Symbol

La

Atomic Number

57

Atomic Mass

138.9055

Family

Group 3 (Iiib) Transition Metal Pronunciation

LAN-tha-num

Overview

Lanthanum is the third element in Row 6 of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. Lanthanum is a transition element in Group 3 (IIIB) of the periodic table. Lanthanum's position makes it one of the transition metals. The transition metals are found in the center of the periodic table, in Groups 3 through 12.

Lanthanum can also be classified as a rare earth element. The rare earth elements are the 15 elements that make up Row 6 of the periodic table. That group of elements is also called the lanthanides. Either way of classifying Lanthanum is acceptable to most chemists.

Lanthanum was first discovered by Swedish chemist Carl Gustav Mosander (1797-1858) in 1839. This discovery was the first chapter in a long and interesting story. At the end...