ammonium lauryl sulfate
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The ammonium cation is a positively-charged
polyatomic ion A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zero. The term molecule may or may no ...
with the
chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbol ...
or . It is formed by the
protonation In chemistry, protonation (or hydronation) is the adding of a proton (or hydron, or hydrogen cation), (H+) to an atom, molecule, or ion, forming a conjugate acid. (The complementary process, when a proton is removed from a Brønsted–Lowry acid ...
of
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
(). Ammonium is also a general name for positively charged or protonated substituted
amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen Hydrogen is the chemical element wi ...
s and quaternary ammonium cations (), where one or more
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
atoms are replaced by organic groups (indicated by R).


Acid–base properties

The ammonium ion is generated when ammonia, a weak base, reacts with Brønsted acids (proton donors): :H+ + NH3 -> H4 The ammonium ion is mildly acidic, reacting with Brønsted bases to return to the uncharged ammonia molecule: : H4 + 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- + H4 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 A hydrogen ion is created when a hydrogen atom loses or gains an electron. A positively charged hydrogen ion (or proton) can readily combine with other particles and therefore is only seen isolated when it is in a gaseous state or a nearly particle ...
s is low and hydroxide ions is high), the equilibrium shifts to the left: the
hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. I ...
ion abstracts a proton from the ammonium ion, generating ammonia. Formation of ammonium compounds can also occur in the
vapor In physics, a vapor (American English) or vapour (British English and Canadian English; see spelling differences) is a substance in the gas phase at a temperature lower than its critical temperature,R. H. Petrucci, W. S. Harwood, and F. G. Her ...
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 Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structural ...
in a thin white layer on surfaces.


Salts

Ammonium cation is found in a variety of
salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...
s such as
ammonium carbonate Ammonium carbonate is a salt with the chemical formula (NH4)2CO3. Since it readily degrades to gaseous ammonia and carbon dioxide upon heating, it is used as a leavening agent and also as smelling salt. It is also known as baker's ammonia and is ...
, ammonium chloride and
ammonium nitrate Ammonium nitrate is a chemical compound with the chemical formula . It is a white crystalline salt consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, although it does not form hydrates. It is ...
. Most simple ammonium salts are very
soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubi ...
in water. An exception is
ammonium hexachloroplatinate Ammonium hexachloroplatinate, also known as ammonium chloroplatinate, is the inorganic compound with the formula (NH4)2 tCl6 It is a rare example of a soluble platinum(IV) salt that is not hygroscopic. It forms intensely yellow solutions in water. ...
, the formation of which was once used as a test for ammonium. The ammonium salts of nitrate and especially
perchlorate A perchlorate is a chemical compound containing the perchlorate ion, . The majority of perchlorates are commercially produced salts. They are mainly used as oxidizers for pyrotechnic devices and to control static electricity in food packaging. Per ...
are highly explosive, in these cases ammonium is the reducing agent. In an unusual process, ammonium ions form an
amalgam Amalgam most commonly refers to: * Amalgam (chemistry), mercury alloy * Amalgam (dentistry), material of silver tooth fillings ** Bonded amalgam, used in dentistry Amalgam may also refer to: * Amalgam Comics, a publisher * Amalgam Digital ...
. Such species are prepared by the addition of sodium amalgam to a solution of ammonium chloride. This amalgam eventually decomposes to release ammonia and hydrogen. To find whether the ammonium ion is present in the salt, first the salt is heated in presence of
alkali hydroxide The alkali hydroxides are a class of chemical compounds which are composed of an alkali metal cation and the hydroxide anion (OH−). The alkali hydroxides are: * Lithium hydroxide (LiOH) * Sodium hydroxide (NaOH) * Potassium hydroxide (KOH) *Rubi ...
releasing a gas with characteristic smell which of course is
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
. : H4 + OH- -> eatNH3 + H2O To further confirm ammonia it passed through glass rod dipped in HCl solution (
hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid Acid strength is the tendency of an acid, symbol ...
) creating white dense fumes of ammonium chloride. :NH3_ + HCl_ -> H4l_ Ammonia when passed through (
copper(II) sulphate Copper(II) sulfate, also known as copper sulphate, is an inorganic compound with the chemical formula . It forms hydrates , where ''n'' can range from 1 to 7. The pentahydrate (''n'' = 5), a bright blue crystal, is the most commonly encountered hy ...
) solution turns from blue to deep blue color forming
Schweizer's reagent Schweizer's reagent is the metal ammine complex with the formula u(NH3)4(H2O)2OH)2. This deep-blue compound is used in purifying cellulose. It is prepared by precipitating copper(II) hydroxide from an aqueous solution of copper sulfate using so ...
. :CuSO4_ + 4 NH3_ + 4 H2O ->
u(NH3)4(H2O)2 U or u, is the twenty-first and sixth-to-last Letter (alphabet), letter and fifth vowel letter of the Latin alphabet, used in the English alphabet, modern English alphabet, the alphabets of other western European languages and others worldwide ...
OH)2_ + H2SO4_
Ammonia or ammonium ion when added to Nessler's reagent gives brown color precipitate known as iodide of Million's base in basic medium. Ammonium ion when added to chloroplatinic acid gives a yellow precipitate. :H2 tCl6 + H4_ -> H4 tCl6 + 2 H+ Ammonium ion when added to sodium cobaltinitrite gives a yellow precipitate. :Na3 o(NO2)6 + 3 H4_ -> H4 o(NO2)6 + 3 Na+_ Ammonium ion when added to
potassium bitartrate Potassium bitartrate, also known as potassium hydrogen tartrate, with formula K C4 H5 O6, is a byproduct of winemaking. In cooking, it is known as cream of tartar. It is processed from the potassium acid salt of tartaric acid (a carboxylic ac ...
gives a white precipitate. :KC4H5O6_ + H4_ -> H44H5O6_ + K+_


