Astatine

Astatine is atom number 85 — every Astatine atom has exactly 85 protons in its center, and that number is what makes it Astatine and nothing else. Its symbol is At. At room temperature it is a solid.

Astatine is a very rare radioactive chemical element with the chemical symbol At and atomic number 85. It occurs on Earth as the decay product of various heavier elements. All its isotopes are short-lived; the most stable is astatine-210, with a half-life of 8.1 hours.

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

Astatine sits in period 6, group 17 of the p-block. Its 85 electrons fill shells of 2, 8, 18, 32, 18, 7 — written as [Xe] 4f14 5d10 6s2 6p5. Its electronegativity is 2.2 on the Pauling scale, and pulling the first electron off takes 899.003 kJ/mol. The outermost shell holds 7 electrons — the ones that do all the chemistry.

Full configuration: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p5
Ionization energies (kJ/mol): 899.003
Electron affinity: 233 kJ/mol · Electronegativity (Pauling): 2.2
Density: 6.35 g/cm³ · melts 575 K · boils 610 K

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