Editing Halogen (section)

===== Hydrogen halides =====
{{Main|Hydrogen halides}}
All of the halogens have been observed to react with hydrogen to form [[hydrogen halide]]s. For fluorine, chlorine, and bromine, this reaction is in the form of:

: H<sub>2</sub> + X<sub>2</sub> → 2HX

However, hydrogen iodide and hydrogen astatide can split back into their constituent elements.<ref name = "assorted">{{Cite web|author = Jim Clark|url = http://www.chemguide.co.uk/inorganic/group7/otherreactions.html|title = Assorted reactions of the halogens|year = 2011|access-date = February 27, 2013}}</ref>

The hydrogen-halogen reactions get gradually less reactive toward the heavier halogens. A fluorine-hydrogen reaction is explosive even when it is dark and cold. A chlorine-hydrogen reaction is also explosive, but only in the presence of light and heat. A bromine-hydrogen reaction is even less explosive; it is explosive only when exposed to flames. Iodine and astatine only partially react with hydrogen, forming [[Chemical equilibrium|equilibria]].<ref name = "assorted"/>

All halogens form binary compounds with hydrogen known as the hydrogen halides: [[hydrogen fluoride]] (HF), [[hydrogen chloride]] (HCl), [[hydrogen bromide]] (HBr), [[hydrogen iodide]] (HI), and [[hydrogen astatide]] (HAt). All of these compounds form acids when mixed with water. Hydrogen fluoride is the only hydrogen halide that forms [[hydrogen bond]]s. Hydrochloric acid, hydrobromic acid, hydroiodic acid, and {{not a typo|hydroastatic}} acid are all [[strong acid]]s, but hydrofluoric acid is a [[weak acid]].<ref>{{Cite web|author = Jim Clark|url = http://www.chemguide.co.uk/inorganic/group7/acidityhx.html|title = THE ACIDITY OF THE HYDROGEN HALIDES|year = 2002|access-date = February 24, 2013}}</ref>

All of the hydrogen halides are [[irritation|irritants]]. Hydrogen fluoride and hydrogen chloride are highly [[acid]]ic. Hydrogen fluoride is used as an [[Industry (economics) |indu]][[Manufacturing |strial]] chemical, and is highly toxic, causing [[pulmonary edema]] and damaging cells.<ref>{{Cite web|url = http://www.bt.cdc.gov/agent/hydrofluoricacid/basics/facts.asp|title = Facts about hydrogen fluoride|year = 2005|access-date = 2017-10-28|url-status = dead|archive-url = https://web.archive.org/web/20130201152726/http://www.bt.cdc.gov/agent/hydrofluoricacid/basics/facts.asp|archive-date = 2013-02-01}}</ref> Hydrogen chloride is also a dangerous chemical. Breathing in gas with more than fifty parts per million of hydrogen chloride can cause death in humans.<ref>{{Cite web|url = https://www.cdc.gov/niosh/idlh/7647010.html|title = Hydrogen chloride|access-date = February 24, 2013}}</ref> Hydrogen bromide is even more toxic and irritating than hydrogen chloride. Breathing in gas with more than thirty parts per million of hydrogen bromide can be lethal to humans.<ref>{{Cite web|url = https://www.cdc.gov/niosh/idlh/10035106.html|title = Hydrogen bromide|access-date = February 24, 2013}}</ref> Hydrogen iodide, like other hydrogen halides, is toxic.<ref>{{cite web | url = http://www.kumed.com/~/media/Imported/kumed/documents/kdhehydrogeniodide.ashx | title = Poison Facts:Low Chemicals: Hydrogen Iodid |access-date =2015-04-12}}</ref>