An inorganic compound is a chemical substance that does not originate from life. This term historically described materials found in the mineral or non-living world, such as rocks, metals, and water. The modern scientific distinction is structural, requiring separation of its precise chemical definition from its broader, everyday usage.
The Core Definition in Chemistry
An inorganic compound is generally defined as one that lacks carbon-hydrogen (C-H) bonds. This category encompasses the vast majority of all chemical compounds, including salts, metals, mineral acids, and noble gases. Examples of common inorganic compounds include water (\(\text{H}_2\text{O}\)), table salt (sodium chloride, \(\text{NaCl}\)), and rust (iron oxide, \(\text{Fe}_2\text{O}_3\)).
Lacking C-H bonds means inorganic compounds often have different properties than their organic counterparts, such as higher melting points and greater solubility in water. They are typically composed of metal and non-metal elements, frequently forming ionic bonds rather than the covalent bonds common in organic molecules. However, the definition is not absolute, as several simple carbon-containing substances are classified as inorganic. Carbon oxides, such as carbon dioxide (\(\text{CO}_2\)) and carbon monoxide (\(\text{CO}\)), along with carbonates like calcium carbonate (\(\text{CaCO}_3\)), are notable exceptions.
How Inorganic Differs from Organic
The primary difference between inorganic and organic chemistry is the presence and bonding of carbon. Organic compounds are defined by carbon atoms bonded to hydrogen, forming the basis for the complex molecules of life. Inorganic compounds, by contrast, cover all other chemical substances, including compounds of the remaining elements on the periodic table.
This distinction arose historically from the 19th-century doctrine of vitalism. This doctrine held that a “vital force” was necessary to create organic compounds, meaning they could only be produced by living organisms. This theory was discredited in 1828 when chemist Friedrich Wöhler synthesized urea, an organic compound, from the inorganic salt ammonium cyanate.
The two fields remain distinct because of fundamental differences in molecular structure and reaction types. Organic molecules are generally larger and more complex, featuring covalent bonds that form the backbones of biological polymers. Inorganic compounds tend to be smaller, simpler molecules or extended solids, frequently participating in reactions involving ionic interactions and coordination chemistry.
Practical Contexts and Common Misunderstandings
The term “inorganic” is used in various fields outside of strict chemical classification, which can lead to confusion. In geology, inorganic materials are the basis of the planet, referring to all minerals, rocks, and substances. The vast majority of the Earth’s crust, including silicates, metal ores, and salts, is composed of inorganic compounds.
A common misunderstanding is in nutrition, where dietary minerals like calcium, iron, and sodium are correctly labeled as inorganic nutrients. These elements are chemical substances that do not contain C-H bonds and are obtained from the earth or water, not synthesized by the body. The chemical definition of inorganic has no relation to the consumer term “organic food,” which refers to agricultural practices that prohibit synthetic pesticides and fertilizers.
Another frequent point of confusion is equating “inorganic” with “synthetic” or “artificial.” This is inaccurate, as many naturally occurring substances, such as table salt and nearly all minerals, are inorganic. While many inorganic compounds are manufactured in a lab, they still adhere to the chemical definition of lacking carbon-hydrogen bonds.