Barium

Barium is atom number 56 — every Barium atom has exactly 56 protons in its center, and that number is what makes it Barium and nothing else. Its symbol is Ba. At room temperature it is a solid.

Barium is a chemical element with symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Because of its high chemical reactivity barium is never found in nature as a free element.

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

Barium sits in period 6, group 2 of the s-block. Its 56 electrons fill shells of 2, 8, 18, 18, 8, 2 — written as [Xe] 6s2. Its electronegativity is 0.89 on the Pauling scale, and pulling the first electron off takes 502.9 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
Ionization energies (kJ/mol): 502.9, 965.2, 3600
Electron affinity: 13.954 kJ/mol · Electronegativity (Pauling): 0.89
Density: 3.51 g/cm³ · melts 1000 K · boils 2118 K

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