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A chemical compound is termed inorganic if it fulfills one or more of the following criteria:
- There is an absence of carbon in its composition
- It is of a non-biologic origin
- It cannot be found or incorporated into a living organism
There is no clear or universally agreed-upon distinction between organic and inorganic compounds. Organic chemists traditionally and generally refer to any molecule containing carbon as an organic compound and by default this means that inorganic chemistry deals with molecules lacking carbon. As many minerals are of biological origin, biologists may distinguish organic from inorganic compounds in a different way that does not hinge on the presence of a carbon atom. Pools of organic matter, for example, that have been metabolically incorporated into living tissues persist in decomposing tissues, but as molecules become oxidized into the open environment, such as atmospheric CO2, this creates a separate pool of inorganic compounds. The International Union of Pure and Applied Chemistry, an agency widely recognized for defining chemical terms, does not offer definitions of inorganic or organic compounds. Hence, the definition for an inorganic versus an organic compound in a multidisciplinary context spans the division between organic life living (or animate) and inorganic non-living (or inanimate) matter. In broader speech, the term commonly referred to compounds synthesised by purely geological systems, in contrast to those with a biological component in their origin.
The Wöhler synthesis is the conversion of ammonium cyanate into urea. This chemical reaction was discovered in 1828 by Friedrich Wöhler and is considered the starting point of modern organic chemistry.
The Wöhler synthesis is of great historical significance because for the first time an organic compound was produced from inorganic reactants. This finding went against the mainstream theory of that time called vitalism, which stated that organic matter possessed a special force or vital force inherent to all things living. For this reason a sharp boundary existed between organic and inorganic compounds. Urea was discovered in 1799 and could until 1828 only be obtained from biological sources such as urine. Wöhler reported to his mentor Berzelius:
"I cannot, so to say, hold my chemical water and must tell you that I can make urea without thereby needing to have kidneys, or anyhow, an animal, be it human or dog".
Inorganic compounds can be defined as any compound that is not organic compound. Some simple compounds which contain carbon are usually considered inorganic. These include carbon monoxide, carbon dioxide, carbonates, cyanides, cyanates, carbides, and thiocyanates. Many of these are normal parts of mostly organic systems, including organisms, which means that describing a chemical as inorganic does not obligately mean that it does not occur within living things. In contrast, methane and formic acid are generally considered to be simple examples of organic compounds, although the Inorganic Crystal Structure Database (ICSD), in its definition of "inorganic" carbon compounds, states that such compounds may contain either C-H or C-C bonds, but not both.
A large class of compounds discussed in inorganic chemistry textbooks are coordination compounds. Examples range from substances that are strictly inorganic, such as [Co(NH3)6]Cl3, to organometallic compounds, such as Fe(C5H5)2, and extending to bioinorganic compounds, such as the hydrogenase enzymes.
Minerals are mainly oxides and sulfides, which are strictly inorganic, although they may be of biological origin. In fact, most of the Earth is inorganic. Although the components of Earth's crust are well-elucidated, the processes of mineralization and the composition of the deep mantle remain active areas of investigation, which are covered mainly in geology-oriented venues.
- Major textbooks on inorganic chemistry, however, decline to define inorganic compounds: Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Francisco, 2001. ISBN 0-12-352651-5; Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9., Cotton, F. Albert; Wilkinson, Geoffrey (1988), Advanced Inorganic Chemistry (5th ed.), New York: Wiley-Interscience, ISBN 0-471-84997-9
- ., Arnoldischen Buchhandlung, Dresden and Leipzig, 1827. ISBN 1-148-99953-1. Brief English commentary in English can be found in Bent Soren Jorgensen "More on Berzelius and the vital force" J. Chem. Educ., 1965, vol. 42, p 394. doi:10.1021/ed042p394
- "organic compound – chemical compound". Encyclopædia Britannica. Archived from the original on 2013-11-06.
- "Archived copy". Archived from the original on 2015-03-17. Retrieved 2015-03-23.
- "ICSD". fiz-karlsruhe.de. Archived from the original on 2014-03-22.
- "Archived copy" (PDF). Archived (PDF) from the original on 2017-08-30. Retrieved 2017-01-13.
- Newman, D. K.; Banfield, J. F. (2002). "Geomicrobiology: How Molecular-Scale Interactions Underpin Biogeochemical Systems". Science. 296 (5570): 1071–1077. PMID 12004119. doi:10.1126/science.1010716. Archived from the original on 2013-10-17.
- Dan Berger, Bluffton College, analysis of varying inappropriate definitions of the inorganic-organic distinction: Otherwise consistent linked material differing from current article in downplaying the carbon present vs carbon absent distinctive: