# Reasons for low melting point of gallium

J.D. Lee writes in Concise Inorganic Chemistry:

Gallium has an unusual structure. Each atom has one closest neighbor at a distance of 2.43 Å.

This remarkable structure tends towards discrete diatomic molecules rather than a metallic structure. This accounts for the incredibly low melting point of gallium at 30 °C.

That's not all, this surprised me as well:

Note that the boiling point for Ga is in line with the others, whereas its melting point is not. The very low melting point is due to the unusual crystal structure, but the structure no longer exists in the liquid.

Why does gallium exist as diatomic units, that too in a solid crystal, instead of forming the usual metallic crystal structure? And why not in liquid state (where it seems to be more free to make diatomic molecules)?

I might guess that $$\ce{Ga2}$$ might form stable MOs, but why do the other members of group 13 abstain from such behavior?

It is quite weird to see an element in the middle of a group staging a drama of exceptions like this, it's usually the 2nd period elements which do that.

For your interest, I quote a paragraph from a book "Handbook of Nanophysics: Nanoparticles and Quantum Dots" by Klaus D. Sattler (Ed.). Section 12-8. I don't think people know the reason as to why Ga likes to exist as a dimer (as you know $$\ce{S}$$ is $$\ce{S8}$$ and so on).