Classes of chemical compounds are molecules grouped by similar characteristics. The first sign of separation of the substance - this is by the number of atoms. Simple substances consist of an atom of one element, complex substances consist of atoms different elements. Examples of a simple substance can be copper (Cu), oxygen (O), ozone (O3) and others. Simple substances are divided into metals and nonmetals. Metallic properties are the ability to release electrons from an external level. Ability to accept electrons it is called a non-metallic property of a substance. The division of simple substances is reflected in the periodic table, different classes of simple substances are highlighted in different colors. In 2005 , IUPAC was established separation of simple substances. For a description of simple things, see the article Simple substances.
Complex substances are divided into inorganic, organic and organometallic, inorganic and organic substances are studied separately by inorganic and organic chemistry, respectively. Division into organic and inorganic initially, it was due to the fact that some elements were only in living nature. In 1828 Friedrich Weller synthesized urea from an inorganic compound, after which organic chemistry was separated by the chemistry of compounds with carbon, with the exception of carbides, carbonates, cyanides, carbon oxides and carbonic acid.
The classification of complex compounds can be found in the section inorganic chemistry and organic chemistry.
