Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Cerium, symbol Ce, soft, gray metallic element that is the most abundant of the rare earth elements. Cerium is in the lanthanide series of the periodic table (see Periodic Law); its atomic number is 58.

Cerium was discovered in 1803 by the Swedish chemists Baron Jöns Jakob Berzelius and Wilhelm Hisinger, and in the same year, independently, by the German chemist Martin Heinrich Klaproth; the pure metallic element was not isolated until 1875.

Cerium ranks 26th in natural abundance among the elements in the earth's crust. It occurs with other rare earth metals in monazite, which is found widely distributed worldwide, and bastnasite, found in southern California. It also occurs in the minerals cerite, found in Sweden, and allanite, found in Greenland and New York state. Cerium is the only one of the rare earth metals that can be easily separated from the others. Cerium melts at 798° C (1468° F), boils at about 3443° C (about 6229° F), and has a specific gravity of 6.77; the element has an atomic weight of 140.12.

Metallic cerium is found chiefly in an alloy with iron that composes the flints used in cigarette lighters. Ceric oxide was formerly employed in the manufacture of gas mantles. Compounds of cerium are employed in small quantities in the manufacture of glass, ceramics, arc-lamp electrodes, and photoelectric cells. Cerous nitrate has been used medicinally in the treatment of seasickness and chronic vomiting. Ceric sulfate is used in analytic-chemistry laboratories as an oxidizing agent.