Mercurous ion exists as `Hg_(2)^(2+)`. Explain.

Explanation

`Hg^(+)` has 1 unpaired electron (electronic configuration : `[Xe]4f^(14)5d^(10)6s^(1)`) in the 6s - orbital which indicates that Hg(I) compounds should be paramagnetic but are found to be diamagnetic. This is because, two 6s - orbitals of two `Hg^(+)` ions overlap with one another and forms a covalent `(sigma)` bond (Hg - Hg). Hence, mercurous ion exists as a dimer `(Hg_(2)^(2+))`. [Note : Cuprous ion `([Ar]3d^(10))` does not have any unpaired electron and does not exist as a dimer `(Cu_(2)^(2+))` but as `Cu^(+)` ion].