Editing Ammonium

{{about|the ammonium ion|its neutral conjugate base|ammonia}}
{{About|the molecular ion|the ancient city|Siwa Oasis}}
{{Chembox
| ImageFile1     = Ammonium-2D.svg
| ImageClass1    = skin-invert
| ImageSize1     = 170px
| ImageAlt1      = 2-D skeletal version of the ammonium ion
| ImageFileL1    = Ammonium-3D-balls.png
| ImageAltL1     = [[Ball-and-stick model]] of the ammonium cation
| ImageFileR1    = Ammonium-3D-vdW.png
| ImageAltR1     = Space-filling model of the ammonium cation
| SystematicName = Azanium<ref>{{RedBookRef|pages=71,105,314}}</ref>
| IUPACName      = Ammonium ion
| OtherNames     = 
| Section1       = {{Chembox Identifiers
 | CASNo = 14798-03-9
 | CASNo_Ref = {{cascite|correct|CAS}}
 | UNII_Ref = {{fdacite|correct|FDA}}
 | UNII = 54S68520I4
 | PubChem = 16741146
 | ChemSpiderID = 218
 | SMILES = [NH4+]
 | InChI = 1/H3N/h1H3/p+1
 | InChIKey = QGZKDVFQNNGYKY-IKLDFBCSAZ
 | StdInChI = 1S/H3N/h1H3/p+1
 | StdInChIKey = QGZKDVFQNNGYKY-UHFFFAOYSA-O
 | RTECS = 
 | MeSHName = D000644
 | ChEBI = 28938
 }}
| Section2       = {{Chembox Properties
 | Formula = {{chem2|[NH4]+}}
 | N=1|H=4
 | pKa = 9.25
 | ConjugateBase = [[Ammonia]]
 }}
| Section3       = {{Chembox Structure
 | MolShape = [[Tetrahedral molecular geometry|Tetrahedral]]
 }}
| Section9       = {{Chembox Related
 | OtherCompounds = Ammonium radical •NH4
 | OtherCations = {{ubl|[[Phosphonium]] {{chem2|[PH4]+}}|[[Arsonium]] {{chem2|[AsH4]+}}|[[Hydronium]] {{chem2|[H3O]+}}|[[Sulfonium]] {{chem2|[H3S]+}}|[[Fluoronium]] {{chem2|[H2F]+}}|[[Chloronium]] {{chem2|[H2Cl]+}}|[[Bromonium]] {{chem2|[H2Br]+}}|[[Iodonium]] {{chem2|[H2I]+}}|[[Carbonium]] {{chem2|[CH5]+}}|[[Trihydrogen cation]] {{chem2|[H3]+}}}}
 }}
}}

'''Ammonium''' is a modified form of [[ammonia]] that has an extra hydrogen atom.  It is a positively charged ([[cation]]ic) [[polyatomic ion|molecular ion]] with the [[chemical formula]] {{chem2|NH4+}} or {{chem2|[NH4]+}}. It is formed by the [[protonation|addition of a proton]] (a hydrogen nucleus) to ammonia ({{chem2|NH3}}). Ammonium is also a general name for positively charged (protonated) substituted [[amine]]s and [[quaternary ammonium cation]]s ({{chem2|[NR4]+}}), where one or more [[hydrogen]] [[atoms]] are replaced by [[Organic compound|organic]] or other groups (indicated by R). Not only is ammonium a source of [[nitrogen]] and a key [[metabolite]] for many living organisms, but it is an integral part of the global [[nitrogen cycle]].<ref name=":02">{{Citation |last1=Schlesinger |first1=William H. |title=Chapter 12 - The Global Cycles of Nitrogen, Phosphorus and Potassium |date=2020-01-01 |work=Biogeochemistry (Fourth Edition) |pages=483–508 |editor-last=Schlesinger |editor-first=William H. |url=https://www.sciencedirect.com/science/article/pii/B9780128146088000128 |access-date=2024-03-08 |publisher=Academic Press |doi=10.1016/b978-0-12-814608-8.00012-8 |isbn=978-0-12-814608-8 |last2=Bernhardt |first2=Emily S. |editor2-last=Bernhardt |editor2-first=Emily S.}}</ref> As such, human impact in recent years could have an effect on the biological communities that depend on it.

