From Citizendium, the Citizens' Compendium
Yttrium is a chemical element, having the chemical symbol Y. Its atomic number (the number of protons) is 39. It has a standard atomic weight of 88.9059 g•mol −1 and is a solid in its elemental form.
Yttrium is considered to be a member of the "Transition metal" class of element. At a pressure of 101.325 kPa, it has a boiling point of 3,345 °C and a melting point of 1,522 °C.
It has some applications in nuclear power reactors, especially those whose weight must be minimized. Yttrium is a component of the semiconductor laser material, YAG (yttrium aluminum garnet).