Metallic hydrogen

Metallic hydrogen results when hydrogen is sufficiently compressed and undergoes a phase change; it is an example of degenerate matter. Solid metallic hydrogen consists of a crystal lattice of atomic nuclei (namely, protons), with a spacing which is significantly smaller than a Bohr radius. Indeed, the spacing is more comparable with an electron wavelength (see De Broglie wavelength). The electrons are unbound and behave like the conduction electrons in a metal. As is the dihydrogen molecule H2, metallic hydrogen is an allotrope. In liquid metallic hydrogen protons do not have lattice ordering, that system is a liquid of protons and electrons.