correct, given the position of germanium in the Periodic Table?
   A     GeF3
   B     GeS2
   C     GeO2
   D     GeH4
(Total for question = 1 mark)
Q7.
The electronic structure of an atom of an element in Group 6 of the Periodic Table could be
   A     1s2 2s2 2p2
   B     1s2 2s2 2p4
   C     1s2 2s2 2p6 3s2 3p6 3d6 4s2
   D     1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6
(Total for question = 1 mark)
Q8.
The electronic configurations of the atoms of four different elements are given below. For which element would you expect the value of the first ionization energy to be the largest?
   A     1s1
   B     1s2
   C     1s2 2s1
   D     1s2 2s2
(Total for question = 1 mark)

Q9.
The graph shows the variation in melting temperatures of the elements across Period 3 (Na to Ar) of the Periodic Table.

(a)  Complete the table below to show the type of structure and bonding for the elements shown.
(3)

(b)  Explain why silicon has a much higher melting temperature than sulfur.
(2)
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*(c)  Explain why the melting temperature increases from sodium to aluminium.
(2)
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 (d)  Magnesium forms the basic oxide magnesium oxide, MgO.  This oxide is almost insoluble in water.  On gentle warming with dilute sulfuric acid, magnesium oxide reacts to form aqueous magnesium sulfate solution.
*(i)  Describe how you would use the above reaction to prepare a pure sample of magnesium sulfate.
(5)
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(ii)  Suggest what action should be taken if a pupil spilt a small quantity of dilute sulfuric acid on a laboratory bench.
(1)
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(e)  The data in the table below will be useful when answering this question.

Magnesium carbonate reacts with dilute sulfuric acid.

(i)  Explain why the reaction between strontium carbonate and dilute sulfuric acid stops after a few seconds.
(1)
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(ii)  Strontium sulfate is produced when aqueous sodium sulfate is added to aqueous strontium chloride.Give the ionic equation for the reaction, including state symbols.
(2)

(Total for question = 16 marks)

Q10.
Which pair of atomic numbers represents elements which are both in the p-block of the Periodic Table?
   A     4, 8
   B     6, 12
   C     8, 16
   D     10, 20
(Total for question = 1 mark)

Q11.
 The first five successive ionization energies of an element, X, are shown in the table
 below.

Which ion is X most likely to form when it reacts with chlorine?
   A     X+
   B     X2+
   C     X3+
   D     X4+
(Total for question = 1 mark)

Unit 1 - Jan 2010
Q12.
The first ionization energies, in kJ mol-1, of four elements with consecutive atomic numbers are shown below.
A    1680
B    2080
C    496
D    738
(a) Which element could be an inert gas?
(1)
   A      
   B      
   C      
   D      

(b) Which element could be X in a covalent compound with formula HX?
(1)
   A      
   B      
   C      
   D      

(c) Which element could be Y in an ionic compound with formula YH2?
(1)
   A      
   B      
   C      
   D      
(Total for question = 3 marks)

Q13.
The graph below shows the second ionization energy of a series of elements with consecutive atomic numbers.

Which element could be lithium?
   A      
   B      
   C      
   D      
(Total for question = 1 mark)

Q14.
The first five ionization energies, in kJ mol-1, of aluminium are
578     1817     2745     11 578     14 831
The orbitals from which the first five electrons are removed during ionization, starting with the first electron, are
   A      1s  2s  2p  3s  3p
   B      1s  1s  2s  2s  2p
   C      3p  3s  2p  2s  1s
   D      3p  3s  3s  2p  2p
(Total for question = 1 mark)

Q15.
(Total for question = 1 mark)

Q16.
 Going across the Periodic Table from sodium to aluminium,
   A      the melting temperature increases.
   B      the radius of the atom increases.
   C      the radius of the metal ion increases.
   D      the bonding in the element changes from metallic to covalent.
(Total for question = 1 mark)

Unit 1 - Jun 2010
Q17.
 This question is about the properties of ions and ionic compounds.
(a) Solid calcium carbonate, CaCO3, has a giant ionic structure.
(i) Draw a diagram (using dots or crosses) for a calcium ion. Show ALL the electrons and the charge on the ion.
(2)

