compound
compound, in chemistry, a substance composed of
atoms of two or more
elements in chemical combination, occurring in a fixed, definite proportion and arranged in a fixed, definite structure. A compound is often represented by its chemical
formula. The formula for water is H
2O, and for sodium chloride, NaCl. The
formula weight of a compound can be determined from its formula. The
molecular weight of a molecular compound can be determined from its molecular formula. Two or more distinct compounds that have the same molecular formula but different properties are called
isomers.
Formation and Decomposition of Compounds
Compounds are formed from simpler substances by chemical reaction. Some compounds can be formed directly from their constituent elements, e.g., water from hydrogen and oxygen: 2H2 + O2 → 2H2O. Other compounds are formed by reaction of an element with another compound; e.g., sodium hydroxide (NaOH) is formed (and hydrogen gas released) by the reaction of sodium metal with water: 2Na + 2H2O → 2NaOH + H2↑. Compounds are also made by reaction of other compounds; e.g., sodium hydroxide reacts with hydrogen chloride (HCl) to form sodium chloride and water: HCl + NaOH → NaCl + H2O. Complex molecules such as proteins are formed by a series of reactions involving elements and simple compounds.
Compounds can be decomposed by chemical means into elements or simpler compounds. Water is broken down into hydrogen and oxygen by electrolysis. Candle wax, a mixture of hydrocarbons, is changed in the candle flame by combustion (with oxygen) to a mixture of the simpler compounds carbon dioxide (CO2) and water. Life is based on numerous reactions in which energy is stored and released as compounds are produced and decomposed.
Properties of Compounds
A compound has unique properties that are distinct from the properties of its elemental constituents. One familiar chemical compound is water, a liquid that is nonflammable and does not support combustion. It is composed of two elements: hydrogen, an extremely flammable gas, and oxygen, a gas that supports combustion. A compound differs from a mixture in that the components of a mixture retain their own properties and may be present in many different proportions. The components of a mixture are not chemically combined; they can be separated by physical means. A mixture of hydrogen and oxygen gases is still a gas and can be separated by physical methods. If the mixture is ignited, however, the two gases undergo a rapid chemical combination to form water. Although the hydrogen and oxygen can occur in any proportion in a mixture of gases, they are always combined in the exact proportion of two atoms of hydrogen to one atom of oxygen when combined in the compound water. Another familiar compound is sodium chloride (common salt). It is composed of the silvery metal sodium and the greenish poisonous gas chlorine combined in the proportion of one atom of sodium to one atom of chlorine.
Molecular and Ionic Compounds
Water is a molecular compound; it is made up of electrically neutral
molecules, each containing a fixed number of atoms. Sodium chloride is an ionic compound; it is made up of electrically charged
ions that are present in fixed proportions and are arranged in a regular, geometric pattern (called crystalline structure) but are not grouped into molecules. The atoms in a compound are held together by chemical bonding (see
chemical bond).
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compound
[′käm‚pau̇nd] (chemistry)
A substance whose molecules consist of unlike atoms and whose constituents cannot be separated by physical means. Also known as chemical compound.
(petroleum engineering)
A power transmission mechanism that transfers power from the engines to the pump, drawworks, and other machinery on a drilling rig.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
compound
11. a substance that contains atoms of two or more chemical elements held together by chemical bonds
2. Musica. denoting a time in which the number of beats per bar is a multiple of three
b. (of an interval) greater than an octave
4. (of a steam engine, turbine, etc.) having multiple stages in which the steam or working fluid from one stage is used in a subsequent stage
5. (of a piston engine) having a turbocharger powered by a turbine in the exhaust stream
compound
2 (formerly in India, China, etc.) the enclosure in which a European's house or factory stood
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005