== Acid–base properties ==
[[File:Hydrochloric acid ammonia.jpg|thumb|Fumes from [[hydrochloric acid]] and ammonia forming a white cloud of [[ammonium chloride]]]]

The ammonium ion is generated when ammonia, a weak base, reacts with [[Brønsted–Lowry acid–base theory|Brønsted acids]] ([[proton]] donors):
: {{chem2|H+ + NH3 → [NH4]+}}
The ammonium ion is mildly acidic, reacting with Brønsted bases to return to the uncharged ammonia molecule:
: {{chem2|[NH4]+ + B- → HB + NH3}}
Thus, the treatment of concentrated solutions of ammonium salts with a strong base gives ammonia. When ammonia is dissolved in water, a tiny amount of it converts to ammonium ions:
: {{chem2|H2O + NH3 ⇌ OH- + [NH4]+}}

The degree to which ammonia forms the ammonium ion depends on the [[pH]] of the solution. If the pH is low, the equilibrium shifts to the right: more ammonia molecules are converted into ammonium ions. If the pH is high (the concentration of [[hydrogen ion]]s is low and [[hydroxide ion]]s is high), the equilibrium shifts to the left: the [[hydroxide]] ion abstracts a proton from the ammonium ion, generating ammonia.

Formation of ammonium compounds can also occur in the [[vapor]] phase; for example, when ammonia vapor comes in contact with hydrogen chloride vapor, a white cloud of ammonium chloride forms, which eventually settles out as a [[solid]] in a thin white layer on surfaces.

== Salts and characteristic reactions ==
[[File:Bildung Ammonium.svg|thumb|Formation of ammonium]]
Ammonium cation is found in a variety of [[salt (chemistry)|salt]]s such as [[ammonium carbonate]], [[ammonium chloride]], and [[ammonium nitrate]]. Most simple ammonium salts are very [[soluble]] in water. An exception is [[ammonium hexachloroplatinate]], the formation of which was once used as a test for ammonium. The ammonium salts of nitrate and especially [[perchlorate]] are highly explosive, in these cases, ammonium is the reducing agent.

In an unusual process, ammonium ions form an [[amalgam (chemistry)|amalgam]]. Such species are prepared by the addition of sodium amalgam to a solution of ammonium chloride.<ref>{{Cite web |url=http://www.hull.ac.uk/chemistry/intro_inorganic/Chap9.htm |title=Pseudo-binary compounds |access-date=2007-10-12 |archive-date=2020-07-27 |archive-url=https://web.archive.org/web/20200727215402/https://www.hull.ac.uk/chemistry/intro_inorganic/Chap9.htm |url-status=dead }}</ref> This amalgam eventually decomposes to release ammonia and hydrogen.<ref>{{cite encyclopedia|encyclopedia = VIAS Encyclopedia|title = Ammonium Salts |url = http://www.vias.org/encyclopedia/chem_ammonia_salts.html}}</ref>

To find whether the ammonium ion is present in the salt, first, the salt is heated in presence of [[alkali hydroxide]] releasing a gas with a characteristic smell, which is [[ammonia]].
: {{chem2|[NH4]+ + OH-}} {{overset|''heat''|→}} {{chem2|NH3 + H2O}}

To further confirm ammonia, it is passed through a glass rod dipped in an {{Chem2|HCl}} solution ([[hydrochloric acid]]), creating white dense fumes of [[ammonium chloride]].
: {{chem2|NH3(g) + HCl(aq) → [NH4]Cl(s)}}

Ammonia, when passed through {{chem2|CuSO4}} ([[copper(II) sulfate]]) solution, changes its color from blue to deep blue, forming [[Schweizer's reagent]].
: {{chem2|CuSO4(aq) + 4 NH3(aq) + 4 H2O → [Cu(NH3)4(H2O)2](OH)2(aq) + H2SO4(aq)}}

Ammonia or ammonium ion when added to [[Nessler's reagent]] gives a brown color precipitate known as the iodide of Million's base in basic medium.

