Polyatomic Ion

Information about Polyatomic Ion

An electrostatic potential map of the nitrate ion (N O₃⁻). Areas coloured red are lower in energy than areas coloured yellow

A polyatomic ion is a molecule that bears ionic groups, that is, a molecule with a charge. The majority of biological compounds and inorganic species conform to this strict definition. Ordinarily however, the term refers to small collections of atoms, 3 to perhaps 50 atoms, such as many metal complexes and oxyanions such as sulfate. in Greek, the prefix poly- means "many," which to a chemist means three or more atoms.

Hydroxide ions and ammonium ions

A hydroxide ion is made of one oxygen atom and one hydrogen atom: its chemical formula is (O H)⁻. It has a charge of −1.
An ammonium ion is made up of one nitrogen atom and four hydrogen atoms: its chemical formula is (N H₄)⁺. It has charge of +1.

A polyatomic ion can often be considered as the conjugate acid or conjugate base of a neutral molecule. For example the sulfate anion, S O₄²⁻, is derived from H₂SO₄ which can be regarded as SO₃ + H₂O.

There are two "rules" that can be used for the learning the nomenclature of polyatomic ions. First, when the prefix bi- is added to a name, a hydrogen is added to the ion's formula and its charge is increased by 1. It is a consequence of the hydrogen ion carrying a +1 charge. An alternate to the bi- prefix is to use the word hydrogen in its place: the anion derived from H⁺ + CO₃²⁻, HCO₃⁻ can be called either bicarbonate or hydrogencarbonate.

The second rule looks at the number of oxygens in an ion. Consider the chlorine oxoanion family:

oxidation state	−1	+1	+3	+5	+7
anion name	chloride	hypochlorite	chlorite	chlorate	perchlorate
formula	Cl⁻	Cl O⁻	Cl O₂⁻	Cl O₃⁻	Cl O₄⁻
structure

First, think of the -ate ion as being the "base" name, in which case the addition of a per- prefix adds an oxygen. Changing the -ate suffix to -ite will reduce the oxygens by one, and keeping the suffix -ite and adding the prefix hypo- reduces the number of oxygens by two. In all situations, the charge is not affected.

It is important to note that these rules will not work with all polyatomic ions, but they do work with the most common ones (sulfate, phosphate, nitrate, chlorate).

Polyatomic ions vs. radicals

Although most polyatomic ions are diamagnetic (all electrons are paired), some are radicals. Some radicals are charged, and as such are polyatomic ions, such as the radical anion of naphthalene, C₁₀H₈^-. Some can be used in decomposition reactions, providing spectacular results, such as H₂, O₂ and iodine.

List of polyatomic ions

Caution: chemists classify ions and molecules even when such species do not exist to any appreciable extent. For example, small ions with high charges are very rare, as illustrated by the fact that oxide, O^2-, has not been observed in solution and is not considered as a component in reaction mechanisms. Similarly, orthosilicate, SiO₄^4- enjoys no status as an ion in aqueous solution, except perhaps under extreme temperatures. In general, ions that have charges greater than 2- do not exist in solution unless they are protonated.

