A chemical compound is a pure substance consisting of atoms of two or more chemical elements, whereby - in contrast to mixtures - the types of atoms are in a fixed ratio to each other. The numerical ratio of the atoms to each other is determined by chemical bonds between the atoms, and the ratio can be represented in a sum formula. However, a molecular formula is often ambiguous, since isomeric compounds have the same molecular formula but are different compounds. Each chemical compound is characterized by its unique chemical structure.
Among the more than 100 million chemical compounds known (as of June 2015), a distinction is made between roughly ionic or salt-like compounds and complex, metallic and molecular compounds. The subdivision inorganic or organic is also fundamental, whereby “organic” - with a few exceptions - refers to the carbon compounds. There are significantly more organic compounds than inorganic compounds. The more than 6 million organic compounds are contrasted by less than 100,000 compounds of an inorganic nature.
Basically, there are four types of chemical compounds with regard to the type of bond between the elements involved:
- Molecular compounds (usually consisting of a non-metallic element and one or more other non-metals)
- Ionic compounds (usually consisting of a metal and one or more non-metals)
- Metallic compounds (of metals)
- Complex compounds (of metal cations and ions or molecules)
A more precise distinction between compounds and their assignment to one of these four types can be made with the help of the electronegativity difference of the elements involved in the bond. There are also transitional forms between the four ideal types mentioned above.