Iodine

Iodine is atom number 53 — every Iodine atom has exactly 53 protons in its center, and that number is what makes it Iodine and nothing else. Its symbol is I. At room temperature it is a solid.

Iodine is a chemical element with symbol I and atomic number 53. The name is from Greek ἰοειδής ioeidēs, meaning violet or purple, due to the color of iodine vapor. Iodine and its compounds are primarily used in nutrition, and industrially in the production of acetic acid and certain polymers.

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

Iodine sits in period 5, group 17 of the p-block. Its 53 electrons fill shells of 2, 8, 18, 18, 7 — written as [Kr] 4d10 5s2 5p5. Its electronegativity is 2.66 on the Pauling scale, and pulling the first electron off takes 1008.4 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 5p5
Ionization energies (kJ/mol): 1008.4, 1845.9, 3180
Electron affinity: 295.1531 kJ/mol · Electronegativity (Pauling): 2.66
Density: 4.933 g/cm³ · melts 386.85 K · boils 457.4 K

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