The study of the element carbon and its compounds is often described as the study of organic chemistry. Indeed, the amount of knowledge about carbon compounds is now so great that organic chemistry and inorganic chemistry have come to be recognized as important disciplines in their own right. Today the distinction between inorganic and organic chemistry is a somewhat arbitrary one. The term organic chemistry is generally applied to the study of carbon compounds other than metallic carbonates, hydrogencarbonates and the oxides of carbon.
The number of carbon-based compounds is greater than the sum of all other known compounds that do not contain carbon. Several million carbon compounds have been prepared and isolated, so it is convenient to examine this large group of compounds as a separate field of study. The study of organic compounds is also justified because they exhibit great diversity of properties and are used extensively in modern society. Coal, wood, oil, soaps, detergents, antibiotics, rubber, pesticides, wool, alcohols, fuels, carbohydrates, proteins and plastics represent some examples of important organic substances.
The most common isotope of carbon has an atomic number of six and a mass number of twelve. Hence the nucleus of a carbon atom contains six protons and six neutrons. Six electrons are distributed in the space around the nucleus of each carbon atom. In the ground or lowest energy state, a carbon atom has an electron configuration of 2,4.
In organic compounds, carbon atoms almost always from four bonds. This suggests that the four valence electrons, two 2s electrons and two 2p electrons are involved in the bonding. An examination of simple carbon-based molecules like methane (CH4) and carbon tetrachloride (CCl4) indicates that in these compounds the carbon forms four identical single bonds and that the angles between the bonds are 109.5 degrees. It can be predicted from the valence shell electron repulsion (VSEPR) theory that a tetrahedral orientation of the electron pairs is required to minimize the electrostatic repulsion between them
The central role of carbon in organic chemistry depends on the fact that carbon atoms can form chains of virtually unlimited length containing a succession of carbon-carbon bonds. The valance electrons not involved in forming carbon-carbon bonds are used in forming bonds with atoms of other elements such as hydrogen, oxygen and nitrogen. There are a variety of carbon-carbon bonds generally classified under the type of bonding between the two carbon atoms, whether it be a single, double or triple bond.