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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 H2O, 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

com·pound1 • n. / ˈkämˌpound/ a thing that is composed of two or more separate elements; a mixture. ∎  (also chemical compound) a substance formed from two or more elements chemically united in fixed proportions: a compound of hydrogen and oxygen. ∎  a word made up of two or more existing words, such as steamship. • adj. / ˈkämˌpound; kämˈpound; kəmˈpound/ made up or consisting of several parts or elements, in particular: ∎  (of a word) made up of two or more existing words or elements: a compound noun. ∎  (of interest) payable on both capital and the accumulated interest: compound interest.Compare with simple. ∎  Biol. (esp. of a leaf, flower, or eye) consisting of two or more simple parts or individuals in combination. • v. / kəmˈpound; kämˈpound; ˈkämˌpound/ [tr.] 1. (often be compounded) make up (a composite whole); constitute: a dialect compounded of Spanish and Dutch. ∎  mix or combine (ingredients or constituents). ∎  calculate (interest) on previously accumulated interest. ∎  (of a sum of money invested) increase by compound interest: let your money compound for five years. 2. make (something bad) worse; intensify the negative aspects of: I compounded the problem by trying to make wrong things right. 3. Law forbear from prosecuting (a felony) in exchange for money or other consideration. ∎  settle (a debt or other matter) in this way. DERIVATIVES: com·pound·a·ble / kəmˈpoundəbəl; käm-/ adj. ORIGIN: late Middle English compoune (verb), from Old French compoun-, present tense stem of compondre, from Latin componere ‘put together.’ The final -d was added in the 16th cent. on the pattern of expound and propound. com·pound2 / ˈkämˌpound/ • n. an area enclosed by a fence, in particular: ∎  an open area in which a factory or large house stands. ∎  an open area in a prison, prison camp, or work camp.

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compound

compound Substance formed by chemical combination of two or more elements that cannot be separated by physical means. Compounds are produced by the rearrangement of valency electrons (outer electrons of an atom) seeking more stable configurations. They usually have properties different from their constituent elements. Ionic compounds have ionic bonds – they are collections of oppositely charged ions. They have high melting and boiling points, due to the electrostatic forces of attraction holding their crystal lattice together. Covalent bonds occur where non-metal atoms share electrons. Such compounds can be classified as simple molecular structures, such as carbon dioxide, with low melting and boiling points; or giant molecular structures, such as graphite and diamond. Their properties depend on the arrangement of the atoms in the macromolecule. See also molecule; valence

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compound

compound 2 put together, combine, compose XIV; trans. and intr. settle differences, etc. XV. ME. compoune — OF. compo(u)n-, pres. stem of compondre :- L. compōnere put or bring together, arrange, devise; see COM-, POSITION. The orig. ME. form was superseded by the present form in XVI.

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compound

compound 3 in the East, enclosure within which a (European) residence or factory stands. XVII. — Pg. campon or Du. kampoeng — Malay kampong enclosure, fenced-in space, quarter occupied by a particular nationality.

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compound

compound 1 compounded, composite. XIV. pp. of compoune; see next.
Also sb. compound word XVI; compound substance XVII.

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Compound

Compound

a union; a chemical bonding of elementsWilkes.

Example: compound of two liquids, 1710.

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compound

compound Applied to flowers or leaves that have two or more parts. Compare SIMPLE.

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compound

compoundabound, aground, around, astound, bound, compound, confound, dumbfound, expound, found, ground, hound, impound, interwound, mound, pound, profound, propound, redound, round, sound, stoneground, surround, theatre-in-the-round (US theater-in-the-round), underground, wound •spellbound • westbound • casebound •eastbound • windbound • hidebound •fogbound • stormbound •northbound • housebound •outbound • southbound • snowbound •weatherbound • earthbound •hellhound • greyhound • foxhound •newshound • wolfhound •bloodhound • background •battleground • campground •fairground • playground •whip-round • foreground •showground • merry-go-round •runaround • turnaround • ultrasound •pre-owned, unowned •unchaperoned • poind • untuned •Lund

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