Thorium

Thorium is atom number 90 — every Thorium atom has exactly 90 protons in its center, and that number is what makes it Thorium and nothing else. Its symbol is Th. At room temperature it is a solid.

Thorium is a chemical element with symbol Th and atomic number 90. A radioactive actinide metal, thorium is one of only two significantly radioactive elements that still occur naturally in large quantities as a primordial element (the other being uranium). It was discovered in 1828 by the Norwegian Reverend and amateur mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns Jakob Berzelius, who named it after Thor, the Norse god of thunder.

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

Thorium sits in period 7, group 3 of the f-block. Its 90 electrons fill shells of 2, 8, 18, 32, 18, 10, 2 — written as [Rn] 6d2 7s2. Its electronegativity is 1.3 on the Pauling scale, and pulling the first electron off takes 587 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 4f14 5d10 6p6 7s2 6d2
Ionization energies (kJ/mol): 587, 1110, 1930, 2780
Electron affinity: 112.72 kJ/mol · Electronegativity (Pauling): 1.3
Density: 11.724 g/cm³ · melts 2023 K · boils 5061 K

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