Editing Deuterium (section)

=== Physical properties ===

Compared to hydrogen in its natural composition on Earth, pure deuterium ({{sup|2}}H{{sub|2}}) has a higher [[melting point]] (18.72&nbsp;K vs. 13.99&nbsp;K), a higher [[boiling point]] (23.64 vs. 20.27&nbsp;K), a higher [[Critical point (thermodynamics)|critical temperature]] (38.3 vs. 32.94&nbsp;K) and a higher critical pressure (1.6496 vs. 1.2858&nbsp;MPa).<ref>{{cite web |title=Deuterium, {{sup|2}}H |series=compounds |website=PubChem |publisher=U.S. [[National Institutes of Health]] |url=https://pubchem.ncbi.nlm.nih.gov/compound/deuterium}}</ref>

The physical properties of deuterium compounds can exhibit significant [[kinetic isotope effect]]s and other physical and chemical property differences from the protium analogs. {{sup|2}}H{{sub|2}}O, for example, is more [[viscous]] than normal {{H2O|link=y}}.<ref>{{RubberBible86th}}</ref> There are differences in bond energy and length for compounds of heavy hydrogen isotopes compared to protium, which are larger than the isotopic differences in any other element. Bonds involving deuterium and [[tritium]] are somewhat stronger than the corresponding bonds in protium, and these differences are enough to cause significant changes in biological reactions. Pharmaceutical firms are interested in the fact that {{sup|2}}H is harder to remove from carbon than {{sup|1}}H.<ref>{{cite news |last=Halford |first=Bethany | name-list-style = vanc |date=4 July 2016 |title=The deuterium switcheroo |newspaper=[[Chemical & Engineering News]] |volume=94 |issue=27 |publisher=[[American Chemical Society]] |pages=32–36 | doi = 10.1021/cen-09427-cover}}</ref>

Deuterium can replace {{sup|1}}H in water molecules to form heavy water ({{sup|2}}H{{sub|2}}O), which is about 10.6% denser than normal water (so that ice made from it sinks in normal water). Heavy water is slightly toxic in [[eukaryotic]] animals, with 25% substitution of the body water causing cell division problems and sterility, and 50% substitution causing death by cytotoxic syndrome (bone marrow failure and gastrointestinal lining failure). [[Prokaryotic]] organisms, however, can survive and grow in pure heavy water, though they develop slowly.<ref>{{cite journal | vauthors = Kushner DJ, Baker A, Dunstall TG | date = February 1999 | title = Pharmacological uses and perspectives of heavy water and deuterated compounds | journal = Canadian Journal of Physiology and Pharmacology | volume = 77 | issue = 2 | pages = 79–88 | pmid = 10535697 | doi = 10.1139/cjpp-77-2-79 }}</ref> Despite this toxicity, consumption of heavy water under normal circumstances does not pose a [[heavy water#Toxicity in humans|health threat]] to humans. It is estimated that a {{convert|70|kg|lb|0|abbr=on}} person might drink {{convert|4.8|L|USgal|abbr=out}} of heavy water without serious consequences.<ref>{{Cite book |chapter-url=https://books.google.com/books?id=nQh7iGX1geIC&pg=PA111 |isbn=978-1-4020-1314-0 |pages=111–112 |chapter=Physiological effect of heavy water |editor=Vertes, Attila |year=2003 |publisher=Kluwer |location=Dordrecht |title=Elements and isotopes: formation, transformation, distribution}}</ref> Small doses of heavy water (a few grams in humans, containing an amount of deuterium comparable to that normally present in the body) are routinely used as harmless metabolic tracers in humans and animals.