Promethium

Promethium is atom number 61 — every Promethium atom has exactly 61 protons in its center, and that number is what makes it Promethium and nothing else. Its symbol is Pm. At room temperature it is a solid.

Promethium, originally prometheum, is a chemical element with the symbol Pm and atomic number 61. All of its isotopes are radioactive; it is one of only two such elements that are followed in the periodic table by elements with stable forms, a distinction shared with technetium. Chemically, promethium is a lanthanide, which forms salts when combined with other elements.

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

Promethium sits in period 6, group 3 of the f-block. Its 61 electrons fill shells of 2, 8, 18, 23, 8, 2 — written as [Xe] 4f5 6s2. Its electronegativity is 1.13 on the Pauling scale, and pulling the first electron off takes 540 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 4f5
Ionization energies (kJ/mol): 540, 1050, 2150, 3970
Electron affinity: 12.45 kJ/mol · Electronegativity (Pauling): 1.13
Density: 7.26 g/cm³ · melts 1315 K · boils 3273 K

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