Ammonium

This article is about the molecular ion. For the ancient city, see Siwa Oasis.

Not to be confused with the neutral compound Ammonia.

Ammonium

Names
IUPAC name Ammonium
Systematic IUPAC name Azanium[1]
Identifiers
CAS Number	14798-03-9
3D model (JSmol)	Interactive image
ChEBI	CHEBI:CHEBI:28938
ChemSpider	218
MeSH	D000644
PubChem CID	16741146
InChI InChI=1S/H3N/h1H3/p+1 Key: QGZKDVFQNNGYKY-UHFFFAOYSA-O InChI=1/H3N/h1H3/p+1 Key: QGZKDVFQNNGYKY-IKLDFBCSAZ
SMILES [NH4+]
Properties
Chemical formula	NH+ 4
Molar mass	7001180390000000000♠18.039 g·mol−1
Acidity (pKa)	9.25
Conjugate base	Ammonia
Structure
Molecular shape	Tetrahedral
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

The ammonium cation is a positively charged polyatomic ion with the chemical formula NH⁺
₄. It is formed by the protonation of ammonia (NH₃). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary ammonium cations (NR⁺
₄), where one or more hydrogen atoms are replaced by organic groups (indicated by R).

Contents

• 
  1 Acid–base properties
  


• 
  2 Ammonium salts
  


• 
  3 Structure and bonding
  


• 
  4 Organic ammonium ions
  


• 
  5 Biology
  


• 
  6 Ammonium metal
  


• 
  7 See also
  


• 
  8 References
  

Acid–base properties

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 acids (proton donors):

H⁺ + NH₃ → NH⁺
₄

The ammonium ion is mildly acidic, reacting with Brønsted bases to return to the uncharged ammonia molecule:

NH⁺
₄ + B⁻ → HB + NH₃

Thus, treatment of concentrated solutions of ammonium salts with strong base gives ammonia. When ammonia is dissolved in water, a tiny amount of it converts to ammonium ions:

H₂O + NH₃ ⇌ OH⁻ + NH⁺
₄

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 ions is low), 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.

Ammonium salts

Formation of ammonium

Ammonium cation is found in a variety of salts 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. Such species are prepared by the electrolysis of an ammonium solution using a mercury cathode.^[2] This amalgam eventually decomposes to release ammonia and hydrogen.^[3]

Structure and bonding

The lone electron pair on the nitrogen atom (N) in ammonia, represented as a line above the N, forms the bond with a proton (H⁺). Thereafter, all four N–H bonds are equivalent, being polar covalent bonds. The ion has a tetrahedral structure and is isoelectronic with methane and borohydride. In terms of size, the ammonium cation (r_ionic = 175 pm) resembles the cesium cation (r_ionic = 183 pm).

Organic ammonium 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, secondary, tertiary, or quaternary. With the exception of the quaternary ammonium cations, the organic ammonium cations are weak acids.

An example of a reaction forming an ammonium ion is that between dimethylamine, (CH₃)₂NH, and an acid to give the dimethylaminium cation, (CH₃)₂NH⁺
₂:

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 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 surfactants.

An unusual class of organic ammonium salts are derivatives of amine radical cations, R₃N^+• such as tris(4-bromophenyl)ammonium hexachloroantimonate.

Biology

Main article: Excretion

Ammonium ions are a waste product of the metabolism of animals. In fish and aquatic invertebrates, it is excreted directly into the water. In mammals, sharks, and amphibians, it is converted in the urea cycle to urea, because urea is less toxic and can be stored more efficiently. In birds, reptiles, and terrestrial snails, metabolic ammonium is converted into uric acid, which is solid and can therefore be excreted with minimal water loss.^[4]

Ammonium is an important source of nitrogen for many plant species, especially those growing on hypoxic soils. However, it is also toxic to most crop species and is rarely applied as a sole nitrogen source.^[5]

Ammonium metal

The ammonium ion has very similar properties to the heavier alkali metals and is often considered a close relative.^[6][7][8] Ammonium is expected to behave as a metal (NH⁺
₄ ions in a sea of electrons) at very high pressures, such as inside gas giant planets such as Uranus and Neptune.^[7][8]

