HYDROGEN, THE FIRST ALKALI-METAL

We examine the density-dependent metal-nonmetal transition (MNMT) for the Group 1 elements hydrogen, rubidium and caesium. Remarkably, the e xperimentally observed metallization densities agree closely with thos e predicted from the 1927 classical theory of K. F. Herzfeld, which ou tlines the critical conditions necessary for the metallization of any element of the periodic system. The metallization densities of the alk ali metal elements are also consistent with the quantum mechanical the ory of the MNMT, as first set out by Sir Nevill Mott.