Mercury, Hg, one of only two liquid elements in the whole periodic table and the only metal liquid at room temperature. It was also the element that drove hatters mad when they breathed in its vapours!
I like Iridium – Ir. You can make pretty fluorescent compoounds with Ir(III) ions, which can luminesce blue, green, yellow, orange, red and even in the near-IR range, if you change the ligands coordinated to the metal complex.
Comments