# Why is the nomenclature for Mercury (I) Fluoride Hg2F2 and not HgF?

Dec 3, 2016

Because mercurous ion is the $H {g}_{2}^{2 +}$ ion...........The empirical formula of mercurous halide may be $H g X$, but its molecular formula is $H {g}_{2} {X}_{2}$.

#### Explanation:

And thus $\text{mercurous halide}$ is $H {g}_{2} {X}_{2}$; and $\text{mercuric halide}$ is $H g {X}_{2}$. As is common with $\text{ous}$ versus $\text{ic}$ endings, the $\text{ic}$ denotes the higher oxidation state.

In $H g {X}_{2}$ the metal displays a formal $+ I I$ oxidation state; in $H {g}_{2} {X}_{2}$ the metal displays a formal $+ I$ oxidation state. Where there is an $\text{element-element bond}$, as here in $H g - H g$, or in a $C - C$ linkage, the 2 electrons of the bond are assumed to be distributed EQUALLY to the bound atoms. When we assign oxidation states for $\text{element-heteroelement bonds}$, the most electronegative atom gets the 2 electrons from the bond.

And thus for $H O - C {R}_{3}$, we get formally $H {O}^{-}$ and ""^(+)CR_3. The ipso carbon in ""^(+)CR_3 has a FORMAL $C \left(+ I\right)$ oxidation state.

I write $\text{formal}$ guardedly. Of course with such designations, the assignment of oxidation number is very much a formalism, a practice with little fundamental significance, but there is utility in assigning oxidation numbers for balancing redox reactions.