1. 1
   Sodium, magnesium and aluminium are consecutive metals in period 3. Their melting points are 98 °C, 650 °C and 660 °C respectively. The radii of their ions are Na⁺ 102 pm, Mg²⁺ 72 pm and Al³⁺ 54 pm.

   (a)

   Which statement best describes the bonding in solid magnesium?

   [1 mark]

   • AShared pairs of electrons between neighbouring magnesium atoms
   • BElectrostatic attraction between a lattice of Mg²⁺ ions and delocalised electrons
   • CElectrostatic attraction between a lattice of positive ions and negative ions
   • DLondon (dispersion) forces between neighbouring magnesium atoms

   (b)

   Which row correctly compares aluminium with sodium?

   [1 mark]

   • AAl³⁺ has a higher charge and a larger radius, and aluminium contributes more delocalised electrons per atom
   • BAl³⁺ has a smaller radius, but both metals contribute one delocalised electron per atom
   • CAl³⁺ has a lower charge density, but aluminium contributes more delocalised electrons per atom
   • DAl³⁺ has a higher charge, a smaller radius and aluminium contributes more delocalised electrons per atom

   (c)

   Explain why magnesium has a much higher melting point than sodium.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Copper is drawn into thin wires for electrical cables and pressed into sheets to make the bases of saucepans. Solid copper conducts electricity, but solid copper(II) chloride, CuCl₂, does not. When a copper sheet is hammered it changes shape rather than shattering.

   (a)

   Which particles carry the electric charge when a potential difference is applied across a copper wire?

   [1 mark]

   • ADelocalised electrons moving towards the positive terminal
   • BCopper ions moving towards the negative terminal
   • CCopper atoms moving through the lattice
   • DCopper ions and electrons moving in opposite directions

   (b)

   Which explanation accounts for copper changing shape rather than shattering when hammered?

   [1 mark]

   • AThe covalent bonds between copper atoms bend without breaking
   • BLayers of cations are brought next to each other and repel, so they slide apart
   • CLayers of cations slide over one another, and the non-directional attraction to the delocalised electrons is maintained
   • DThe weak intermolecular forces between copper atoms allow them to move freely

   (c)

   Explain why solid copper conducts electricity but solid copper(II) chloride does not.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The melting points of the group 1 metals are: lithium 181 °C, sodium 98 °C, potassium 63 °C, rubidium 39 °C and caesium 28 °C. Their ionic radii are Li⁺ 76 pm, Na⁺ 102 pm, K⁺ 138 pm, Rb⁺ 152 pm and Cs⁺ 167 pm. Calcium, in group 2, melts at 842 °C and the Ca²⁺ ion has a radius of 100 pm.

   (a)

   Describe and explain the trend in melting point down group 1.

   [3 marks]

   (b)

   A student claims that the strength of metallic bonding depends only on the radius of the metal ion. Evaluate this claim using the data for sodium and calcium.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An engineer is choosing a metal for overhead power cables, which must be light, conduct electricity well, stay solid when the cable warms up in use and be drawn easily into long wires. Data at 20 °C: aluminium — density 2.70 g cm⁻³, electrical conductivity 3.8 × 10⁷ S m⁻¹, melting point 660 °C; copper — density 8.96 g cm⁻³, conductivity 6.0 × 10⁷ S m⁻¹, melting point 1085 °C; sodium — density 0.97 g cm⁻³, conductivity 2.1 × 10⁷ S m⁻¹, melting point 98 °C, reacts rapidly with oxygen and water. For cables of equal electrical resistance and equal length, the mass of cable is proportional to density ÷ conductivity.

   (a)

   Explain, using the metallic model, why all three metals conduct electricity and heat, and why aluminium is a better electrical conductor than sodium.

   [6 marks]

   (b)

   Evaluate the suitability of each of the three metals for overhead power cables, using the data and the metallic model.

   [6 marks]

   Total for question 4: 12 marks

End of questions