The terms “organic” and “inorganic” mean something different in chemistry than when you’re talking about food and produce. Organic and inorganic compounds form the basis for organic chemistry and inorganic chemistry. Organic chemists study organic molecules, their synthesis, and the reactions between them. Inorganic chemists study all other types of substances, including salts, metals, and minerals.
The main difference between the two classes of substances is that organic compounds always contain the element carbon, while most inorganic compounds lack this element. Because there are carbon-containing inorganic compounds, the presence of carbon is not sufficient to classify a compound as organic! With very few exceptions, organic compounds contain carbon atoms bonded to hydrogen atoms to form the C-H bonds. Many organic compounds also contain oxygen atoms.
Examples of Organic Compounds
Compounds made within living organisms are organic molecules. The main classes of organic compounds are carbohydrates, fats, proteins, and nucleic acids.
Examples of organic substances include:
- Sucrose (table sugar), C12H22O11
- Methane, CH4
- Benzene, C6H6
- Ethanol (grain alcohol), C2H6O
- Hair and fingernails (keratin protein)
Organic Compounds Lacking C-H Bonds
There are a few organic compounds containing carbon, but no C-H bond. Examples include:
- Carbon tetrachloride, CCl4
- Urea, CO(NH2)2
Examples of Inorganic Compounds
Inorganic substances include all pure elements, salts, many acids and bases, metals and alloys, and minerals. Compounds in which a non-carbon atom forms a chemical bond with hydrogen are inorganic.
Examples of inorganic compounds include:
- Sodium chloride (table salt) (NaCl)
- Glass and quartz (SiO2)
- Hydrochloric acid (HCl)
- Sulfuric acid (H2SO4)
Inorganic Molecules Containing Carbon
A few inorganic compounds contain carbon. These include the oxides, carbides, some carbonates, and some cyanides, Examples include:
- Carbon dioxide (CO2)
- Cyanides (C-N bond)
- Carbides (e.g., boron carbide, B4C)
- Carbon disulfide (CS2)
- Phosgene (COCl2)
Note the hydrogen cyanide, HCN, contains both carbon and hydrogen. It is usually considered to be an inorganic compound because of the bond between carbon and nitrogen. Diamond, graphite, and graphene consist of pure carbon. They are inorganic.
Neither Organic nor Inorganic
Pure elements are not compounds, so they are neither organic nor inorganic compounds:
- Argon (Ar)
- Silver (Ag)
- Sulfur (S)
- Carbon (C)
Not All Organics Come From Life
Most organic compounds are made within living organisms, but the molecules may form via other processes. For example, organic compounds found on Mars or within a nebula aren’t necessarily signs of extraterrestrial life. Solar radiation can supply the energy needed to convert inorganic compounds into organics.