Editing Hydrogen (section)

==== Phases ====
[[File:Phase diagram of hydrogen.png|thumb|left|[[Phase diagram]] of hydrogen with a [[logarithmic scale]] The left edge corresponds about one atmosphere.<ref>{{Cite journal |last=Stevenson |first=D J |date=May 1982 |title=Interiors of the Giant Planets |url=https://www.annualreviews.org/doi/10.1146/annurev.ea.10.050182.001353 |journal=Annual Review of Earth and Planetary Sciences |language=en |volume=10 |issue=1 |pages=257–295 |doi=10.1146/annurev.ea.10.050182.001353 |bibcode=1982AREPS..10..257S |issn=0084-6597}}</ref>|alt=Phase diagram of hydrogen on logarithmic scales. Lines show boundaries between phases, with the end of the liquid-gas line indicating the critical point. The triple point of hydrogen is just off-scale to the left.]]
[[Liquid hydrogen]] can exist at temperatures below hydrogen's [[critical point (thermodynamics)|critical point]] of 33&nbsp;[[Kelvins|K]].<ref>{{cite web|url=https://webbook.nist.gov/cgi/cbook.cgi?ID=C1333740&Mask=4 |title=Hydrogen |website=NIST Chemistry WebBook, SRD 69 |publisher=[[National Institute of Standards and Technology]] |access-date=2025-01-14 |year=2023}}</ref> However, for it to be in a fully liquid state at [[atmospheric pressure]], H<sub>2</sub> needs to be cooled to {{convert|20.28|K|C F}}. Hydrogen was liquefied by [[James Dewar]] in 1898 by using [[regenerative cooling]] and his invention, the [[vacuum flask]].<ref>{{cite journal |author1=James Dewar |author1-link=James Dewar |title=Liquid Hydrogen |journal=Science |date=1900 |volume=11 |issue=278 |pages=641–651 |doi=10.1126/science.11.278.641 |pmid=17813562 |bibcode=1900Sci....11..641D |language=en}}</ref>

Liquid hydrogen becomes [[solid hydrogen]] at [[standard pressure]] below hydrogen's [[melting point]] of {{convert|14.01|K}}. Distinct solid phases exist, known as Phase I through Phase V, each exhibiting a characteristic molecular arrangement.<ref name="Helled2020">{{cite journal|first1=Ravit |last1=Helled |first2=Guglielmo |last2=Mazzola |first3=Ronald |last3=Redmer |title=Understanding dense hydrogen at planetary conditions |date=2020-09-01 |journal=Nature Reviews Physics |volume=2 |issue=10 |pages=562–574 |doi=10.1038/s42254-020-0223-3 |arxiv=2006.12219|bibcode=2020NatRP...2..562H }}</ref> Liquid and solid phases can exist in combination at the [[triple point]], a substance known as [[slush hydrogen]].<ref>{{cite book |last=Ohira |first=K. |chapter=Slush hydrogen production, storage, and transportation |date=2016 |title=Compendium of Hydrogen Energy |pages=53–90 |publisher=Elsevier |doi=10.1016/b978-1-78242-362-1.00003-1 |isbn=978-1-78242-362-1}}</ref>

[[Metallic hydrogen]], a phase obtained at extremely high pressures (in excess of {{convert|400|GPa|atm psi}}), is an electrical conductor. It is believed to exist deep within [[giant planet]]s like [[Jupiter]].<ref name="Helled2020"/><ref>{{cite book|last1=Frankoi |first1=A. |display-authors=etal |title=Astronomy 2e |year=2022 |publisher=OpenStax |chapter-url=https://openstax.org/books/astronomy-2e/pages/11-2-the-giant-planets |chapter=11.2 The Giant Planets |page=370 |isbn=978-1-951693-50-3}}</ref>

When [[ionization|ionized]], hydrogen becomes a [[plasma (physics)|plasma]]. This is the form in which hydrogen exists within [[star]]s.<ref>{{Cite book|last=Phillips |first=K. J. H. |date=1995 |title=Guide to the Sun |page=|publisher=[[Cambridge University Press]] |url=https://books.google.com/books?id=idwBChjVP0gC&q=Guide+to+the+Sun+phillips |isbn=978-0-521-39788-9 |url-status=live |archive-url= https://web.archive.org/web/20180115215631/https://books.google.com/books?id=idwBChjVP0gC&printsec=frontcover&dq=Guide+to+the+Sun+phillips&hl=en&sa=X&ved=0ahUKEwiBj4Gbj5bXAhXrrVQKHfnAAKUQ6AEIKDAA |archive-date=15 January 2018 }}</ref>