Ammonium

Ammonium

Overview

The ammonium cation is a positively charged
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...

 polyatomic cation
Polyatomic ion
A polyatomic ion, also known as a molecular ion, is a charged species composed of two or more atoms covalently bonded or of a metal complex that can be considered as acting as a single unit in the context of acid and base chemistry or in the formation of salts. The prefix "poly-" means "many," in...

 with the chemical formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 NH. It is formed by the protonation
Protonation
In chemistry, protonation is the addition of a proton to an atom, molecule, or ion. Some classic examples include*the protonation of water by sulfuric acid:*the protonation of isobutene in the formation of a carbocation:2C=CH2 + HBF4 → 3C+ + BF4−*the protonation of ammonia in the...

 of ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

 (NH3). Ammonium is also a general name for positively charged or protonated substituted
Substitution
Substitution may refer to:- Sciences :* Substitution , a syntactic transformation on strings of symbols of a formal language* Substitution of variables* Substitution cipher, a method of encryption...

 amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...

s and quaternary ammonium cation
Quaternary ammonium cation
Quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure NR4+, R being an alkyl group or an aryl group. Unlike the ammonium ion and the primary, secondary, or tertiary ammonium cations, the quaternary ammonium cations are permanently charged,...

s (N+R4), where one or more hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 atoms are replaced by organic radical groups (indicated by R).

In the substitutive nomenclature NH4+ is denoted by the name azanium instead of ammonium.

The ammonium ion is mildly acidic, reacting with Brønsted bases to return to the uncharged ammonia molecule:
NH4+ + :B- → HB + NH3

Thus, treatment of concentrated solutions of ammonium salts with strong base gives ammonia.
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Encyclopedia

The ammonium cation is a positively charged
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...

 polyatomic cation
Polyatomic ion
A polyatomic ion, also known as a molecular ion, is a charged species composed of two or more atoms covalently bonded or of a metal complex that can be considered as acting as a single unit in the context of acid and base chemistry or in the formation of salts. The prefix "poly-" means "many," in...

 with the chemical formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 NH. It is formed by the protonation
Protonation
In chemistry, protonation is the addition of a proton to an atom, molecule, or ion. Some classic examples include*the protonation of water by sulfuric acid:*the protonation of isobutene in the formation of a carbocation:2C=CH2 + HBF4 → 3C+ + BF4−*the protonation of ammonia in the...

 of ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

 (NH3). Ammonium is also a general name for positively charged or protonated substituted
Substitution
Substitution may refer to:- Sciences :* Substitution , a syntactic transformation on strings of symbols of a formal language* Substitution of variables* Substitution cipher, a method of encryption...

 amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...

s and quaternary ammonium cation
Quaternary ammonium cation
Quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure NR4+, R being an alkyl group or an aryl group. Unlike the ammonium ion and the primary, secondary, or tertiary ammonium cations, the quaternary ammonium cations are permanently charged,...

s (N+R4), where one or more hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 atoms are replaced by organic radical groups (indicated by R).

In the substitutive nomenclature NH4+ is denoted by the name azanium instead of ammonium.

Acid-base properties


The ammonium ion is mildly acidic, reacting with Brønsted bases to return to the uncharged ammonia molecule:
NH4+ + :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:
H3O+ + NH3 H2O + NH4+


The degree to which ammonia forms the ammonium ion depends on the pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 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 hydronium ions is low), the equilibrium shifts to the left: the hydroxide
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...

 ion abstracts a proton from the ammonium ion, generating ammonia.

Formation of ammonium compounds can also occur in the vapor
Vapor
A vapor or vapour is a substance in the gas phase at a temperature lower than its critical point....

 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
Solid is one of the three classical states of matter . It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a...

 in a thin white layer on surfaces.

The conversion of ammonium back to ammonia is easily accomplished by the addition of strong base.

Ammonium salts


Ammonium cation is found in a variety of salts such as ammonium carbonate
Ammonium carbonate
Ammonium carbonate is a commercial salt with the chemical formula 2CO3. It is used when crushed as a smelling salt. It can be crushed when needed in order to revive someone who has fainted...

, ammonium chloride
Ammonium chloride
Ammonium chloride NH4Cl is an inorganic compound with the formula NH4Cl. It is a white crystalline salt that is highly soluble in water. Solutions of ammonium chloride are mildly acidic. Sal ammoniac is a name of natural, mineralogical form of ammonium chloride...

