Symbol

Pm

Atomic Number

61

Atomic Mass

144.9128

Family

Lanthanide (Rare Earth Metal) Pronunciation

pruh-MEE-thee-um

Overview

Promethium is one of the most fascinating of all chemical elements. It has never been found on the Earth's surface. Scientists know of it only because it can be prepared artificially in particle accelerators ("atom smashers") and in other unusual reactions. Its existence was predicted as early as 1902, but its discovery was not confirmed until 1945.

All of the known isotopes of promethium are radioactive. That is, they break down and give off radiation spontaneously.

At one time, promethium was strictly a laboratory curiosity. Today, however, it has a number of practical industrial applications.

Discovery and Naming

In the late 1860s, Russian chemist Dmitri Mendeleev (1834- 1907) discovered the periodic law. The periodic law provides a way of organizing the chemical elements to show how they are related to each other. It is usually represented by...