Symbol

U

Atomic Number

92

Atomic Mass

238.0289

Family

Actinide Pronunciation

yUH-RAY-nee-um

Overview

Uranium is the heaviest and last naturally occurring element in the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. Uranium occurs near the beginning of the actinide family. The actinide family consists of elements with atomic numbers 90 through 103.

At one time, uranium was considered to be a relatively unimportant element. It had a few applications in the making of stains and dyes, in producing specialized steels, and in lamps. But annual sales before World War I I (1939-45) amounted to no more than a few hundred metric tons of the metal and its compounds.

Then, a dramatic revolution occurred. Scientists discovered that one form of uranium will undergo nuclear fission. Nuclear fission is the process in which the nuclei of large atoms break apart. Large amounts of...