, and ammonium nitrate. Most simple ammonium salts are very soluble in water. An exception is ammonium hexachloroplatinate
Ammonium hexachloroplatinate
Ammonium hexachloroplatinate, also known as ammonium chloroplatinate, is a chemical compound with the formula [NH4]2[PtCl6]. It is a rare example of a soluble platinum 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
Perchlorate
Perchlorates are the salts derived from perchloric acid . They occur both naturally and through manufacturing. They have been used as a medicine for more than 50 years to treat thyroid gland disorders. They are used extensively within the pyrotechnics industry, and ammonium perchlorate is also a...

 are highly explosive, in these cases ammonium is the reducing agent.

In an unusual process, ammonium ions form an amalgam
Amalgam (chemistry)
An amalgam is a substance formed by the reaction of mercury with another metal. Almost all metals can form amalgams with mercury, notable exceptions being iron and platinum. Silver-mercury amalgams are important in dentistry, and gold-mercury amalgam is used in the extraction of gold from ore.The...

. Such species are prepared by the electrolysis
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...

 of an ammonium solution using a mercury cathode. This amalgam eventually decomposes to release ammonia and hydrogen.

Structure and bonding


The lone electron pair
Lone pair
In chemistry, a lone pair is a valence electron pair without bonding or sharing with other atoms. They are found in the outermost electron shell of an atom, so lone pairs are a subset of a molecule's valence electrons...

 on the nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 atom (N) in ammonia, represented as a pair of dots, forms the bond with a proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

 (H+). Thereafter, all four N-H bonds are equivalent, being polar covalent bond
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....

s. The ion is isoelectronic
Isoelectronicity
Two or more molecular entities are described as being isoelectronic with each other if they have the same number of electrons or a similar electron configuration and the same structure , regardless of the nature of the elements involved.The term valence isoelectronic is used when these molecular...

 with methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 and borohydride. In terms of size, the ammonium cation (rionic = 175 pm) resembles the caesium
Caesium
Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C , which makes it one of only five elemental metals that are liquid at room temperature...

 cation (rionic = 183 pm).

Organic ammonium ions



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
Dimethylamine
Dimethylamine is an organic compound with the formula 2NH. This secondary amine is a colorless, flammable liquified gas with an ammonia-like odor. Dimethylamine is generally encountered as a solution in water at concentrations up to around 40%...

, (CH3)2NH, and an acid, to give the dimethylaminium cation, (CH3)2NH:


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 surfactant
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...

s.

Biology



Ammonium ions are a waste product of the metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

 of animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...

s. In fish and aquatic invertebrates, it is excreted directly into the water. In mammals, sharks, and amphibians, it is converted in the urea cycle
Urea cycle
The urea cycle is a cycle of biochemical reactions occurring in many animals that produces urea from ammonia . This cycle was the first metabolic cycle discovered , five years before the discovery of the TCA cycle...

 to urea
Urea
Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....

, 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
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 created when the body breaks down purine nucleotides. High blood concentrations of uric acid...

, 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.

Ammonium metal


Ammonium is expected to behave as a metal (NH4+ ions in a sea of electrons) at very high pressures, such as inside gas giant
Gas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...

 planets: see:

See also


  • Ammonium transporter
    Ammonium transporter
    Ammonium transporters are a family of proteins which transport ammonium ions across the cell membrane.-Human proteins containing this domain :RHAG, RHBG, RHCE, RHCG, RHD-Further reading:* [...

  • f-ratio
    F-ratio
    In oceanic biogeochemistry, the f-ratio is the fraction of total primary production fuelled by nitrate . This fraction is significant because it is assumed to be directly related to the sinking flux of organic marine snow from the surface ocean by the biological pump...

  • Hydronium
    Hydronium
    In chemistry, a hydronium ion is the cation , a type of oxonium ion produced by protonation of water. This cation is often used to represent the nature of the proton in aqueous solution, where the proton is highly solvated...

     (H3O+)
  • Iminium
    Iminium
    An iminium salt or cation in organic chemistry has the general structure [R1R2C=NR3R4]+ and is as such a protonated or substituted imine. It is an intermediate in many organic reactions such as the Beckmann rearrangement, Vilsmeier-Haack reaction, Stephen reaction or the Duff reaction...

  • Nitrification
    Nitrification
    Nitrification is the biological oxidation of ammonia with oxygen into nitrite followed by the oxidation of these nitrites into nitrates. Degradation of ammonia to nitrite is usually the rate limiting step of nitrification. Nitrification is an important step in the nitrogen cycle in soil...

  • Onium compounds
    Onium compounds
    Onium compounds are cations derived by the protonation of mononuclear parent hydrides of elements of the nitrogen group , chalcogens , or halogens , and similar cations derived by the substitution of hydrogen atoms in the former by other groups, such as organic radicals, or halogens, for example...