Structure and bonding

The lone electron pair on the
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
atom (N) in ammonia, represented as a line above the N, forms the bond with a proton (). Thereafter, all four N–H bonds are equivalent, being polar covalent bonds. The ion has a tetrahedral structure and is
isoelectronic Isoelectronicity is a phenomenon observed when two or more molecules have the same structure (positions and connectivities among atoms) and the same electronic configurations, but differ by what specific elements are at certain locations in th ...
with
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
and the
borohydride Borohydride refers to the anion , which is also called tetrahydroborate, and its salts. Borohydride or hydroborate is also the term used for compounds containing , where ''n'' is an integer from 0 to 3, for example cyanoborohydride or cyanotrihyd ...
anion. In terms of size, the ammonium cation (''r''ionic = 175 pm) resembles the caesium cation (''r''ionic = 183 pm).


Organic ions

The hydrogen atoms in the ammonium ion can be substituted with an
alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloa ...
group or some other organic group to form a substituted ammonium ion (
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
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 Dimethylamine is an organic compound with the formula (CH3)2NH. This secondary amine is a colorless, flammable gas with an ammonia-like odor. Dimethylamine is commonly encountered commercially as a solution in water at concentrations up to aroun ...
, , and an acid to give the
dimethylammonium Dimethylamine is an organic compound with the formula (CH3)2NH. This secondary amine is a colorless, flammable gas with an ammonia-like odor. Dimethylamine is commonly encountered commercially as a solution in water at concentrations up to aroun ...
cation, : : 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, such as tris(4-bromophenyl)ammoniumyl hexachloroantimonate.


Biology

Ammonium ions are a waste product of the
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run c ...
of
animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
s. In fish and aquatic invertebrates, it is excreted directly into the water. In mammals,
shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...
s, and amphibians, it is converted in the
urea cycle The urea cycle (also known as the ornithine cycle) is a cycle of Biochemistry, biochemical reactions that produces urea (NH2)2CO from ammonia (NH3). Animals that use this cycle, mainly amphibians and mammals, are called ureotelic. The urea cycle ...
to
urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important ...
, because urea is less toxic and can be stored more efficiently. In birds, reptiles, and terrestrial snails, metabolic ammonium is converted into
uric acid Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C5H4N4O3. It forms ions and salts known as urates and acid urates, such as ammonium acid urate. Uric acid is a product of the metabolic breakdown ...
, which is solid and can therefore be excreted with minimal water loss. 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.


Metal

The ammonium ion has very similar properties to the heavier alkali metals cations and is often considered a close equivalent. Ammonium is expected to behave as a metal ( ions in a sea of electrons) at very high pressures, such as inside gas giant planets such as
Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus ( Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and father of ...
and Neptune. Under normal conditions, ammonium does not exist as a pure metal, but does as an
amalgam Amalgam most commonly refers to: * Amalgam (chemistry), mercury alloy * Amalgam (dentistry), material of silver tooth fillings ** Bonded amalgam, used in dentistry Amalgam may also refer to: * Amalgam Comics, a publisher * Amalgam Digital ...
(alloy with mercury).


See also

*
Ammonium transporter Ammonia transportersTC# 1.A.11 are structurally related membrane transport proteins called Amt proteins (ammonia transporters) in bacteria and plants, methylammonium/ammonium permeases (MEPs) in yeast, or Rhesus (Rh) proteins in chordates. In huma ...
* f-ratio *
Hydronium In chemistry, hydronium (hydroxonium in traditional British English) is the common name for the aqueous cation , the type of oxonium ion produced by protonation of water. It is often viewed as the positive ion present when an Arrhenius acid i ...
(H3O+) *
Iminium In organic chemistry, an iminium cation is a polyatomic ion with the general structure . They are common in synthetic chemistry and biology. Structure Iminium cations adopt alkene-like geometries. The central C=N unit is nearly coplanar with al ...
*
Nitrification ''Nitrification'' is the biological oxidation of ammonia to nitrite followed by the oxidation of the nitrite to nitrate occurring through separate organisms or direct ammonia oxidation to nitrate in comammox bacteria. The transformation of am ...
*
Onium compounds In chemistry, an onium ion is a cation formally obtained by the protonation of mononuclear parent hydride of a pnictogen (group 15 of the periodic table), chalcogen (group 16), or halogen (group 17). The oldest-known onium ion, and the namesake ...
* The Magnificent Possession (Isaac Asimov short story)


References

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