Inorganic Compound

inorganic compound, any substance in which two or more chemical elements (usually other than carbon) are combined, nearly always in definite proportions. Compounds of carbon are classified as organic when carbon is bound to hydrogen. Carbon compounds such as carbides (e.g., silicon carbide [SiC₂]), some carbonates (e.g., calcium carbonate [CaCO₃]), some cyanides (e.g., sodium cyanide [NaCN]), graphite, carbon dioxide, and carbon monoxide are classified as inorganic.

Read about the differences between inorganic compounds and organic compounds in the article chemical compound.

structure of the three-centre, two-electron bond in a B―H―B fragment of a diborane molecule

Inorganic compounds include compounds that are made up of two or more elements other than carbon, as well as certain carbon-containing compounds that lack carbon-carbon bonds, such as cyanides and carbonates. Inorganic compounds are most often classified in terms of the elements or groups of elements that they contain. Oxides, for example, can be either ionic or molecular. Ionic oxides contain O²⁻ (oxide) ions and metal cations, whereas molecular oxides contain molecules in which oxygen (O) is covalently bonded to other nonmetals such as sulfur (S) or nitrogen (N). When ionic oxides are dissolved in water, the O²⁻ ions react with water molecules to form hydroxide ions (OH⁻), and a basic solution results. Molecular oxides react with water to produce oxyacids, such as sulfuric acid (H₂SO₄) and nitric acid (HNO₃). In addition, inorganic compounds include hydrides (containing hydrogen atoms or H⁻ ions), nitrides (containing N³⁻ ions), phosphides (containing P³⁻ ions), and sulfides (containing S²⁻ ions).

Transition metals form a great variety of inorganic compounds. The most important of these are coordination compounds in which the metal atom or ion is surrounded by two to six ligands. Ligands are ions or neutral molecules with electron pairs that they can donate to the metal atom to form a coordinate-covalent bond.

The resulting covalent bond is given a special name because one entity (the ligand) furnishes both of the electrons that are subsequently shared in the bond. An example of a coordination compound is [Co(NH₃)₆]Cl₃, which contains the Co(NH₃)₆³⁺ ion, a cobalt ion (Co³⁺) with six ammonia molecules (NH₃) attached to it, acting as ligands.

In the early days of the science of chemistry, there was no systematic approach to naming compounds. Chemists coined names such as sugar of lead, quicklime, milk of magnesia, Epsom salts, and laughing gas to describe familiar compounds. Such names are called common or trivial names. As chemistry advanced, it became evident that, if common names were used for all known compounds, which number in the millions, great confusion would result. It clearly would be impossible to memorize trivial names for such a large number of compounds. Therefore a systematic nomenclature (naming process) has been developed. There are, however, certain familiar compounds that are always referred to by their common names. The systematic names for H₂O and NH₃, for example, are never used; these vital compounds are known only as water and ammonia, respectively.

The simplest chemical compounds are binary compounds—those consisting of two elements. Different rules apply for the nomenclature of binary ionic compounds and binary molecular (covalent) compounds, and so they will be considered separately.