Ammonium ion when added to [[chloroplatinic acid]] gives a yellow precipitate of [[Ammonium hexachloroplatinate|ammonium hexachloroplatinate(IV)]].
: {{chem2|H2[PtCl6](aq) + [NH4]+(aq) → [NH4]2[PtCl6](s) + 2 H+}}

Ammonium ion when added to [[sodium cobaltinitrite]] gives a yellow precipitate of ammonium cobaltinitrite.
: {{chem2|Na3[Co(NO2)6](aq) + 3 [NH4]+(aq) → [NH4]3[Co(NO2)6](s) + 3 Na+(aq)}}

Ammonium ion gives a white precipitate of ammonium bitartrate when added to [[potassium bitartrate]].
: {{chem2|KC4H5O6(aq) + [NH4]+(aq) → [NH4]C4H5O6(s) + K+(aq)}}

== Structure and bonding ==
{{More citations needed|section|date=March 2022}}
The [[lone pair|lone electron pair]] on the [[nitrogen]] atom (N) in ammonia, represented as a line above the N, forms a [[Coordinate covalent bond|coordinate bond]] with a [[proton]] ({{chem2|H+}}). After that, all four {{chem2|N\sH}} bonds are equivalent, being polar [[covalent bond]]s. The ion has a [[tetrahedral molecular geometry|tetrahedral structure]] and is [[isoelectronicity|isoelectronic]] with [[methane]] and the [[borohydride]] anion. In terms of size, the ammonium cation (''r''<sub>ionic</sub>&nbsp;=&nbsp;175&nbsp;pm){{Citation needed|date=March 2022}} resembles the [[caesium]] cation (''r''<sub>ionic</sub>&nbsp;=&nbsp;183&nbsp;pm).{{Citation needed|date=March 2022}}

== Organic ions ==
{{See also|Amine}}
The hydrogen atoms in the ammonium ion can be substituted with an [[alkyl]] group or some other organic group to form a '''substituted ammonium ion''' ([[IUPAC]] nomenclature: '''aminium ion'''). Depending on the number of organic groups, the ammonium cation is called a [[Primary (chemistry)|primary]], [[Secondary (chemistry)|secondary]], [[Tertiary (chemistry)|tertiary]], or [[Quaternary (chemistry)|quaternary]]. Except the quaternary ammonium cations, the organic ammonium cations are weak acids.

An example of a reaction forming an ammonium ion is that between [[dimethylamine]], {{chem2|(CH3)2NH}}, and an acid to give the [[dimethylammonium]] cation, {{chem2|[(CH3)2NH2]+}}:
: [[File:Dimethylammonium-formation-2D.png|class=skin-invert-image|400px]]

Quaternary ammonium cations have four organic groups attached to the nitrogen atom, they lack a hydrogen atom bonded to the nitrogen atom. These cations, such as the [[tetra-n-butylammonium|tetra-''n''-butylammonium]] cation, are sometimes used to replace sodium or potassium ions to increase the [[solubility]] of the associated anion in organic [[solvents]]. Primary, secondary, and tertiary ammonium salts serve the same function but are less [[lipophilic]]. They are also used as [[phase-transfer catalysts]] and [[surfactant]]s.

An unusual class of organic ammonium salts is derivatives of amine [[radical (chemistry)|radical]] cations, {{chem2|[•NR3]+}} such as [[tris(4-bromophenyl)ammoniumyl hexachloroantimonate]].

