IUPAC Name and Formula of Anions Introductory Chemistry Tutorial

Key Concepts

An anion is a negatively charged ion.

An anion can be composed of:
⚛ one atom (monoatamic anion)

⚛ more than one atom (polyatomic anion)

The formula of a monoatomic⁽¹⁾ anion is made up of two parts:

Formula of Monoatomic Anion

symbol of element charge as a superscript⁽²⁾ to the right of the symbol

E ^x-

Note the charge on the anion is given with the number first followed by the minus sign.

E^x- NOT E^-x

Formula of Monoatomic Anion
symbol of element	charge as a superscript⁽²⁾ to the right of the symbol
E	^x-

The charge on a monoatomic anion of a non-metal element can be determined from its location in the periodic table of the elements.

The table below gives the symbol of non-metal elements and the charge of the respective anions:

	Group 14	Group 15 (pnictogens)	Group 16 (chalcogens)	Group 17 (halogens)
	Groups of the Periodic Table
Period 2	C 4-	N 3-	O 2-	F 1-
Period 3		P 3-	S 2-	Cl 1-
Period 4			Se 2-	Br 1-
Period 5				I 1-
Charge on Anions in Group	4-	3-	2-	1-

Hydrogen (H), period 1, can also form an anion with a charge of 1-

The name of a monoatamic anion is made up of three parts:
(i) modified name of the element

(ii) "ide" substituted for the end of the name

(iii) charge on the anion given in parentheses (x-)

Acceptable IUPAC Name
of Monoatomic Anion

prefix ide (charge on anion)

modified name of element ide (x-)

Note there is no space between the modified name of the element and the "ide" suffix nor is there a space between the "ide" and the parentheses enclosing the charge on the anion:

elemide(x-) NOT elem ide(x-) NOT elemide (x-)

Note that the charge in parentheses (x-) may be omitted if there is no ambiguity in the name.

Acceptable IUPAC Name of Monoatomic Anion
prefix	ide	(charge on anion)
modified name of element	ide	(x-)

The name of the element present in the anion is modified by removing the end of the element's name.

Examples of the ends of non-metal element names that get removed are:

removable ending	Non-metal Examples
removable ending	Element Name	Modified Name
ine	fluorine	fluor
	chlorine	chlor
	bromine	brom
	iodine	iod
ium	selenium	selen
ogen	hydrogen	hydr
ogen	nitrogen	nitr
on	carbon	carb
orus	phosphorus	phosph
ur	sulfur	sulf
ygen	oxygen	ox

You may be expected to know the name and formula of some polyatomic anions⁽³⁾, especially those derived from inorganic acids, as shown in the table below:

Inorganic Acid		Polyatomic Anions Derived from Acid
Acceptable Name ⁽⁴⁾	Formula	Acceptable Name ⁽⁵⁾	Formula
nitric acid	HNO₃	nitrate	NO₃^-
nitrous acid	HNO₂	nitrite	NO₂^-
carbonic acid	H₂CO₃	hydrogencarbonate	HCO₃^-
carbonic acid	H₂CO₃	carbonate	CO₃^2-
sulfuric acid	H₂SO₄	hydrogensulfate	HSO₄^-
sulfuric acid	H₂SO₄	sulfate	SO₄^2-
sulfurous acid	H₂SO₃	hydrogensulfite	HSO₃^-
sulfurous acid	H₂SO₃	sulfite	SO₃^2-
phosphoric acid	H₃PO₄	dihydrogenphosphate	H₂PO₄^-
		hydrogenphosphate	HPO₄^2-
		phosphate	PO₄^3-
phosphorous acid	H₃PO₃	dihydrogenphosphite	H₂PO₃^-
		hydrogenphosphite	HPO₃^2-
		phosphite	PO₃^3-
perchloric acid	HClO₄	perchlorate	ClO₄^-
chloric acid	HClO₃	chlorate	ClO₃^-
chlorous acid	HClO₂	chlorite	ClO₂^-
hypochlorous acid	HClO	hypochlorite	OCl^-