(ii) Complete the electronic configuration for a calcium ion.
(1)
1s2
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(iii) Would you expect a calcium ion to be bigger, smaller or the same size as a
       calcium atom? Give TWO reasons to explain your answer.
(2)
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 (iv) Explain why ionic compounds have relatively high melting temperatures.
(2)
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 (b) Changes in the concentration of ions in a solution can be estimated by measuring the electrical conductivity of the solution.
(i) Explain why solutions of ions are able to conduct electricity.
(1)
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(ii) Suggest why aqueous solutions of calcium chloride, CaCl2(aq), and barium chloride, BaCl2(aq), of the same molar concentration, have different electrical conductivities.
(1)
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(iii) 1 kg of a solution contains 0.100 mol of calcium ions, Ca2+.What is the concentration of the calcium ions by mass in parts per million (ppm)? [Assume the relative atomic mass of calcium is 40.]
(2)

.....................................ppm
*(c) Some buildings are made from limestone, which is mainly calcium carbonate. Gases in the atmosphere such as sulfur dioxide, SO2, and nitrogen dioxide, NO2, can be responsible for damaging these buildings. Describe how these gases come to be present in the atmosphere and explain how they can damage a limestone building.
(3)
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(d) The lattice energy of calcium chloride, CaCl2, is -2258 kJ mol-1 based on an experimental Born-Haber cycle and -2223 kJ mol-1 based on theoretical calculations. Would you expect its bonding to match the ionic model? Justify your answer.
(1)
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(Total for question = 15 marks)
Q18.
Which of these statements is incorrect?
   A   The atomic radius of metals increases down a Group.	
   B   The trend in the melting temperature of successive elements across Period 2 is similar to that in Period 3.
   C   A metallic structure is held together by attractions between metal atoms and delocalized electrons.
   D   Na+ and O2- ions are isoelectronic.
(Total for question = 1 mark)
Q19.
The sketch graph below shows the trend in first ionization energies for some elements in Periods two and three.

Select, from the elements A to D, the one that
 (a) has atoms with five p electrons.
(1)
   A
   B
   C
   D
(b) is a member of Group 3.
(1)
   A
   B
   C
   D
(c) is likely to be very unreactive.
(1)
   A
   B
   C
   D
(d) normally forms four covalent bonds per atom.
(1)
   A
   B
   C
   D
(Total for question = 4 marks)
Q20.
Which of these equations represents the electron affinity of chlorine?
   A   Mg+(g)         → Mg2+(g) + e-
   B   Mg(g)           → Mg2+(g) + 2e-
   C   Mg+(g) + e-  → Mg2+(g)
   D   Mg(g) + 2e- → Mg2+(g)
(Total for question = 1 mark)

Unit 1 - Jan 2011
Q21.
 This question is about the element chlorine (atomic number = 17).
(a) Complete the electronic structure of chlorine.
(1)
1s2 2s2
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(b) Chlorine forms compounds with magnesium and with carbon.
(i) Draw a dot and cross diagram to show the electronic structure of the compound magnesium chloride (only the outer electrons need be shown). Include the charges present.
(2)

(ii) Draw a dot and cross diagram to show the electronic structure of the compound tetrachloromethane (only the outer electrons need be shown).
(2)

*(iii) Suggest why the melting temperature of magnesium oxide is higher than that of magnesium chloride, even though both are almost 100% ionic.
(3)
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(c) Magnesium chloride may be prepared from magnesium by reaction with chlorine or with hydrochloric acid. Compare these two preparations in terms of the atom economies of the reactions. No calculation is required.
(2)
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(Total for question = 10 marks)

Q22.
The graph below represents the successive ionization energies of an element X plotted against the number of the electron removed. X is not the symbol for the element.

(a) From this graph it is possible to deduce the group in the Periodic Table to which X belongs. X is in
(1)
   A      Group 1 
   B      Group 3 
   C      Group 5 
   D      Group 7 
(b) From the graph it is possible to deduce that the most stable ion of X will be
(1)
   A      X3+
   B      X+
   C      X−
   D      X3−
(Total for question = 2 marks)
Unit 1 - Jun 2011
Q23.
 All alkenes have
   A    the same empirical formula and the same general formula.
   B    the same molecular formula and the same general formula.
   C    the same molecular formula and the same empirical formula.
   D    the same empirical formula and the same structural formula.
(Total for Question = 1 mark)
Q24.
The first ionization energy of each of the elements from neon to argon is shown on the graph below. The first ionization energy of potassium has been omitted.

