Table 9.1 shows the melting points and relative electrical conductivities of three elements. Table 9.1 | | carbon (graphite) | magnesium | phosphorus |---|---|---|--- | melting point /°C | 3652 | 649 | 44 | relative electrical conductivity of solid | good | good | poor Use ideas about structure and bonding to explain:

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2023). The mark or mark type is shown in brackets.

1. [1] (a)(i) magnesium (has a high melting point because) has a giant metallic lattice and sea of delocalised electrons
2. [1] (a)(i) strong bonding between the ions and delocalised electrons / strong bonding between ions and 'sea' of electrons
3. [1] (a)(i) phosphorus (has a low melting point because) there are weak forces between the molecules / phosphorus has weak intermolecular forces
4. [1] (a)(ii) graphite has (delocalised) mobile electrons / (delocalised) electrons which can move
5. [1] (a)(ii) phosphorus has no mobile electrons / charge carriers
6. [1] (b) M1 diamond has a giant structure of covalent bonds
7. [1] (b) M2 diamond has strong bonding between all the atoms
8. [1] (c) division by correct relative atomic mass e.g. P = 20.2/31, O = 10.4/16, Cl = 69.4/35.5
9. [1] (c) division by lowest value to get correct answer of POCl₃