Note that in the accepted abbreviated "hydrogen names"⁽⁶⁾ of anions there is no space between the word "hydrogen" and the rest of the name:

hydrogencarbonate NOT hydrogen carbonate

You may be expected to know the name and formula of this polyatomic anion derived from an inorganic base ⁽⁷⁾:
hydroxide : OH^-

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Writing the Formula of a Monoatomic Anion Using Its Name

The name of a monoatamic anion is made up of three parts:

(i) name of the element with ending removed

(ii) "ide" substituted for the end of the element's name

(iii) charge on the anion enclosed in parentheses (may be omitted if there is no ambiguity in the name)

We use this information in the name to help us write the formula of the anion as shown in the steps below:

Break the name of the monoatomic anion up into its three parts:

name of element with ending removed ide (charge in parentheses )

Use the periodic table of the elements to find the symbol for the name of the element (remember that the end of the element's name has been removed in the name of the anion!)

name of element with ending removed ide (charge in parentheses )

E

Determine the charge on the monoatomic anion based on either of the two methods below:
(i) charge enclosed in parentheses (x-)

(ii) its location in the periodic table

The charge is written with the number first followed by the minus sign.

name of element with ending removed ide (charge in parentheses )

E x-

Write the formula in the format of symbol of the element with the charge given as superscript to the right of the symbol.
Note: if the charge is 1- we do not need to write the "1", we just write the minus sign, -

E^x-

Worked Examples: Writing the Formula of a Monoatomic Anion

Question 1: Write the formula for the anion with the name chloride(1-) or chloride

Solution:

Break the name of the monoatomic anion up into its three parts:

modified name ide (charge in parentheses )

chlor ide (1-)

Use the periodic table of the elements to find the symbol for the name of the element (remember that the end of the element's name has been removed in the name of the anion!)

chlor~~ine~~ ide (1-)

Cl

Determine the charge on the monoatomic anion based on its location in the periodic table
(i) charge enclosed in parentheses : (1-)

(ii) its location in the periodic table: all Group 17 elements can form an anion with charge 1-

The charge is written with the number first followed by the minus sign.

chlor~~ine~~ ide (1-)

Cl 1-

Write the formula in the format of symbol of the element with the charge given as superscript to the right of the symbol.
The charge is 1- we DO NOT write the "1", we just write the minus sign, -

Cl^-

Question 2: Write the formula for the anion with the name sulfide

Solution:

Break the name of the monoatomic anion up into its three parts:

modified name ide (charge in parentheses )

sulf ide

Use the periodic table of the elements to find the symbol for the name of the element (remember that the end of the element's name has been removed in the name of the anion!)

sulfur ide (charge not given)

S

Determine the charge on the monoatomic anion based on its location in the periodic table
(i) charge enclosed in parentheses : has been omitted from name

(ii) its location in the periodic table: all Group 16 non-metal elements can form an anion with charge 2-

The charge is written with the number first followed by the minus sign.

sulfur ide (charge from location in periodic table)

S 2-

Write the formula in the format of symbol of the element with the charge given as superscript to the right of the symbol.
The charge is NOT 1- we DO need write the "2" to the left of the minus sign, -

S^2-

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Naming a Monoatomic Anion Using Its Formula

The formula of a monoatomic anion is made up of two parts:

symbol of the element

charge on the anion as a superscript number to the right of the symbol

We use this information in the formula to help us name the monoatomic anion as shown below:

Break the formula up into its two parts:

symbol of element charge as a superscript to the right of the symbol

E ^x-

Use the periodic table of the elements to find the name for the element with this symbol:

E ^x-

namine

Modify the element's name by removing the end of the name (ine, ium, ogen, on, orus, ur, ygen)

E ^x-

nam~~ine~~

Add the suffix "ide" to the modified name of the element:

E ^x-

namide

Enclose the charge on the anion in parentheses
Note if the charge on the anion is -, then the charge enclosed in parentheses will be 1-

E ^x-

namide (x-)

