Thorium (symbol Th, atomic number 90) is a weakly radioactive metal explored as a nuclear fuel. It is classified as a actinide and sits in the actinide series (f-block), period 7 of the periodic table.
Overview
Thorium is the chemical element with atomic number 90 and the symbol Th. With a standard atomic weight of [232], it is a actinide. In the periodic table it occupies the actinide series (f-block) and period 7, and under standard conditions it is normally a solid. Thorium is a weakly radioactive metal explored as a nuclear fuel.
Atomic structure
An atom of Thorium has 90 protons in its nucleus and, when neutral, 90 electrons arranged in the configuration [Rn] 6d2 7s2. Thorium has no stable isotope; the value [232] refers to the mass number of its most stable or most commonly produced isotope.
Discovery and place in the table
Thorium was discovered in 1829 by Jöns Jacob Berzelius. It follows Actinium (Ac) and precedes Protactinium (Pa) in order of atomic number.
| Atomic number | 90 |
|---|---|
| Symbol | Th |
| Atomic mass | [232] |
| Category | Actinide |
| Group | — |
| Period | 7 |
| Electron configuration | [Rn] 6d2 7s2 |
| Phase at STP | Solid |
| Discovered | 1829 (Jöns Jacob Berzelius) |