Symbol

Th

Atomic Number

90

Atomic Mass

232.0381

Family

Actinide Pronunciation

THOR-ee-um

Overview

Thorium is a member of the actinide family. The actinide elements are located in Row 7 of the periodic table. They have atomic numbers between 90 and 103. The periodic table is a chart that shows how chemical elements are related to one another. The actinide series is named for element 89, actinium, which is sometimes included in the actinide family.

Thorium was discovered in 1828 by Swedish chemist Jons Jakob Berzelius (1779-1848). At the time, Berzelius did not realize that thorium was radioactive. That was discovered 70 years later, in 1898, by Polish-French physicist Marie Curie (1867-1934) and English chemist Gerhard C. Schmidt (1864- 1949).

Thorium is a relatively common element with few commercial applications. There is some hope that it can someday be used in nuclear power plants, in which nuclear reactions are used to generate electricity.

Discovery and Naming

In 1815, Berzelius was...