The essential difference between organic and inorganic compounds is, quite simply, that organic compounds contain carbon. More specifically, it refers to complex molecules based on carbon’s unique ability to form up to four chemical bonds per atom; certain chemical compounds contain carbon (carbonates, cyanides, and oxides, like carbon dioxide) but are still classified as inorganic, and some scientists argue that organic should be redefined to include only those which contain BOTH carbon and hydrogen. Because organic compounds can be extremely long and complex, and are especially important as the building blocks of life, they are one of the most important parts of the study of chemistry generally; the study of organic compounds is referred to as organic chemistry.
AN OLD TERM
Although our current understanding of chemical compounds is at most a few centuries old, the classification of “organic” material is much older. It stems from the alchemic theory of vitalism, which held that the compounds necessary to life (the “organic” compounds) were all made up of the four classical elements, Earth, Water, Air and Fire. However, even after the vitalism theory was convincingly disproved by early chemists, the theory that the chemical building blocks of life were somehow separate from the inorganic materials from the non-living world, and that one could not be used to create the other, survived until the 1820s. During that decade, Friedrich Wohler was able to produce two organic chemicals, oxalic acid and urea (the major component of urine) through the right mixes of “inorganic” materials.
With the vitalism theory that gave rise to the term “organic” now obsolete, the classification is arguably obsolete as well. However, it still remains in chemistry, not as a formal division between naturally different types of chemicals but rather a useful distinction between carbon-based compounds and other chemical compounds. As a result, there are now many “organic” compounds which are actually not “organic” in the sense that they come from living plants or animals. Plastic, for example, is a synthetic compound which we produce artificially rather than remove from living beings. Some organic compounds, like benzene and gasoline, are even highly toxic to life.
EXAMPLES OF COMPOUNDS
Most inorganic compounds are comparatively simple. These include elements which have joined together through ionic bonds to form basic chemicals such as common table salt (one sodium and one chlorium atom, or NaCl), and water (two hydrogen and one oxygen atoms, or H2O). Certain simple carbon compounds are also considered inorganic: for example, carbon dioxide (one carbon and two oxygen atoms, or CO2) is an inorganic compound.
Organic compounds, by contrast, vary much more widely in terms of what they contain as well as how large they are. In all cases, carbon compounds take advantage of carbon’s unique ability to form up to four bonds per atom to string together unusually complex chains of atoms. The simplest of these can be quite short, such as methane (one carbon atom and four hydrogen atoms, or CH4) and ethanol, which we usually refer to by its more generic name, alcohol (one oxygen, two carbon, and six hydrogen atoms).
However, organic compounds can also come in extremely long and complex forms: human DNA, for example, is an organic compound consisting of many thousands of atoms arranged in a very specific order. In these complex organic compounds, order actually matters: in some cases, the same group of atoms could be combined in a different order, and could in that way become a different compound with different properties.