Compound, Chemical

a complex substance consisting of chemically bound atoms of two or more different elements. Certain simple substances can be considered chemical compounds if their molecules consist of atoms linked by a covalent bond, for example, nitrogen (N₂) and oxygen (O₂). The composition of a chemical compound is expressed through a chemical formula, and the structure is often represented by a structural formula. In the vast majority of cases, chemical compounds obey the law of definite proportions and the law of multiple proportions. However, many compounds of variable composition are known.

Chemical compounds are obtained through chemical reactions. The formation of a chemical compound is accompanied by either liberation of energy (exothermic reaction) or absorption of energy (endothermic reaction). The physical and chemical properties of chemical compounds differ from the properties of the substances from which the compounds are obtained. Chemical compounds are characterized by definite values for density, melting point, boiling point, and other constants. Compounds possessing the same composition but different structures have different properties. Chemical compounds are divided into inorganic and organic compounds. More than 100,000 inorganic compounds and more than 3 million organic compounds are known.