Under normal conditions, ammonium does not exist as a pure metal, but does as an amalgam (alloy with mercury).^[9]

See also

• Ammonium transporter


• f-ratio


• 
  Hydronium (H₃O⁺)


• Iminium


• Nitrification


• Onium compounds

References

1. 
   ^ International Union of Pure and Applied Chemistry (2005). Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005). Cambridge (UK): RSC–IUPAC. .mw-parser-output cite.citation{font-style:inherit}.mw-parser-output .citation q{quotes:"""""""'""'"}.mw-parser-output .citation .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .citation .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Wikisource-logo.svg/12px-Wikisource-logo.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-maint{display:none;color:#33aa33;margin-left:0.3em}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
   ISBN 0-85404-438-8. pp. 71,105,314. Electronic version.
   


2. 
   ^ Pseudo-binary compounds
   


3. 
   ^ "Ammonium Salts". VIAS Encyclopedia.
   


4. 
   ^ Campbell, Neil A.; Jane B. Reece (2002). "44". Biology (6th ed.). San Francisco: Pearson Education, Inc. pp. 937–938. ISBN 978-0-8053-6624-2.
   


5. 
   ^ Britto, DT; Kronzucker, HJ (2002). "NH₄⁺ toxicity in higher plants: a critical review" (PDF). Journal of Plant Physiology. 159 (6): 567–584. doi:10.1078/0176-1617-0774.
   


6. 
   ^ Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils, ed., Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, ISBN 0-12-352651-5
   


7. 
   ^ ^ab Stevenson, D. J. (November 20, 1975). "Does metallic ammonium exist?". Nature. 258 (5532): 222–223. Bibcode:1975Natur.258..222S. doi:10.1038/258222a0. Retrieved January 13, 2012.
   


8. 
   ^ ^ab Bernal, M. J. M.; Massey, H. S. W. (February 3, 1954). "Metallic Ammonium". Monthly Notices of the Royal Astronomical Society. 114 (2): 172–179. Bibcode:1954MNRAS.114..172B. doi:10.1093/mnras/114.2.172.
   


9. 
   ^ Reedy, J.H. (October 1, 1929). "Lecture demonstration of ammonium amalgam". Journal of Chemical Education. 6 (10): 1767. Bibcode:1929JChEd...6.1767R. doi:10.1021/ed006p1767.
   