Polyatomic ions
Acetate	CH₃COO⁻ or C₂H₃O₂⁻
Aluminate	AlO₂⁻, Al₂O₄²⁻
Amide	NH₂⁻
Ammonium	NH₄⁺
Antimonate	SbO₄³⁻
Antimonite	SbO₃³⁻
Arsenate	AsO₄³⁻
Arsenite	AsO₃³⁻
Azide	N₃⁻
Benzoate	C₆H₅COO⁻
Bicarbonate (hydrogen carbonate)	HCO₃⁻
Borate	BO₃³⁻
Metaborate	BO₂⁻
Tetraborate	B₄O₇²⁻
Bromate	BrO₃⁻
Bromite	BrO₂⁻
Carbide	C₂²⁻
Carbonate	CO₃²⁻
Chlorate	ClO₃⁻
Chlorite	ClO₂⁻
Chromate	CrO₄²⁻
Chromite	CrO₂⁻
Chromyl	CrO₂²⁺
Citrate	C₆H₅O₇³⁻
Cyanate	OCN⁻
Cyanide	CN⁻
Dichromate	Cr₂O₇²⁻
Dihydrogen arsenate	H₂AsO₄⁻
Dihydrogen phosphate	H₂PO₄⁻
Dihydrogen phosphite	H₂PO₃⁻
Dioxygenyl	O₂⁺
Disulfide	S₂²⁻
Ferrate	FeO₄²⁻
Ferricyanide	Fe(CN)₆³⁻
Ferrocyanide	Fe(CN)₆⁴⁻
Formate (formiate)	HCO₂⁻
Fulminate	CNO⁻
Hydrazide	N₂H₃⁻
Hydrogen carbonate (bicarbonate)	HCO₃⁻
Hydrogen arsenate	HAsO₄²⁻
Hydrogen phosphate	HPO₄²⁻
Hydrogen phosphite	HPO₃²⁻
Hydrogen sulfate	HSO₄⁻
Hydrogen sulfite	HSO₃⁻
Hydrogen telluride	HTe⁻
Hydronium	H₃O⁺
Hydroxide	OH⁻
Hypobromite	BrO⁻
Hypochlorite	ClO⁻
Hypoiodite	IO⁻
Hypophosphite	PO₂³⁻
Hyposulfite	SO₂²⁻
Periodate	IO₄⁻
Iodate	IO₃⁻
Triiodide	I₃⁻
Iodite	IO₂⁻
Isocyanate	NCO⁻
Mercury(I)	Hg₂²⁺
Manganate	MnO₄²⁻
Molybdate	MoO₄²⁻
Nitrate	NO₃⁻
Nitrite	NO₂⁻
Oxalate	C₂O₄²⁻
Ozonide	O₃⁻
Perbromate	BrO₄⁻
Perchlorate	ClO₄⁻
Permanganate	MnO₄⁻
Peroxide	O₂²⁻
Perrhenate	ReO₄⁻
Peroxomonosulfate	SO₅²⁻
Peroxodisulfate	S₂O₈²⁻
Pertechnetate	TcO₄⁻
Phosphate	PO₄³⁻
Phosphite	PO₃³⁻
Plumbate	PbO₃²⁻
Plumbite	PbO₂²⁻
Pyridinium	C₅H₆N⁺
Pyrophosphate	P₂O₇⁴⁻
Pyrylium	C₅H₅O⁺
Quaternary ammonium	NR₄⁺
Selenate	SeO₄²⁻
Selenite (ion)	SeO₃²⁻
Silicate	SiO₃²⁻
Disilicate	Si₂O₅²⁻
Metasilicate	SiO₃²⁻
Orthosilicate	SiO₄⁴⁻
Pyrosilicate	Si₂O₇⁶⁻
Stannate	SnO₃²⁻
Stannite	SnO₂²⁻
Sulfate	SO₄²⁻
Sulfite	SO₃²⁻
Sulfonium	R₃S⁺
Superoxide	O₂⁻
Tartrate	(CH(OH)COO)₂²⁻
Metatellurate	TeO₄²⁻
Orthotellurate	TeO₆⁶⁻
Tellurite	TeO₃²⁻
Thiocyanate	SCN⁻
Thiosulfate	S₂O₃²⁻
Tosylate (toluenesulfonate)	CH₃C₆H₄SO₃⁻
Triflate (trifluoromethanesulfonate)	CF₃SO₃⁻
Tungstate	WO₄²⁻
Uranyl	UO²⁺
Vanadate	VO₃⁻
Vanadyl	VO²⁺
Pervanadyl	VO₂⁺

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molecule is defined as a sufficiently stable electrically neutral group of at least two atoms in a definite arrangement held together by strong chemical bonds.^[1]^[2] In organic chemistry and biochemistry, the term molecule
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ion is an atom or molecule which has lost or gained one or more electrons, making it positively or negatively charged. A negatively charged ion, which has more electrons in its electron shells than it has protons in its nuclei, is known as an anion
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atom (Greek ἄτομος or átomos meaning "indivisible") is the smallest particle still characterizing a chemical element.
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complex in chemistry usually is used to describe molecules or ensembles formed by the combination of ligands and metal ions. Originally, a complex implied a reversible association of molecules, atoms, or ions through weak chemical bonds.
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An oxyanion or oxoanion is a negatively charged polyatomic ion that contains oxide. Oxyanions can be viewed as the conjugate base of a corresponding oxyacid, although both components are not necessarily stable. Probably the best known oxyanion is DNA.
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In inorganic chemistry, a sulfate (IUPAC-recommended spelling; also sulphate in British English) is a salt of sulfuric acid.

