Isotopic Composition of Water Molecules

The definitions of elements and isotopes were presented in sections 5.1 and 5.2. Elements are defined by the number of protons in the nucleus of their atoms. Hydrogen has one proton and oxygen has eight protons. Isotopes are defined as variations of a given element, differing from each other by the number of neutrons. As presented in section 5.2, the hydrogen isotopes are 

Tritium is radioactive and will be discussed in Chapter 10 common hydrogen and deuterium are stable. Oxygen has the following isotopes  

170—heavy (very rare) oxygen 8 protons + 9 neutrons 

Water is composed of hydrogen and oxygen, so it occurs with different isotopic combinations in its molecules. Most common and of interest to hydrochemists are 2 lfiO (common), HD ieO (rare), and lsO (rare). The water molecules may be divided into light molecules ( ieO) and heavy water molecules ( IID ieO and H2 1sO). 

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