Carbon isotopes

Generally speaking, an element’s defining characteristic is based on the number of protons an atom has. An atom with eight protons makes oxygen. An atom with nine protons makes fluorine, a poisonous gas. But an atom can have a varying number of neutrons without radically changing its properties.

These atomic variations of the same element are called isotopes. They are either stable or radioactive. C12 and C13 are stable. C14, used in carbon-14 dating, is radioactive and decays at a rate that allows scientists to determine the age of organic material.