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.


Erbium, symbol Er, metallic element, whose atomic number is 68. The Swedish chemist Carl Gustav Mosander discovered erbium in 1843. Erbium occurs mostly in the same minerals and in the same areas as dysprosium. One of the rare earth elements, erbium is 43rd in abundance among the elements of the earth's crust. The atomic weight of erbium is 167.26. The element melts at about 1529° C (about 2784° F), boils at about 2868° C (about 5194° F), and has a specific gravity of 9.1.

Metallic erbium has a bright silvery luster. Erbium oxide, is a rose-red compound slowly soluble in many mineral acids, forming a series of rose-colored salts, solutions of which have a sweet, astringent taste. Erbium is used in experimental optical amplifiers that amplify light signals sent along fiber-optic cables (see Fiber Optics).