Chemical properties

The sulfate ion is a polyatomic anion with the empirical formula SO₄²⁻
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In chemistry, hydroxide is the most common name for the diatomic anion OH⁻, consisting of oxygen and hydrogen atoms, usually derived from the dissociation of a base. It is one of the simplest diatomic ions known.
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2, −1
(neutral oxide)
Electronegativity 3.44 (Pauling scale)
Ionization energies
(more) 1st: 1313.9 kJmol⁻¹
2nd: 3388.3 kJmol⁻¹
3rd: 5300.5 kJmol⁻¹

Atomic radius 60 pm
Atomic radius (calc.
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1, −1
(amphoteric oxide)
Electronegativity 2.20 (Pauling scale) More

Atomic radius 25 pm
Atomic radius (calc.) 53 pm
Covalent radius 37 pm
Van der Waals radius 120 pm
Miscellaneous

Thermal conductivity (300 K) 180.
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The elementary charge (symbol e or sometimes q) is the electric charge carried by a single proton, or equivalently, the negative of the electric charge carried by a single electron.
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Ammonium is also an old name for the Siwa Oasis in western Egypt.

The ammonium cation is a positively charged polyatomic cation of the chemical formula NH₄⁺. It has a molecular mass of 18.
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3, 5, 4, 2
(strongly acidic oxide)
Electronegativity 3.04 (Pauling scale)
Ionization energies
(more) 1st: 1402.3 kJmol⁻¹
2nd: 2856 kJmol⁻¹
3rd: 4578.1 kJmol⁻¹

Atomic radius 65 pm
Atomic radius (calc.
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conjugate acid is the acid member, HX, of a pair of two compounds that transform into each other by gain or loss of a proton. A conjugate acid can also be seen as the chemical substance that releases a proton in the backward chemical reaction. Thus, the term acid.
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In inorganic chemistry, a sulfate (IUPAC-recommended spelling; also sulphate in British English) is a salt of sulfuric acid.

Chemical properties

The sulfate ion is a polyatomic anion with the empirical formula SO₄²⁻
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6
(strongly acidic oxide)
Electronegativity 2.58 (Pauling scale)
Ionization energies
(more) 1st: 999.6 kJmol⁻¹
2nd: 2252 kJmol⁻¹
3rd: 3357 kJmol⁻¹

Atomic radius 100 pm
Atomic radius (calc.
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Sulfuric (or sulphuric) acid, H₂SO₄, is a strong mineral acid. It is soluble in water at all concentrations. It was once known as oil of vitriol, coined by the 8th-century Arabian alchemist Jabir ibn Hayyan (Geber) after his discovery of the chemical.
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Sulfur trioxide (also spelled sulphur trioxide) is the chemical compound with the formula SO₃. In the gaseous form, this species is an important pollutant, being the primary agent in acid rain. It is prepared on massive scale as a precursor to sulfuric acid.
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Water is a common chemical substance that is essential to all known forms of life.^[1] In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor.
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carbonate is a salt or ester of carbonic acid.

Applications

Soda water (also known as Seltzer water) is water with CO₂ dissolved under pressure. The taste of soda water was discovered by the 18th century chemist Joseph Priestley.
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bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid.

Chemical properties

The bicarbonate ion (hydrogen carbonate) is an anion with the empirical formula HCO₃
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1, 3, 5, 7
(strongly acidic oxide)
Electronegativity 3.16 (Pauling scale)
Ionization energies
(more) 1st: 1251.2 kJmol⁻¹
2nd: 2298 kJmol⁻¹
3rd: 3822 kJmol⁻¹

Atomic radius 100 pm
Atomic radius (calc.
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The chloride ion is formed when the element chlorine picks up one electron to form an anion (negatively-charged ion) Cl ⁻ . The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides.
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The chlorite(I) ion is ClO⁻. A chlorite(I) compound is a chemical compound containing this group, with chlorine in oxidation state +1.

Chlorites(I) are the salts of hypochlorous acid.
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Chlorite is also a type of mineral; see chlorite group.

The chlorite ion is ClO₂⁻. A chlorite (compound) is a compound that contains this group, with chlorine in oxidation state +3.
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The chlorate ion ClO₃⁻.

A chlorate (compound) is a compound that contains this group, with chlorine in oxidation state +5.

Examples

ClO₃⁻ has a trigonal pyramidal structure.
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Perchlorates are the salts derived from perchloric acid (HClO₄). They occur both naturally and through manufacturing. They have been used as a medicine for more than 50 years to treat thyroid gland disorders.
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Polyatomic Ion

Information about Polyatomic Ion

Polyatomic ions vs. radicals

List of polyatomic ions

See also

External links

Chemical properties

Chemical properties

Applications

Chemical properties

Examples