Potassium

Potassium is atom number 19 — every Potassium atom has exactly 19 protons in its center, and that number is what makes it Potassium and nothing else. Its symbol is K. At room temperature it is a solid.

Potassium is a chemical element with symbol K (derived from Neo-Latin, kalium) and atomic number 19. It was first isolated from potash, the ashes of plants, from which its name is derived. In the Periodic table, potassium is one of seven elements in column (group) 1 (alkali metals):they all have a single valence electron in their outer electron shell, which they readily give up to create an atom with a positive charge - a cation, and combine with anions to form salts.

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

Potassium sits in period 4, group 1 of the s-block. Its 19 electrons fill shells of 2, 8, 8, 1 — written as [Ar] 4s1. Its electronegativity is 0.82 on the Pauling scale, and pulling the first electron off takes 418.8 kJ/mol. The outermost shell holds 1 electron — the ones that do all the chemistry.

Full configuration: 1s2 2s2 2p6 3s2 3p6 4s1
Ionization energies (kJ/mol): 418.8, 3052, 4420, 5877, 7975, 9590, 11343, 14944 … (19 published)
Electron affinity: 48.383 kJ/mol · Electronegativity (Pauling): 0.82
Density: 0.862 g/cm³ · melts 336.7 K · boils 1032 K

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