Europium

Europium is atom number 63 — every Europium atom has exactly 63 protons in its center, and that number is what makes it Europium and nothing else. Its symbol is Eu. At room temperature it is a solid.

Europium is a chemical element with symbol Eu and atomic number 63. It was isolated in 1901 and is named after the continent of Europe. It is a moderately hard, silvery metal which readily oxidizes in air and water.

Summary from the source dataset, derived from Wikipedia (CC BY-SA 3.0) · original article

Europium sits in period 6, group 3 of the f-block. Its 63 electrons fill shells of 2, 8, 18, 25, 8, 2 — written as [Xe] 4f7 6s2. Its electronegativity is 1.2 on the Pauling scale, and pulling the first electron off takes 547.1 kJ/mol. The outermost shell holds 2 electrons — the ones that do all the chemistry.

Full configuration: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f7
Ionization energies (kJ/mol): 547.1, 1085, 2404, 4120
Electron affinity: 11.2 kJ/mol · Electronegativity (Pauling): 1.2
Density: 5.264 g/cm³ · melts 1099 K · boils 1802 K

Values exactly as published — see where the data comes from.