Lanthanum

Lanthanum is atom number 57 — every Lanthanum atom has exactly 57 protons in its center, and that number is what makes it Lanthanum and nothing else. Its symbol is La. At room temperature it is a solid.

Lanthanum is a soft, ductile, silvery-white metallic chemical element with symbol La and atomic number 57. It tarnishes rapidly when exposed to air and is soft enough to be cut with a knife. It gave its name to the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table:it is also sometimes considered the first element of the 6th-period transition metals.

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

Lanthanum sits in period 6, group 3 of the f-block. Its 57 electrons fill shells of 2, 8, 18, 18, 9, 2 — written as [Xe] 5d16s2. Its electronegativity is 1.1 on the Pauling scale, and pulling the first electron off takes 538.1 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 5d1
Ionization energies (kJ/mol): 538.1, 1067, 1850.3, 4819, 5940
Electron affinity: 53 kJ/mol · Electronegativity (Pauling): 1.1
Density: 6.162 g/cm³ · melts 1193 K · boils 3737 K

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