== Biology ==
{{Main|Excretion}}
[[File:Nitrogen Cycle 2.svg|thumb|293x293px|Ammonium exists as a result of ammonification and [[decomposer]]s. Ammonium is eventually nitrified, where it contributes to the flow of [[nitrogen]] through the ecosystem. Human impacts are not shown here, but can impact the global [[nitrogen cycle]].]]
Because [[nitrogen]] often limits net [[primary production]] due to its use in [[enzyme]]s that mediate the biochemical reactions that are necessary for life, ammonium is utilized by some microbes and plants.<ref name=":03">{{Citation |last1=Schlesinger |first1=William H. |title=Chapter 12 - The Global Cycles of Nitrogen, Phosphorus and Potassium |date=2020-01-01 |work=Biogeochemistry (Fourth Edition) |pages=483–508 |editor-last=Schlesinger |editor-first=William H. |url=https://www.sciencedirect.com/science/article/pii/B9780128146088000128 |access-date=2024-03-08 |publisher=Academic Press |doi=10.1016/b978-0-12-814608-8.00012-8 |isbn=978-0-12-814608-8 |last2=Bernhardt |first2=Emily S. |editor2-last=Bernhardt |editor2-first=Emily S.}}</ref> For example, energy is released by the [[Redox|oxidation]] of ammonium in a process known as [[nitrification]], which produces [[nitrate]] and [[nitrite]].<ref name=":1">{{Cite journal |last=Rosswall |first=T. |date=1982 |title=Microbiological regulation of the biogeochemical nitrogen cycle / Regulación microbiana del ciclo bíogeoquímico del nitrógeno |url=https://www.jstor.org/stable/42934020 |journal=Plant and Soil |volume=67 |issue=1/3 |pages=15–34 |doi=10.1007/BF02182752 |jstor=42934020 |issn=0032-079X}}</ref> This process is a form of [[Auxotrophy|autotrophy]] that is common amongst ''[[Nitrosomonas]]'', ''[[Nitrobacter]]'', ''[[Nitrosolobus]]'', and ''[[Nitrosospira]]'', amongst others.<ref name=":1" />

The amount of ammonium in soil that is available for [[nitrification]] by microbes varies depending on environmental conditions.<ref>{{Cite journal |last1=Barsdate |first1=Robert J. |last2=Alexander |first2=Vera |date=January 1975 |title=The Nitrogen Balance of Arctic Tundra: Pathways, Rates, and Environmental Implications |url=https://acsess.onlinelibrary.wiley.com/doi/10.2134/jeq1975.00472425000400010025x |journal=Journal of Environmental Quality |language=en |volume=4 |issue=1 |pages=111–117 |doi=10.2134/jeq1975.00472425000400010025x |bibcode=1975JEnvQ...4..111B |issn=0047-2425}}</ref><ref>{{Cite journal |last1=Nadelhoffer |first1=Knute J. |last2=Aber |first2=John D. |last3=Melillo |first3=Jerry M. |date=1984-10-01 |title=Seasonal patterns of ammonium and nitrate uptake in nine temperate forest ecosystems |url=https://doi.org/10.1007/BF02140039 |journal=Plant and Soil |language=en |volume=80 |issue=3 |pages=321–335 |doi=10.1007/BF02140039 |bibcode=1984PlSoi..80..321N |issn=1573-5036}}</ref> For example, ammonium is deposited as a waste product from some animals, although it is converted into [[urea]] in mammals, sharks, and amphibians, and into [[uric acid]] in birds, reptiles, and terrestrial snails.<ref>{{Cite book |last1=Campbell |first1=Neil A. |url=http://archive.org/details/biologyc00camp |title=Biology |last2=Reece |first2=Jane B. |date=2002 |publisher=San Francisco : Benjamin Cummings |others=Internet Archive |isbn=978-0-8053-6624-2}}</ref> Its availability in soils is also influenced by [[Mineralization (soil science)|mineralization]], which makes more ammonium available from organic [[nitrogen]] sources, and [[Immobilization (soil science)|immobilization]], which sequesters ammonium into organic [[nitrogen]] sources, both of which are mitigated by biological factors.<ref name=":1" />

Conversely, [[nitrate]] and [[nitrite]] can be reduced to ammonium as a way for living organisms to access [[nitrogen]] for growth in a process known as assimilatory nitrate reduction.<ref name=":2">{{Cite journal |last1=Tiedje |first1=J. M. |last2=Sørensen |first2=J. |last3=Chang |first3=Y.-Y. L. |date=1981 |title=Assimilatory and Dissimilatory Nitrate Reduction: Perspectives and Methodology for Simultaneous Measurement of Several Nitrogen Cycle Processes |url=https://www.jstor.org/stable/45128674 |journal=Ecological Bulletins |issue=33 |pages=331–342 |jstor=45128674 |issn=0346-6868}}</ref> Once assimilated, it can be incorporated into [[protein]]s and [[DNA]].<ref>{{Cite journal |last1=Llácer |first1=José L |last2=Fita |first2=Ignacio |last3=Rubio |first3=Vicente |date=2008-12-01 |title=Arginine and nitrogen storage |url=https://www.sciencedirect.com/science/article/pii/S0959440X08001541 |journal=Current Opinion in Structural Biology |series=Catalysis and regulation / Proteins |volume=18 |issue=6 |pages=673–681 |doi=10.1016/j.sbi.2008.11.002 |pmid=19013524 |issn=0959-440X|hdl=10261/111022 |hdl-access=free }}</ref>

