Water molecules are composed of two hydrogen atoms and one oxygen atom (H2O). If the hydrogen atoms of a water molecule are replaced by deuterium atoms, the result is heavy water (D2O). Deuterium differs from hydrogen by having one neutron in the nucleus of the atom. There is approx. one part in 5000 D2O in normal water and it can be concentrated by electrolysis. Heavy water has a higher boiling point (101.4 °C) and melts at 3.6 °C. Heavy water is 20/18=1.11 times heavier than ordinary water.
Generalic, Eni. "Heavy water." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
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