Isotope Abundances
Individual elements naturally occur in multiple forms called isotopes. Isotopes differ in the number of neutrons within the atom’s nucleus. Rarely these isotopes are unstable and referred to as radioactive isotopes; however, most isotopes are stable. Consider the stable isotopes of the element hydrogen. As diagrammed below, hydrogen (H) atoms most commonly have a single proton in the nucleus and are referred to as 1H. In some cases, H atoms will have an additional neutron within the nucleus and are referred to as 2H.
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The elements hydrogen (H), carbon (C), nitrogen (N), and oxygen (O) are the primary building blocks of organic matter. Thus, they are the elements most commonly analyzed in stable isotope research. Each of the elements has one common isotope form and one or more rare forms. Stable isotope abundances are shown in the table below.
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