Ammonium can accumulate in soils where [[nitrification]] is slow or inhibited, which is common in hypoxic soils.<ref>{{Cite journal |last1=Wang |first1=Lixin |last2=Macko |first2=Stephen A. |date=March 2011 |title=Constrained preferences in nitrogen uptake across plant species and environments |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1365-3040.2010.02260.x |journal=Plant, Cell & Environment |language=en |volume=34 |issue=3 |pages=525–534 |doi=10.1111/j.1365-3040.2010.02260.x |pmid=21118424 |issn=0140-7791}}</ref> For example, ammonium mobilization is one of the key factors for the [[Symbiosis|symbiotic]] association between plants and fungi, called [[mycorrhiza]]e.<ref>{{Cite journal |last1=Hodge |first1=Angela |last2=Storer |first2=Kate |date=2015-01-01 |title=Arbuscular mycorrhiza and nitrogen: implications for individual plants through to ecosystems |url=https://doi.org/10.1007/s11104-014-2162-1 |journal=Plant and Soil |language=en |volume=386 |issue=1 |pages=1–19 |doi=10.1007/s11104-014-2162-1 |bibcode=2015PlSoi.386....1H |issn=1573-5036}}</ref> However, plants that consistently utilize ammonium as a [[nitrogen]] source often must invest into more extensive root systems due to ammonium's limited mobility in soils compared to other [[nitrogen]] sources.<ref>{{Cite journal |last1=Raven |first1=John A. |last2=Linda |first2=Bernd Wollenweber |last3=Handley |first3=L. |date=May 1992 |title=Ammonia and ammonium fluxes between photolithotrophs and the environment in relation to the global nitrogen cycle |url=https://nph.onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.1992.tb01087.x |journal=New Phytologist |language=en |volume=121 |issue=1 |pages=5–18 |doi=10.1111/j.1469-8137.1992.tb01087.x |issn=0028-646X}}</ref><ref>{{Cite journal |last1=Bloom |first1=A. J. |last2=Jackson |first2=L. E. |last3=Smart |first3=D. R. |date=March 1993 |title=Root growth as a function of ammonium and nitrate in the root zone |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1365-3040.1993.tb00861.x |journal=Plant, Cell & Environment |language=en |volume=16 |issue=2 |pages=199–206 |doi=10.1111/j.1365-3040.1993.tb00861.x |issn=0140-7791}}</ref>

== Human impact ==
Ammonium deposition from the atmosphere has increased in recent years due to volatilization from livestock waste and increased fertilizer use.<ref>{{Cite journal |last1=Ackerman |first1=Daniel |last2=Millet |first2=Dylan B. |last3=Chen |first3=Xin |date=January 2019 |title=Global Estimates of Inorganic Nitrogen Deposition Across Four Decades |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GB005990 |journal=Global Biogeochemical Cycles |language=en |volume=33 |issue=1 |pages=100–107 |doi=10.1029/2018GB005990 |bibcode=2019GBioC..33..100A |issn=0886-6236}}</ref> Because net [[primary production]] is often limited by [[nitrogen]], increased ammonium levels could impact the biological communities that rely on it. For example, increasing [[nitrogen]] content has been shown to increase plant growth, but aggravate soil phosphorus levels, which can impact microbial communities.<ref>{{Cite journal |last1=Dong |first1=Junfu |last2=Cui |first2=Xiaoyong |last3=Niu |first3=Haishan |last4=Zhang |first4=Jing |last5=Zhu |first5=Chuanlu |last6=Li |first6=Linfeng |last7=Pang |first7=Zhe |last8=Wang |first8=Shiping |date=2022-06-20 |title=Effects of Nitrogen Addition on Plant Properties and Microbiomes Under High Phosphorus Addition Level in the Alpine Steppe |journal=Frontiers in Plant Science |volume=13 |doi=10.3389/fpls.2022.894365 |doi-access=free |issn=1664-462X |pmc=9251499 |pmid=35795351}}</ref>

