The six elements of group 2A of the periodic table are called alkaline earth metals because their oxides have long been known as alkaline earths, compounds that form basic alkaline solutions that neutralize acids. In order of in-, creasing chemical reactivity, the six are: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Although they are less reactive than the alkali metals, they all react with water and have similar properties. No member of this group is ever found in pure form in nature, so they must be separated from the mineral compounds in which they occur.
Beryllium and magnesium
Beryllium is a rare, gray metal similar in appearance to aluminum and magnesium, but lighter and stronger and with a much higher melting point. It is used as a “moderator’ in nuclear reactors, where it slows fast neutrons, making it possible to control the rate of fission. It is highly poisonous and occurs sparingly, primarily in the mineral beryl, so its uses are limited to high-tech metallurgical applications. Small amounts are added to copper and other metals to create strong, corrosion-resistant, lightweight alloys. In solid-rocket propellant, it increases the thrust of the rocket, and its high melting point of 1287°C makes it useful in the nose cones for missiles.
Calcium, strontium, and barium
Calcium, a soft, silvery-white metal, is the fifth most abundant element, making up about 3.5 per cent of the earth’s crust. The commonest and cheapest of the alkaline earth metals, its compounds occur naturally in many forms, including chalk, marble, gypsum, limestone, seashells, and the mineral calcite. Huge quantities of these compounds are used in building and construction. Heating limestone produces quicklime, which is treated with water to make slaked lime, used in mortar and brickwork. Hydroxide and sulfate compounds are the basis of cement and plaster, respectively, and are also used in tanning leather, refining petroleum, and making fertilizer, paint, and many other products. Calcium is essential to life necessary for the growth and maintenance of teeth ana bones. It helps control muscle action and blood clotting, as well as transmission of impulses by neurons of the nervous system. Calcium deficiency causes rickets, but an oversupply of calcium causes hardening of joints and formation of kidney stones.
Radium
Radium, a white metal that tarnishes in the air, is highly radioactive, as are its compounds, found mainly in uranium and thorium ores. Radioactive decay of uranium produces radium isotopes, which are also unstable and decay eventually to lead. Once used in treating cancer and making fluorescent paint, radium has been replaced by cheaper, safer substitutes. The radiation it emits destroys body tissue and can cause bone cancer.
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