(a) Define the term first ionization energy.
(3)
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(b) Explain why, in moving from Na to Ar, the general trend is for the first ionization energy to increase.
(3)
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(c) Explain why the first ionization energy decreases from P to S.
(2)
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 (d) Estimate the value of the first ionization energy of potassium, K, and write your answer below.
(1)
................................................ kJ mol−1
(Total for Question = 9 marks)
Q25.
The equation for the complete combustion of pentane is

The standard enthalpy change of formation of CO2(g) is −394 kJ mol−1 and that of H2O(l) is −286 kJ mol−1.
The standard enthalpy change of formation of pentane (in kJ mol−1) is
   A    5(−394) + 6(−286) + (−3509)
   B    5(−394) + 6(−286) − (−3509)
   C    −5(−394) − 6(−286) + (−3509)
   D    −5(−394) − 6(−286) − (−3509)
(Total for Question = 1 mark)

Unit 1 - Jan 2012
Q26.
* The melting temperatures of the elements of Period 3 are given in the table below. Use these values to answer the questions that follow.

(a) Explain why the melting temperature of sodium is very much less than that of magnesium.
(3)
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(b) Explain why the melting temperature of silicon is very much greater than that of white phosphorus.
(3)
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(c) Explain why the melting temperature of argon is the lowest of all the elements of Period 3.
(1)
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(d) Explain why magnesium is a good conductor of electricity whereas sulfur is a non-conductor.
(2)
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 (Total for question = 9 marks)
Q27.
The first eight ionization energies of an element are (in kJ mol−1):
789, 1577, 3232, 4356, 16091, 19785, 23787, 29253.
   A      Group 1
   B      Group 2
   C      Group 3
   D      Group 4
(Total for question = 1 mark)

Unit 1 - Jun 2012
Q28.
 The electronic structures of four elements are given below. Which of these elements has the highest first ionization energy?

(Total for question = 1 mark)

Q29.
(a) Define the term first ionization energy.
(2)
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*(b) Explain why the first ionization energy of the elements down Group 1 decreases even though the atomic number increases.
(2)
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 (c) The eleven successive ionization energies for sodium are given below.

     (i) Explain why the successive ionization energies increase.
(1)
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   *(ii) Explain how these ionization energies give evidence for the electronic structure of sodium. You may use a sketch graph if you wish.
(2)
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(d) The first ionization energy of aluminium (element 13) is lower than that of magnesium (element 12).
     (i) Give the electronic structures of magnesium and of aluminium in s, p and d notation.
(1)
Magnesium
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Aluminium
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   *(ii) Explain the difference in the first ionization energies of the two metals.
(1)
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(Total for question = 9 marks)
Q30.
 If X represents the element of atomic number 9 and Y the element of atomic number 20, the compound formed between these two elements is
   A    covalent, YX2.
   B    ionic, YX2.
   C    covalent, YX.
   D    ionic, YX.
(Total for question = 1 mark)
Q31.
The equation representing the reaction between copper(II) oxide and dilute sulfuric acid is
CuO(s) + H2SO4(aq) → CuSO4(aq) + H2O(l)
The ionic equation for the reaction is
   A    Cu2+(s) + SO42−(aq) → CuSO4(aq)
   B    O2−(s) + H2SO4(aq) → H2O(l) + SO42−(aq)
   C    CuO(s) + 2H+(aq) → Cu2+(aq) + H2O(l)
   D    CuO(s) + H2SO4(aq) → Cu2+SO42−(aq) + H2O(l)
(Total for question = 1 mark)

Q32.
In which of the following cases would a cation be most polarizing?
Radius          Charge
   A                        small               small
   B                        small               large
   C                        large               small
   D                        large               large
(Total for question = 1 mark)

Unit 1 - Jan 2013
Q33.
When an Al4+ ion is formed from an Al atom, the fourth electron is lost from the
   A     1s sub-shell.
   B     2s sub-shell.
   C     2p sub-shell.
   D     3s sub-shell.
(Total for question = 1 mark)

Q34.
Hydrogen has three isotopes, 1H, known as protium, 2H, deuterium, and 3H, tritium.
(a)  In terms of sub-atomic particles, give the similarities and differences between atoms of these three isotopes of hydrogen.
(3)
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(b)  When a nitrogen atom collides with a high energy neutron, one atom of tritium and one atom of another element are formed.  Complete the equation below.
(1)

(c)  Tritium-deuterium gas, consisting of molecules each containing one deuterium atom and one tritium atom, is used in some nuclear warheads.  Typically, each warhead has about 4.0 g of the gas added.
(i)   Calculate the number of moles of tritium-deuterium in 4.0 g.
(2)

(ii)   Calculate the volume, in cm3, of 4.0 g of tritium-deuterium gas.
        [Molar volume of a gas under these conditions = 24 000 cm3 mol−1]
(1)

(d)  Tritium is not usually included in calculations of the relative atomic mass of hydrogen, because it is radioactive and has a relatively short half-life.
        Calculate the relative atomic mass of hydrogen with the following isotopic composition.  Give your answer to four decimal places.
(2)

(e)  The electronic energy levels in hydrogen are shown below.

