Ions and ionic bonds

"Atoms sharing electrons" or "atoms joined together" describes covalent bonding and scores zero for an ionic bond. The mark scheme needs both halves: electrostatic attraction (not "sharing", not a vague "joining") and oppositely charged ions (not "atoms"). Name the attraction, and name the ions it acts between.

Diagrams must show the resultant ions — each with the right outer-shell electron count, in square brackets with the charge outside — not an arrow showing an electron jumping across, and not neutral atoms left unrelabelled. Shell sizes and spacing must stay consistent. For $\text{MgCl}_2$ draw two separate chloride ions, one electron to each, not both to one chlorine.

Halogens are non-metals, so candidates extend the "non-metal means covalent" rule to every bond a halogen forms. Bond type depends on both elements: two non-metals give covalent ($\text{Cl}_2$, HCl); a metal with a non-metal gives ionic (NaCl). Chlorine does both, so check its partner before choosing.

Asked to explain a high melting point, "it has strong bonds" or "the particles are close together" does not score. Name the giant lattice, the strong electrostatic attractions between oppositely charged ions, that melting overcomes very many of them throughout the structure, and that this needs a large amount of energy.

The other melting-point error is reaching for the wrong bonding model — describing the strength of covalent bonds within a molecule, or the weak intermolecular forces between molecules, when the question is about an ionic lattice. Keep the three models separate; only the lattice answer earns the marks here.

Saying a solid ionic compound "has no charge" is wrong — it is built entirely from charged ions. What it lacks is mobility: the ions are locked in fixed lattice positions and cannot move to carry charge. Melting or dissolving breaks the lattice down so the same ions become free to move, and only then does it conduct.

After transfer, quote the ion's electronic structure, not the atom's. $\text{Na}^+$ is $2,8$ (not $2,8,1$) because the outer electron has gone; $\text{Cl}^-$ is $2,8,8$ (not $2,8,7$) because one has been gained. Writing the atom's structure beside an ion symbol loses the mark even when the charge itself is right.