Terbium

Terbium is atom number 65 — every Terbium atom has exactly 65 protons in its center, and that number is what makes it Terbium and nothing else. Its symbol is Tb. At room temperature it is a solid.

Terbium is a chemical element with symbol Tb and atomic number 65. It is a silvery-white rare earth metal that is malleable, ductile and soft enough to be cut with a knife. Terbium is never found in nature as a free element, but it is contained in many minerals, including cerite, gadolinite, monazite, xenotime and euxenite.

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

Terbium sits in period 6, group 3 of the f-block. Its 65 electrons fill shells of 2, 8, 18, 27, 8, 2 — written as [Xe] 4f9 6s2. Its electronegativity is 1.1 on the Pauling scale, and pulling the first electron off takes 565.8 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 4f9
Ionization energies (kJ/mol): 565.8, 1110, 2114, 3839
Electron affinity: 112.4 kJ/mol · Electronegativity (Pauling): 1.1
Density: 8.23 g/cm³ · melts 1629 K · boils 3396 K

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