Assemble the name as one word, no space between the modified name of the element and the "ide" suffix, no space between the "ide" and the charge enclosed in parentheses .
Note that the charge in parentheses may by omitted if there will be no ambiguity in the name.

namide(x-)

Worked Examples: Naming a Monoatomic Anion

Question 1: Name the anion that has the formula F^-

Solution:

Break the formula up into its two parts:

symbol of element charge as a superscript to the right of the symbol

F ^-

Use the periodic table of the elements to find the name for the element with this symbol:

F ^-

fluorine

Modify the element's name by removing the end of the name (ine, ium, ogen, on, orus, ur, ygen)

F ^-

fluor~~ine~~

Add the suffix "ide" to the modified name of the element:

F ^-

fluoride

Enclose the charge on the anion in parentheses
Note that the charge on this anion is -, so the charge enclosed in parentheses will be 1-

F ^-

fluoride (1-)

Assemble the name as one word, no space between the modified name of the element and the "ide" suffix, no space between the "ide" and the charge enclosed in parentheses .
fluoride(1-)

Note that the charge in parentheses may by omitted if there will be no ambiguity in the name.

fluoride

Question 2: Name the anion that has the formula O^2-

Solution:

Break the formula up into its two parts:

symbol of element charge as a superscript to the right of the symbol

O ^2-

Use the periodic table of the elements to find the name for the element with this symbol:

O ^2-

oxygen

Modify the element's name by removing the end of the name (ine, ium, ogen, on, orus, ur, ygen)

O ^2-

ox~~ygen~~

Add the suffix "ide" to the modified name of the element:

O ^2-

oxide

Enclose the charge on the anion in parentheses
Note that the charge on this anion is 2-, so the charge enclosed in parentheses will be 2-

O ^2-

oxide (2-)

Assemble the name as one word, no space between the modified name of the element and the "ide" suffix, no space between the "ide" and the charge enclosed in parentheses .
oxide(2-)

Note that the charge in parentheses may by omitted if there will be no ambiguity in the name.

oxide

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Footnotes: reference "Nomenclature of Inorganic Chemistry: IUPAC Recommendations 2005" (Red Book)

(1) monoatomic or monotomic or monatomic? The IUPAC document cited above uses monoatomic so we will too!

(2) This location around the symbol of an element is actually referred to as the "right upper index".

left upper index	symbol	right upper index
left lower index	symbol	right lower index

(3) Note that the naming of complex anions will not be covered in this tutorial.
See the Ligands and Complex Ions tutorial for more information.

(4) IUPAC considers these names as acceptable but it should be noted that these names do not follow stoichiometric, substitutive or additive nomenclature rules.
Acceptable formula are give in the classical oxoacid format with the "acid" (oxygen-bound) hydrogens listed first, followed by the central atom then the oxygen atoms.
The corresponding formula written as coordination entities and systematic IUPAC additive names of these inorganic acids are given below:
nitric acid: [NO₂(OH)] hydroxidodioxidonitrogen
nitrous acid: [NO(OH)] hydroxidooxidonitrogen
carbonic acid: [CO(OH₂] dihydroxidooxidocarbon
sulfuric acid: [SO₂(OH)₂] dihydroxidodioxidosulfur
sulfurous acid: [SO(OH)₂] dihydroxidooxidosulfur
phosphoric acid: [PO(OH)₃] trihydroxidooxidophosphorus
phosphorous acid: [P(OH)₃] trihydroxidophosphorus
perchloric acid: [ClO₃(OH)] hydroxidotrioxidochlorine
chloric acid: [ClO₂(OH)] hydroxidodioxidochlorine
chlorous acid: [ClO(OH)] hydroxidooxidochlorine
hypochlorous acid:[O(H)Cl] chloridohydridooxygen

