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.


Gallium, symbol Ga, metallic element that remains in the liquid state over a wider range of temperatures than any other element. Gallium is in group 13 (or IIIa) of the periodic table; its atomic number is 31.

Gallium was discovered spectroscopically by the French chemist Paul Émile Lecoq de Boisbaudran in 1875; a year later he isolated the element in its metallic state. Gallium is blue-gray in color as a solid and silvery as a liquid. It is one of the few metals that are liquid near room temperature. It can be supercooled; like water, it expands upon freezing. The element is about 34th in order of abundance in Earth’s crust. Gallium melts at 30°C (86°F), boils at about 2403°C (about 4357°F), and has a specific gravity of 5.9; the atomic weight of the element is 69.72.

Gallium occurs in small quantities in some varieties of zinc blende, bauxite, pyrite, magnetite, and kaolin. Gallium resembles aluminum in forming trivalent salts and oxides; it also forms a few monovalent and divalent compounds. The low melting point and high boiling point of the metal are used to advantage in high-temperature thermometers. Certain gallium compounds are excellent semiconductors and have been extensively used in rectifiers, transistors, photoconductors, and laser and maser diodes.