Past exam of the chemistry course of the year 4 of the natural sciences course of the University of Cambridge / 2022 / Paper 2 / Section H / 33 / b / iv / Solution

The revised question page explicitly gives the cluster as $\{\mathrm{G}{\mathrm{a}}_{22}[\mathrm{N}(\mathrm{SiM}{\mathrm{e}}_3{)}_2{]}_{10}{\}}^{2-}$. Its charge supplies two electrons, soa jellium shell closure, through 1G. The reported structure has a Ga atom inside an eleven-atom Ga shell, with ten further ligand-bearing Ga units outside that core.^[ref]

The canonical exam copy omits the 2− charge. Taken literally as a neutral formula it gives 56 electrons, which is not a listed shell closure; assigning 58 without identifying this difference would be unjustified. The revised public source resolves the discrepancy rather than requiring an invented charge.^[ref]