Why is the dissociation of Hg2Br2 not 2Hg2+ and 2Br-?

Question

I read that it is expressed as: Hg₂Br₂(s) ⇌ Hg₂²⁺(aq) + 2Br¯(aq)

Why is there not a 2 in front of the Hg?

Answer 1

If it was Hg²⁺ the formula of the salt would be HgBr₂, not Hg₂Br₂ . The very fact that the formula is not in lowest terms for a salt is an indicator that there is something odd going on. (Another example is sodium peroxide: Na₂O₂ )

It turns out that Mercury(I) is not Hg⁺, but Hg₂²⁺ a diatomic ion. The compound given is Mercury(I) bromide.