Understanding the Difference Between Carbon-12 and Carbon-14

Carbon-12 and carbon-14 are two isotopes of the element carbon. The difference between carbon-12 and carbon-14 is the number of neutrons in each atom. The number given after the atom name (carbon) indicates the number of protons plus neutrons in an atom or ion. Atoms of both isotopes of carbon contain 6 protons. Atoms of carbon-12 have 6 neutrons, while atoms of carbon-14 contain 8 neutrons. A neutral atom would have the same number of protons and electrons, so a neutral atom of carbon-12 or carbon-14 would have 6 electrons.

Although neutrons do not carry an electrical charge, they have a mass comparable to that of protons, so different isotopes have different atomic weight. Carbon-12 is lighter than carbon-14.

Because of the different number of neutrons, carbon-12 and carbon-14 differ with respect to radioactivity. Carbon-12 is a stable isotope. Carbon-14, on the other hand, undergoes radioactive decay:

¹⁴₆C → ¹⁴₇N + ⁰_-1e (half-life is 5720 years)

The other common isotope of carbon is carbon-13. Carbon-13 has 6 protons, just like other carbon isotopes, but it has 7 neutrons. It is not radioactive.

Although 15 isotopes of carbon are known, the natural form of the element consists of a mixture of only three of them: carbon-12, carbon-13, and carbon-14. Most of the atoms are carbon-12.

Measuring the difference in the ratio between carbon-12 and carbon-14 is useful for dating the age of organic matter since a living organism is exchanging carbon and maintaining a certain ratio of isotopes. In a diseased organism, there is no exchange of carbon, but the carbon-14 that is present undergoes radioactive decay, so over time, the isotope ratio becomes more and more different.