Scandium

Scandium is atom number 21 — every Scandium atom has exactly 21 protons in its center, and that number is what makes it Scandium and nothing else. Its symbol is Sc. At room temperature it is a solid.

Scandium is a chemical element with symbol Sc and atomic number 21. A silvery-white metallic d-block element, it has historically been sometimes classified as a rare earth element, together with yttrium and the lanthanoids. It was discovered in 1879 by spectral analysis of the minerals euxenite and gadolinite from Scandinavia.

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

Scandium sits in period 4, group 3 of the d-block. Its 21 electrons fill shells of 2, 8, 9, 2 — written as [Ar] 3d1 4s2. Its electronegativity is 1.36 on the Pauling scale, and pulling the first electron off takes 633.1 kJ/mol. The outermost shell holds 2 electrons — the ones that do all the chemistry.

Full configuration: 1s2 2s2 2p6 3s2 3p6 4s2 3d1
Ionization energies (kJ/mol): 633.1, 1235, 2388.6, 7090.6, 8843, 10679, 13310, 15250 … (21 published)
Electron affinity: 18 kJ/mol · Electronegativity (Pauling): 1.36
Density: 2.985 g/cm³ · melts 1814 K · boils 3109 K

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