Europium is a chemical element with the symbol Eu and atomic number 63. Europium is the most reactive lanthanide by far, having to be stored under an inert fluid to protect it from atmospheric oxygen or moisture.
Phase at STP： solid
Melting point： 1099 K (826 °C, 1519 °F)
Boiling point： 1802 K (1529 °C, 2784 °F)
Density (near r.t.)： 5.264 g/cm3
when liquid (at m.p.)： 5.13 g/cm3
Heat of fusion： 9.21 kJ/mol
Heat of vaporization： 176 kJ/mol
Molar heat capacity： 27.66 J/(mol·K)
Europium has no significant biological role and is relatively non-toxic compared to other heavy metals. Most applications of europium exploit the phosphorescence of europium compounds. Europium is one of the rarest of the rare earth elements on Earth.