Lanthanum is the third element in Row 6 of the periodic table. It is sometimes classified as a rare earth element, a group of elements that follow it in Row 6 and are also known as the lanthanides. Lanthanum's atomic number is 57, its atomic mass is 138.9055, and its chemical symbol is La.

Properties

Lanthanum is a white metal that is both ductile and malleable. It is relatively soft and can be cut with a sharp knife. The element's melting point is 1,688°F (920°C), its boiling point is 6,249°F (3,454°C), and its density is about 6.18 grams per cubic centimeter. Lanthanum is chemically very active, reacting with both cold water and most acids. It also reacts with oxygen in moist air.

Occurrence and Extraction

Lanthanum is a relatively common element with an abundance of about 18 parts per million in the Earth's crust. Although it is about as abundant as copper and zinc, it is much more difficult to obtain than those two elements. Copper and zinc often occur in large deposits that are easily mined, while lanthanum occurs in a variety of minerals that are spread widely throughout the earth. Its most common minerals are monazite, bastnasite, and cerite. Lanthanum is separated from other rare earth elements by an extended series of processes based on the differential solubility of the elements' compounds.

Discovery and Naming

Credit for the discovery of lanthanum is usually given to the Swedish chemist Carl Gustav Mosander. Mosander was very much interested in an unusual black rock found near the town of Bastnas, Sweden, in the 1830s. Over the next 60 years, chemists discovered a total of seven new elements in that rock, one of them being lanthanum, discovered in 1839. The element was named after the Greek word lanthanein, meaning "to hide."

Uses

One of the oldest use of lanthanum metal is in the production of misch metal, an alloy that produces sparks when struck. Misch metal is used to make the flint in cigarette lighters. Compounds of lanthanum are used to make phosphors, special kinds of glass, and optical fibers.