What counts as organic?
An organic compound contains carbon, almost always bonded to hydrogen. Methane, ethanol, glucose, proteins, plastics and most medicines are organic.
A few carbon compounds are treated as inorganic by convention, because they behave like salts or simple minerals: carbon monoxide (CO), carbon dioxide (CO₂), carbonates (such as CaCO₃), hydrogencarbonates, cyanide salts (such as KCN) and carbides. Diamond and graphite are pure carbon and are also usually counted as inorganic.
Side by side
| Organic compounds | Inorganic compounds | |
|---|---|---|
| Based on | Carbon chains and rings, with H, O, N, halogens, S | Any element; metals, salts, minerals |
| Typical bonding | Covalent | Often ionic; also covalent and metallic |
| Melting points | Usually low (many are liquids or gases) | Often high (ionic lattices) |
| In water | Often insoluble unless they have polar groups (–OH, –COOH, –NH₂) | Many salts dissolve and conduct |
| Burning | Most burn, giving CO₂ and H₂O | Most don't burn |
| Reactions | Usually slower; bonds break at a functional group | Often fast, between ions |
| Isomers | Very common | Less common (some complexes) |
| Number known | Many millions | Far fewer |
Why carbon is special
Carbon forms four strong covalent bonds and bonds to itself in long chains and rings (catenation). It forms single, double and triple bonds, and the same atoms can be joined in different ways (isomerism). That's why there are so many organic compounds, and why organic chemistry is a subject of its own.
A bit of history
Chemists once thought organic compounds could only be made by living things ("vitalism"). In 1828 Friedrich Wöhler made urea, a compound found in urine, by heating ammonium cyanate, an inorganic salt. Today "organic" just means "carbon-based", and has nothing to do with whether something came from a living thing.
Quick answers
Is CO₂ organic or inorganic?
Carbon dioxide is classed as inorganic, even though it contains carbon. So are carbon monoxide, carbonates, hydrogencarbonates and cyanide salts.
What is the main difference between organic and inorganic chemistry?
Organic chemistry studies carbon compounds, mostly with C–H and C–C bonds. Inorganic chemistry studies all the other elements and compounds, including metals, salts and minerals.
Is water organic?
No. Water contains no carbon, so it is inorganic.
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