Antimony

Antimony is atom number 51 — every Antimony atom has exactly 51 protons in its center, and that number is what makes it Antimony and nothing else. Its symbol is Sb. At room temperature it is a solid.

Antimony is a chemical element with symbol Sb (from Latin:stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient times and were used for cosmetics; metallic antimony was also known, but it was erroneously identified as lead upon its discovery.

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

Antimony sits in period 5, group 15 of the p-block. Its 51 electrons fill shells of 2, 8, 18, 18, 5 — written as [Kr] 4d10 5s2 5p3. Its electronegativity is 2.05 on the Pauling scale, and pulling the first electron off takes 834 kJ/mol. The outermost shell holds 5 electrons — the ones that do all the chemistry.

Full configuration: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p3
Ionization energies (kJ/mol): 834, 1594.9, 2440, 4260, 5400, 10400
Electron affinity: 101.059 kJ/mol · Electronegativity (Pauling): 2.05
Density: 6.697 g/cm³ · melts 903.78 K · boils 1908 K

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