(i)   Mark on the energy level diagram, with an arrow, the transition that represents the ionization energy of hydrogen.
(1)
(ii)   In some versions of the Periodic Table, hydrogen is placed in the same group as sodium.  Give the electronic configurations for both a hydrogen atom and a sodium atom, using the s and p notation. Use these electronic configurations to suggest why this is a reasonable grouping.
(2)
H
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Na
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*(f)  Which element in the Periodic Table has the highest first ionization energy?  Justify your answer.
(3)
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 (Total for question = 15 marks)
Q35.
White phosphorus consists of
   A     a giant structure of atoms.
   B     a giant structure of ions.
   C     small molecules.
   D     single atoms.
(Total for question = 1 mark)

Unit 1 - Jun 2013
Q36.
Which pair of ions is isoelectronic?
   A    Ca2+ and O2−
   B    Na+ and O2−
   C    Li+ and Cl−
   D    Mg2+ and Cl−
(Total for Question = 1 mark)

Q37.
The first five ionization energies of an element, X, are
578, 1817, 2745, 11578 and 14831 kJ mol−1, respectively.
In which group of the Periodic Table is X found?
   A    1
   B    2
   C    3
   D    4
(Total for Question = 1 mark)

Q38.
Which of the following equations represents the second ionization energy of chlorine?
   A    Cl+(g) → Cl2+(g) + e−
   B    Cl(g) → Cl2+(g) + 2e−
   C    Cl(g) → Cl2−(g) − 2e−
   D    Cl−(g) → Cl2−(g) − e−
(Total for Question = 1 mark)

Q39.
This question is about the elements arsenic to rubidium which have atomic numbers 33 to 37.
The first ionization energies, Em1, of these elements are given in the table.

(a)  Write the equation, with state symbols, which represents the first ionization energy of arsenic.
(2)

(b)  Suggest the formulae of the hydrides of arsenic and selenium.
(2)

(c)  (i)  Complete the electronic configuration for an arsenic and a selenium atom using the electrons-in-boxes notation.
(2)

*(ii)  Explain why the first ionization energy of selenium is lower than that of arsenic.
(2)
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*(d)  Explain why the first ionization energy of krypton is higher than that of selenium.
(2)
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*(e)  Explain why the first ionization energy of rubidium is lower than that of krypton.
(2)
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 (f)  Which of the elements, arsenic to rubidium, is likely to have atoms with the smallest atomic radius?
(1)
 (Total for Question = 13 marks)
Q40.
In atoms, electrons fill up the sub-shells in order of increasing energy.
(a)  Fill in the last two boxes in the table below to show the order in which the next two sub-shells are filled.

(2)
(b)  Electrons in atoms occupy orbitals.

(i)  Explain the term orbital.
(1)
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(ii)  Draw diagrams below to show the shape of an s-orbital and of a p-orbital.
(2)

(c)  State the total number of electrons occupying all the p-orbitals in one atom of chlorine.
(1)
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(d)  State the number of electrons present in an ion of calcium, Ca2+.
(1)
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*(e)  Define the term first ionization energy.
(3)
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 (f)  The ionization energies of sodium, Na, are shown in the table below.
Show with a tick (), in the third row of the table below, all the ionization numbers that involve the removal of an electron from an s-orbital.
(2)

(Total for Question = 12 marks)

Q41.
The first five ionization energies of an element, X, are shown in the table.

What is the mostly likely formula of the oxide that forms when X burns in oxygen?
   A    X2O
   B    XO
   C    X2O3
   D    XO2
(Total for Question = 1 mark)

Q42.
For Period 3 of the Periodic Table, from sodium to argon, what is the trend in the melting temperatures of the elements?
   A    A steady decrease
   B    A steady increase
   C    A decrease to silicon then an increase
   D    An increase to silicon then a decrease
(Total for Question = 1 mark)

Unit 1 - Jun 2014
Q43.
 Which of the following diagrams represents the electrons in the ground state of a boron atom?

(Total for question = 1 mark)

Q44.
 A particle with a single positive charge and with the electronic configuration 1s2 2s2 2p6 is
   A    a sodium ion.
   B    a fluoride ion.
   C    an oxide ion.
   D    a potassium ion.
 (Total for question = 1 mark)

Q45.
 In which of the following series of elements is there an increase in the melting temperatures from left to right?
   A    Na Mg Al
   B    Li  Na  K
   C    B   C   N
   D    Si  P    S
 (Total for question = 1 mark)

Q46.
Naturally occurring samples of potassium contain three isotopes, 39K, 40K and 41K.
(a)  The isotopes can be separated in a mass spectrometer.
(i)  In the diagram below, particles are ionized at A and detected at D.