== Metal ==
The ammonium cation has very similar properties to the heavier [[alkali metal]] cations and is often considered a close equivalent.<ref name = "Holleman&Wiberg">{{Holleman&Wiberg}}</ref><ref name="Stevenson" /><ref name="Bernal&Massey" /> Ammonium is expected to behave as a [[metal]] ({{chem2|[NH4]+}} ions in a sea of [[electrons]]) at very high pressures, such as inside [[giant planet]]s such as [[Uranus]] and [[Neptune]].<ref name="Stevenson">{{cite journal |last1=Stevenson |first1=D. J. |date=November 20, 1975 |title=Does metallic ammonium exist? |journal=[[Nature (journal)|Nature]] |volume=258 |issue= 5532|pages=222–223 |doi=10.1038/258222a0 |bibcode = 1975Natur.258..222S |s2cid=4199721 }}</ref><ref name="Bernal&Massey">{{cite journal |last1=Bernal |first1=M. J. M. |last2=Massey |first2=H. S. W. |date=February 3, 1954 |title=Metallic Ammonium |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=114 |issue= 2|pages=172–179 |bibcode=1954MNRAS.114..172B |doi=10.1093/mnras/114.2.172|doi-access=free }}</ref>

Under normal conditions, ammonium does not exist as a pure metal but does as an [[amalgam (chemistry)|amalgam]] (alloy with [[mercury (element)|mercury]]).<ref>{{cite journal |last1=Reedy |first1=J.H.|date=October 1, 1929|title=Lecture demonstration of ammonium amalgam |journal=Journal of Chemical Education |volume=6 |issue=10 |pages=1767 |doi=10.1021/ed006p1767|bibcode=1929JChEd...6.1767R}}</ref>

== See also ==
* [[Onium compounds]]
* [[Fluoronium]], ({{chem2|[H2F]+}} and substituted derivatives)
* [[Oxonium ion|Oxonium]] ({{chem2|[R3O]+}}, where R is typically [[hydrogen]] or [[organyl]])
* [[Hydronium]] ({{chem2|[H3O]+}}, the simplest oxonium ion)
* [[Quaternary ammonium cation]] ({{chem2|[NR4]+}}, where R is organyl)
* [[Tetrafluoroammonium]] ({{chem2|[NF4]+}})
* [[Hydrazinium]] ({{chem2|[H2N\sNH3]+}} and substituted derivatives)
* [[Hydrazinium|Hydrazinediium]] ({{chem2|[H3N\sNH3](2+)}} and substituted derivatives)
* [[Iminium]] ({{chem2|[H2C\dNH2]+}} and substituted derivatives)
* [[Diazonium compound|Diazonium]] ({{chem2|[H\sN\tN]+}} and substituted derivatives)
* [[Diimide#Related|Diazynediium]] ({{chem2|[H\sN\tN\sH](2+)}} and substituted derivatives)
* [[Hydrazoic acid#Reactions|Aminodiazonium]] ({{chem2|[H2N\dN\dN]+ ⇌ [H2N\sN\tN]+}} and substituted derivatives)
* [[Hydroxylamine|Hydroxylammonium]] ({{chem2|[HO\sNH3]+}} and substituted derivatives)<!--Please make an article/a section about the hydroxylammonium ion-->
* [[Ammonium transporter]]
* [[f-ratio (oceanography)|f-ratio]]
* [[Nitrification]]
* [[The Magnificent Possession]] (Isaac Asimov short story)
* [[Ammonia solution|Ammonium hydroxide]]

== References ==
{{Reflist|30em}}

{{Ammonium salts}}
{{Molecules detected in outer space}}
{{Nitrogen compounds}}
{{Authority control}}

[[Category:Ammonium compounds|*]]
[[Category:Cations]]