Mercurous ion is written as `Hg_(2)^(2+)` whereas cuprous ion is written as `Cu^(+)` . Explain.

Explanation

The electronic configuration of Hg(I) is `[Xe]4f^(14)5d^(10)6s^1 ` It has one unpaired electron in the valence 68-subshell. Because of the presence of unpaired electron, it is expected to be paramagnetic but actually Hg(I) compounds are diamagnetic. This can be explained by assuming that the singly filled 6s-orbitals of two `Hg^+` ions overlap to form `Hg^(+) - Hg^(+)` covalent bond. Therefore,`Hg^+` ion exists as dimeric species `Hg_2^(2+)` . On the other hand, Cu(I) ion has electronic configuration : `[Ar] 3d^10` . It has no unpaired electron to form dimeric `Cu_2^(2+)` species and therefore , it exists as `Cu^+` ion.