Except for boron (B), the elements that make up Group 3A of the periodic table—boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl)—are all metals. Boron is never found in a pure state in nature but always combined with oxygen, especially in the mineral borax, which is used as a mild antiseptic, detergent, and water-softener. Borax is also used in making porcelain enamel, glaze for dishes, and high-strength glass. Compounds of boron with aluminum and nitrogen are almost as hard as diamond and are used to grind and polish metal. Boron is also used in nuclear reactor components, rocket parts, and jet nozzles. Although small amounts are essential for plant growth, the element is toxic in large quantities.
Boron was isolated in June 1808 by the French chemists Joseph Gay-Lussac (1778-1850) and Louis-Jacques Thenard (1777-1857). Nine days later, it was independently isolated by the Englishman Humphry Davy (1778-1827). It is named after borax, its main compound.
Its atomic number is 5, and its atomic mass is 10.81. Its melting point is about 2300° C, and its boiling point is about 2550° C.
Aluminum
Lightweight silver-colored aluminum is the most abundant metallic element in the earth’s crust after oxygen and silicon. Although present in clay, it is most concentrated in bauxite, a mixture of hydrous (water-bearing) oxides and the principal ore of the metal. Pure aluminum is too soft and weak for most purposes, so it is usually combined with up to 15 per cent of various other metals, including copper, zinc, and magnesium—for strength and hardness— and manganese and tin for other desirable qualities. Alloyed with these metals, aluminum acquires some very valuable properties: (1) it weighs only one third as much as steel, so it can be used to produce lighter-weight, more fuel-efficient cars and trucks; (2) the fact that it resists corrosion makes it valuable for outdoor use, such as window frames, rain gutters, lawn furniture, and boats; (3) though it conducts electricity less efficiently than copper, it is so much lighter that it is used in high-voltage power lines; (4) because it conducts heat so well it is used in cookware; and (5) because it is such a qood reflector, it is used in liqhtinq fixtures.
Aluminum was first isolated in crude form in 1825 by the Danish scientist Hans Oersted (1777-1851). Its name is derived from the Latin alumen, meaning alum. Its atomic number is 13, and its atomic mass is 26.9815. Its melting point is 660.37° C, and its boiling point, 2467° C.
Gallium, indium, and thallium
Gallium is a soft, silvery metal that remains liquid over a wider range of temperatures than any other element Its melting point is just under human body temperature, making it the only metal that melts in the hand. Its boiling point is so high that it is used to record temperatures that would vaporize conventional thermometers. Otherwise, its uses are limited mainly to electronic devices such as LEDs (light-emitting diodes) and memory chips for high-speed computers.
Gallium was discovered in 1875 by the French chemist Emile Lecoq de Boisbaudran (1838-1912). He named it after the Latin word (Gallium)ior his homeland. Its atomic number is 31, and its atomic mass is 69.72. Its melting point is 29.78° C, and its boiling point is about 2403° C.
Indium is a soft, lustrous silvery metal too scarce for wide use. It is used to coat the bearings of diesel engines to make them run more smoothly and also in the manufacture of transistors and other electronic devices.
Indium was discovered in 1863 by the German scientists Ferdinand Reich (1799-1882) and H. T. Richter (1824-1898). Its name derives from the Latin indicum, meaning indigo, the color of the element’s dominant spectral lines. Its atomic number is 49, and its atomic mass is 114.82. Its melting point is 156.61° C, and its boiling point, 2080° C.
Thallium is a soft blue-gray metal resembling lead. Its extreme toxicity makes thallium sulfate a common ingredient in rat and ant poison. Other thallium compounds are used in devices that measure infrared radiation.
Thallium was first identified in 1861 by the British scientist William Crookes (1832-1919). Characterized by a bright green line in its spectrum, the element’s name comes from the Greek thallos, meaning green twig. Its atomic number is 81, and its atomic mass is 204.383. Its melting point is 303.5° C, and its boiling point, 1457±10° C.
