1. 1
   Lithium, beryllium and magnesium are light metals used in alloys for aircraft and batteries. Their melting points are: lithium 181 °C, beryllium 1287 °C and magnesium 650 °C. Their ionic radii are Li⁺ 76 pm, Be²⁺ 45 pm and Mg²⁺ 72 pm.

   (a)

   Which lists the three metals in order of increasing strength of metallic bonding?

   [1 mark]

   • ALi < Mg < Be
   • BBe < Mg < Li
   • CMg < Li < Be
   • DLi < Be < Mg

   (b)

   Which factor is mainly responsible for magnesium having stronger metallic bonding than lithium?

   [1 mark]

   • AMg²⁺ is much smaller than Li⁺
   • BMg²⁺ has a higher charge and magnesium delocalises two electrons per atom
   • CMagnesium has more electron shells than lithium
   • DMagnesium atoms are held by covalent bonds as well as metallic bonds

   (c)

   Explain why beryllium has a higher melting point than magnesium.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Iron (Z = 26) has the electron configuration [Ar]4s²3d⁶ and melts at 1538 °C. Calcium (Z = 20) has the configuration [Ar]4s² and melts at 842 °C. Both metals conduct electricity in the solid and liquid states.

   (a)

   Which electrons of an iron atom contribute to the delocalised electrons in the metal?

   [1 mark]

   • AThe 4s electrons only
   • BThe 3d electrons only
   • CThe 4s and 3d electrons
   • DAll the electrons in the third and fourth main energy levels

   (b)

   Which statement best explains why iron has a much higher melting point than calcium?

   [1 mark]

   • AIron has covalent bonds between its atoms in addition to metallic bonds
   • BIron atoms are larger than calcium atoms, so more electrons are delocalised
   • CIron has more protons, so the London forces between its atoms are stronger
   • DIron delocalises 3d as well as 4s electrons, so there are more delocalised electrons per atom and a stronger attraction to the cations

   (c)

   Explain, with reference to its electron configuration, why iron is a good electrical conductor.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The melting points of the period 4 metals from potassium to zinc, in °C, are: potassium 63, calcium 842, scandium 1541, titanium 1668, vanadium 1910, chromium 1907, manganese 1246, iron 1538, cobalt 1495, nickel 1455, copper 1085 and zinc 420. Zinc has the configuration [Ar]3d¹⁰4s² and forms only the Zn²⁺ ion (radius 74 pm); the Ca²⁺ ion has a radius of 100 pm. Nickel has the configuration [Ar]3d⁸4s².

   (a)

   Compare the melting points of scandium to nickel with those of potassium and calcium, and explain the difference.

   [3 marks]

   (b)

   Zinc melts at 420 °C, lower than both nickel and calcium. Suggest why, and evaluate how well the simple charge-and-radius model explains zinc's melting point.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A component near a jet engine must remain solid and strong at 700 °C, be as light as possible and be shaped by pressing sheets of metal. Three candidate metals are: magnesium, [Ne]3s², melting point 650 °C, density 1.74 g cm⁻³; aluminium, [Ne]3s²3p¹, melting point 660 °C, density 2.70 g cm⁻³; titanium, [Ar]3d²4s², melting point 1668 °C, density 4.51 g cm⁻³. Steel, the usual alternative, has a density of about 7.9 g cm⁻³.

   (a)

   Explain why titanium has a much higher melting point than magnesium and aluminium, referring to electron configurations and metallic bonding.

   [6 marks]

   (b)

   Evaluate which of the three metals is most suitable for the component, using the data and your knowledge of metallic bonding.

   [6 marks]

   Total for question 4: 12 marks

End of questions