Symbol, Chemical

views updated

Symbol, Chemical

Chemical symbols are shorthand abbreviations of the names of the 111 discovered, confirmed and, officially named chemical elements (as of October 2006). Each element has its own unique symbol. Since science is an international enterprise, chemical symbols are determined by international agreement.

The use of symbols for the chemical elements existed long before a systematic method was developed. The alchemists associated the symbols of the planets not only with the days of the week, but also with the seven metals known at the time: gold, silver, iron, mercury, tin, copper, and lead. For example, in Etienne Geoffroys (16721731) table of chemical affinities, published in 1718, the astrological symbol for Mars is used to indicate iron; while the symbol for the sun, a circle with a dot in the center, is used for gold. The symbolism is not accidental: the importance of the sun in astrology clearly parallels the exalted position of gold in alchemy. Geometrical figures, such as triangles, and circled letters were also used, such as N for nickel and M for manganese. By the beginning of the nineteenth century, there were about 26 known elements, but by the beginning of the twentieth century, there were more than 81.As more elements were discovered, the need for symbolic representations for these elements became more evident.

During the first half of the nineteenth century, Swedish chemist Jöns Jacob Berzelius (17791848), systematically assigned letters as symbols for the elements. Chemists everywhere soon accepted this method. Today, the International Union of Pure and Applied Chemistry (IUPAC) is the organization that makes the final decision on the names and symbols of the chemical elements.

Chemical symbols are composed of one or two letters. The first letter is always capitalized and the second, if there is one, is always lowercase. Often these are the first two letters of the elements name but this is not always possible, because it would sometimes cause duplication. For example, the symbol C represents carbon, Ca represents calcium, Cd represents cadium, and Cf represents californium.

Most of the elements have symbols derived from their English name, but a few symbols stem from other languages. Notable among these are ten common elements whose names and symbols are derived from Latin. These are: antimony, Sb, from stibium; copper, Cu, from cuprum; gold, Au, from aurum; iron, Fe, from ferrum; potassium, K, from kalium; lead, Pb, from plumbum; mercury, Hg, from hydrargyrum; silver, Ag, from argentum; sodium, Na, from natrium; and tin, Sn, from stannum.

Chemical symbols are used by chemists everywhere in writing chemical formulas, in which the symbols represent the atoms of the elements present in a compound.

Some strange-looking element names with even stranger-looking three-letter symbols have been in general use recently for the heaviest chemical elements. Because they may still be seen in periodic tables published between 1980 and 1994, it is important to know what they mean. For example the element of atomic number 104 was referred to as unnilquadium, with the symbol Unq, and element 108 was referred to as unniloctium, with the symbol Uno. These names and symbols are based entirely on the atomic numbers themselves: un means 1, nil means 0, and quad means 4; therefore unnil-quad means 104. These names and symbols were recommended by the International Union of Pure and Applied Chemistry to be used temporarily, until certain disputes about who discovered these elements could be resolved.

The discoverers of a new element have historically been given the right to suggest a name. But three groups of nuclear chemists all claim to have been the first to discover some of the transuranium elements: an American group at the Lawrence Berkeley Laboratory in California, a Russian group at the Joint Institute for Nuclear Research in Dubna, and a German group at the Gesellschaft für Schwerionenforschung in Darmstadt. In 1994, the International Union of Pure and Applied Chemistry attempted to settle the issues by recommending official names and symbols for elements 101 through 109. In October 2006, the names (and their symbols and numbers) of the elements from 101 to 111 are: Mendelevium (Md, 101), Nobelium (No, 102), Lawrencium (Lr, 103), Rutherfordium (Rf, 104), Dubnium (Db, 105), Seaborgium (Sg, 106), Bohrium (Bh, 107), Hassium (Hs, 108), Meitnerium (Mt, 109), Darmstadtium (Ds, 110), and Roentgenium (Rg, 111). The temporarily named chemical elements 112 to 118 are: Uub (112), Uut (113), Uuq (114), Uup (115), Uuh (116), Uus (117), and Uuo (118).

See also Element, chemical; Periodic table.