v t e Molecules detected in outer space
Molecules	Diatomic Aluminium monochloride Aluminium monofluoride Aluminium monoxide Argonium Carbon monophosphide Carbon monosulfide Carbon monoxide Carborundum Cyanogen radical Diatomic carbon Fluoromethylidynium Hydrogen chloride Hydrogen fluoride Hydrogen (molecular) Hydroxyl radical Iron(II) oxide Magnesium monohydride cation Methylidyne radical Nitric oxide Nitrogen (molecular) Nitrogen monohydride Nitrogen sulfide Oxygen (molecular) Phosphorus monoxide Phosphorus mononitride Potassium chloride Silicon carbide Silicon mononitride Silicon monoxide Silicon monosulfide Sodium chloride Sodium iodide Sulfur monohydride Sulfur monoxide Titanium oxide Triatomic Aluminium hydroxide Aluminium isocyanide Amino radical Carbon dioxide Carbonyl sulfide CCP radical Chloronium Diazenylium Dicarbon monoxide Disilicon carbide Ethynyl radical Formyl radical Hydrogen cyanide (HCN) Hydrogen isocyanide (HNC) Hydrogen sulfide Hydroperoxyl Iron cyanide Isoformyl Magnesium cyanide Magnesium isocyanide Methylene radical N2H+ Nitrous oxide Nitroxyl Ozone Phosphaethyne Potassium cyanide Protonated molecular hydrogen Sodium cyanide Sodium hydroxide Silicon carbonitride c-Silicon dicarbide SiNC Sulfur dioxide Thioformyl Thioxoethenylidene Titanium dioxide Tricarbon Water Four atoms Acetylene Ammonia Cyanic acid Cyanoethynyl Cyclopropynylidyne Formaldehyde Fulminic acid HCCN Hydrogen peroxide Hydromagnesium isocyanide Isocyanic acid Isothiocyanic acid Ketenyl Methylene amidogen Methyl radical Propynylidyne Protonated carbon dioxide Protonated hydrogen cyanide Silicon tricarbide Thioformaldehyde Tricarbon monoxide Tricarbon sulfide Thiocyanic acid Five atoms Ammonium ion Butadiynyl Carbodiimide Cyanamide Cyanoacetylene Cyanoformaldehyde Cyanomethyl Cyclopropenylidene Formic acid Isocyanoacetylene Ketene Methane Methoxy radical Methylenimine Propadienylidene Protonated formaldehyde Protonated formaldehyde Silane Silicon-carbide cluster Six atoms Acetonitrile Cyanobutadiynyl radical E-Cyanomethanimine Cyclopropenone Diacetylene Ethylene Formamide HC4N Ketenimine Methanethiol Methanol Methyl isocyanide Pentynylidyne Propynal Protonated cyanoacetylene Seven atoms Acetaldehyde Acrylonitrile Vinyl cyanide Cyanodiacetylene Ethylene oxide Glycolonitrile Hexatriynyl radical Methylacetylene Methylamine Methyl isocyanate Vinyl alcohol Eight atoms Acetic acid Aminoacetonitrile Cyanoallene Ethanimine Glycolaldehyde Heptatrienyl radical Hexapentaenylidene Methylcyanoacetylene Methyl formate Propenal Nine atoms Acetamide Cyanohexatriyne Cyanotriacetylene Dimethyl ether Ethanol Methyldiacetylene Octatetraynyl radical Propene Propionitrile Ten atoms or more Acetone Benzene Benzonitrile Buckminsterfullerene (C60 fullerene, buckyball) C70 fullerene Cyanodecapentayne Cyanopentaacetylene Cyanotetra-acetylene Ethylene glycol Ethyl formate Methyl acetate Methyl-cyano-diacetylene Methyltriacetylene Propanal n-Propyl cyanide Pyrimidine
Deuterated molecules	Ammonia Ammonium ion Formaldehyde Formyl radical Heavy water Hydrogen cyanide Hydrogen deuteride Hydrogen isocyanide Methylacetylene N2D+ Trihydrogen cation
Unconfirmed	Anthracene Dihydroxyacetone Ethyl methyl ether Glycine Graphene H2NCO+ Linear C5 Naphthalene cation Phosphine Pyrene Silylidine
Related	Abiogenesis Astrobiology Astrochemistry Atomic and molecular astrophysics Chemical formula Circumstellar envelope Cosmic dust Cosmic ray Cosmochemistry Diffuse interstellar band Earliest known life forms Extraterrestrial life Extraterrestrial liquid water Forbidden mechanism Helium hydride ion Homochirality Intergalactic dust Interplanetary medium Interstellar medium Photodissociation region Iron–sulfur world theory Kerogen Molecules in stars Nexus for Exoplanet System Science Organic compound Outer space PAH world hypothesis Panspermia Polycyclic aromatic hydrocarbon (PAH) RNA world hypothesis Spectroscopy Tholin
Category:Astrochemistry Portal:Astrobiology

v t e Nitrogen species
Hydrides: NH3 NH4+ NH2− MNH2 N3− NH2OH N2H4 N3– Organic: -NH2 -CHR=NHR -CONHR2 HCN CN− C2N2 H2NCN CH2N2 Oxides: N2O NO NO2 N2O3 N2O4 N2O5 H2N2O2 H4N2O4 HNO2 HNO3 HONO3 HN2O2− N2O22− NO2− ONOO− NO3− NO43− O2NOO− NO+ NO2+ Halides: NF3 NCl3 NBr3 NI3 FN3 ClN3 BrN3 NH2Cl NHCl2
Chemical formulas

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