(5) IUPAC considers these names as acceptable but it should be noted that these names do not follow stoichiometric, substitutive or additive nomenclature rules.
The corresponding formula written as coordination entities and systematic IUPAC additive names of these anions are given below:
nitrate: [NO₃]^- trioxidonitrate(1-)
nitrite: [NO₂]^- dioxidonitrate(1-)
hydrogencarbonate: [CO₂(OH)]^- hydroxidodioxidocarbonate(1-)
carbonate: [CO₃]^2- trioxidocarbonate(2-)
hydrogensulfate: [SO₃(OH)]^- hydroxidotrioxidosulfate(1-)
sulfate: [SO₄]^2- tetraoxidosulfate(2-)
hydrogensulfite: [SO₂(OH)]^- hydroxidodioxidosulfate(1-)
sulfite: [SO₃]^2- trioxidosulfate(2-)
dihydrogenphosphate: [PO₂(OH)₂]^- dihydroxidodioxidophosphate(1-)
hydrogenphosphate: [PO₃(OH)]^2- hydroxidotrioxidophosphate(2-)
phosphate: [PO₄]^3- tetraoxidophosphate(3-)
dihydrogenphosphite: [PO(OH)₂]^- dihydroxidooxidophosphate(1-)
hydrogenphosphite: [PO₂(OH)]^2- hydroxidodioxidophosphate(2-)
phosphite: [PO₃]^3- trioxidophosphate(3-)
perchlorate: [ClO₄]^- tetraoxidochlorate(1-)
chlorate: [ClO₃]^- trioxidochlorate(1-)
chlorite: [ClO₂]^- dioxidochlorate(1-)
hypochlorite:[OCl]^- chloridooxygenate(1-)

(6) "Hydrogen name" can be used when one or more hydrons (protons) are attached to an anion at:

an unknown position
a position you don't want to specifiy

"Hydrogen names" are commonly used for simpler compounds such as the partially dehydronated (deprotonated) oxoacids listed here.
The hydrogen names listed on the page above are the IUPAC accepted abbreviated names.
The IUPAC rules for writing a hydrogen name:

"hydrogen" MUST be attached to the rest of the name (no space between "hydrogen" and the rest of the name
number of hydrogens MUST be specified by a multiplicative prefix eg, (di=2, tri=3, tetra=4)
the anionic part of name MUST be placed in enclosing remarks eg, (anion name)
the charge of the TOTAL structure being named is specified, eg charge of 1- (1-), charge of 2- (2-) etc

The list below gives the "hydrogen name" and the abbreviated hydrogen name for anions as accepted by IUPAC:
HCO₃^-: hydrogen(trioxidocarbonate(1-) abbreviated as hydrogencarbonate
HSO₄^-: hydrogen(tetraoxidosulfate)(1-) abbreviated as hydrogensulfate
HSO₃^-: hydrogen(trioxidosulfate)(1-) abbreviated as hydrogensulfite
H₂PO₄^-: dihydrogen(tetraoxidophosphate)(1-) abbreviated as dihydrogenphosphate
HPO₄^2-: hydrogen(tetraoxidophosphate)(2-) abbreviated as hydrogenphosphate
H₂PO₃^-: dihydrogen(trioxidophosphate)(1-) abbreviated as dihydrogenphosphite
HPO₃^2-: hydrogen(trioxidophosphate)(2-) abbreviated as hydrogenphosphite

(7) To be consistent with the rules for the construction of a formula (order of increasing electronegativity, that is symbol for least electronegative atom written first, symbol for most electronegative element written last), hydroxide should be given the formula HO^- NOT OH^-. However, the formula OH^- for hydroxide is well established and accepted.
Systematic IUPAC names for hydroxide are:

oxidanide (substitutive name : water, H₂O, named as oxidane, negative ion produced by dehydronation (deprotonation) is HO^- hence named as oxidanide)
hydridooxygenate(1-) (additive name)

name of element with ending removed	ide	(charge in parentheses )
E

symbol of element	charge as a superscript to the right of the symbol
E	^x-

chlor~~ine~~	ide	(1-)
Cl

chlor~~ine~~	ide	(1-)
Cl		1-

E	^x-
namine

E	^x-
nam~~ine~~