Melting of gallium is the lowest in the group. Why?
Answers
Gallium metal is somewhat anomalous because it's melting point is very low (Tm = 303 K) but its boiling point is relatively high Tb = 2477 K. That is say that its liquid state has got a very large stability range. Also its pressure variation of melting point is negative. My hand-waving explanation is that Ga has several competing structures that have almost the same energy close to its melting temperature and therefore just below Tm the solid transforms continuously from one structure to the other competing structures and therefore melts. The crystal structure of Ga at ambient conditions is different from the usual metallic structure. In the alpha-Ga structure the Ga atom has a neighbor at a short distance and six other Ga atoms somewhat further away. So there is some sort of dimerization. I have plans to do neutron scattering experiments on Ga close to its melting point both in the solid and liquid state.