Name the processes occurring in the mass spectrometer at B and C.
(2)
B  ...................................................................................................................................... 
C  ...................................................................................................................................... 

(ii)  A sample of potassium has the following composition.

Calculate the relative atomic mass of this sample of potassium, giving your answer to two decimal places.
(2)

(iii)  Complete the table below to show the numbers of sub-atomic particles in an atom of each of the isotopes 39K and 41K.
(1)

(iv)  Complete the electronic configuration for an atom of 39K.
(1)
1s2 ........................................................................................................................... 
(v)  Why is potassium placed after argon in the Periodic Table, even though it has a smaller relative atomic mass?
(1)
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*(vi)  Explain why a potassium ion is smaller than a potassium atom.
(2)
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(b)  The type of bonding in potassium is metallic.
Draw a labelled diagram to illustrate the metallic bonding in potassium.
(2)

(c)  The graph shows the variation of first ionization energy with atomic number for six successive elements in the Periodic Table, including potassium. The letters used to label the elements are not their symbols.

(i)  Define the term first ionization energy.
(3)
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 (ii)  Identify, with a reason, which element is potassium.
(2)
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(Total for question = 16 marks)

Q47.
 Nickel is an element in the d-block of the Periodic Table.
(a)  Complete the electronic configuration of a nickel atom using the s, p, d notation.
(1)
1s2 .................................................................................................................... 

(b)  A sample of nickel is made up of three isotopes. The percentage abundances are shown in the table below.

Calculate the relative atomic mass of nickel. Give your answer to two decimal places.
(2)

(c)  Nickel reacts with carbon monoxide, CO, to give the compound nickel carbonyl, Ni(CO)4.
Ni(s) + 4CO(g) → Ni(CO)4(g)
(i)  Calculate the volume of carbon monoxide, in dm3, measured at room temperature and pressure, that is required to react completely with 5.87 g of nickel.
[Relative atomic mass: Ni = 58.7 Molar volume of a gas = 24 dm3 mol−1 at room temperature and pressure.]
(3)

(ii)  Calculate the number of carbon monoxide molecules present in the volume of gas you have calculated in (c)(i). 
[The Avogadro constant, L = 6.02 × 1023 mol−1]
(1)

(d)  Nickel(II) nitrate, Ni(NO3)2, can be made by several different methods.
Method 1
Nickel(II) oxide, NiO, was reacted with dilute nitric acid according to the equation
NiO(s) + 2HNO3(aq) → Ni(NO3)2(aq) + H2O(l)
(i)  Calculate the volume of 2.00 mol dm−3 dilute nitric acid, in cm3, that was required to exactly neutralize 1.494 g of nickel(II) oxide.
Use the relative atomic masses: Ni = 58.7, O = 16.0
(3)

Method 2
A volume of 25.0 cm3 of 2.00 mol dm−3 nitric acid, HNO3, was transferred to a beaker. Solid nickel(II) carbonate, NiCO3, was added until it was in excess.
(ii)  Why was excess nickel(II) carbonate used?
(1)
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(iii)  Why must the beaker be much larger than the volume of acid used?
(1)
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(iv)  Write a balanced equation for the reaction between nickel(II) carbonate and dilute nitric acid, including state symbols.
(2)

*(v)  For Method 2, describe the practical steps that you would take to obtain pure dry crystals of hydrated nickel(II) nitrate, Ni(NO3)2.6H2O, from a mixture of nickel(II) nitrate solution and unreacted solid nickel(II) carbonate.
(4)
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 (Total for question = 18 marks)

Q48.
 This question concerns the Periodic Table.
(a)  An atom of argon has mass number 40. Complete the table below showing the numbers of sub-atomic particles in this atom of argon. Use the Periodic Table as a source of data.
(1)

(b)  An atom of potassium has mass number 39. Explain why argon is placed before potassium in the modern Periodic Table.
(1)
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(c)  In the context of the Periodic Table, explain what is meant by the term periodicity.
(2)
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(d)  The graph shows the variation in melting temperatures of the elements across Period 3 (Na to Ar) of the Periodic Table.

(i)  Name one of the elements above that is composed of simple molecules at room temperature and pressure.
(1)
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(ii)  Silicon has a giant atomic structure. Explain how this structure results in the high melting temperature shown on the graph.
(2)
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(iii)  Explain why the melting temperature of magnesium is higher than that of sodium.
(3)
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 (Total for question = 10 marks)