Skip to content

List of Polyatomic Ions and Charges

 Simple ions – The ions which are formed from single atom carrying a positive or negative charge are called simple ions or mono-atomic ions.
Example – Na+, Cl, O-2, Al+3, N-3(nitride), Mg+2, Ca+2, Cu+2, Fe+2etc.

Polyatomic ions
-Polyatomic ions or compound ions are molecules formed from groups of atoms bonded together that carry a positive or negative charge.
Example – NH4+, CO3-2, OH, SO4-2, NO3, PO4-3, SO3-2   etc.

Read first–

Ions – Anions and Cations

Common Simple and Polyatomic Ions –


CO3-2           carbonate
HCO3          hydrogen carbonate / (bicarbonate)


NO3             nitrate
NO2             nitrite
N-3                nitride
NH4+             ammonium


SO42-            sulphate
SO32-            sulphite
S2O32-          thiosulphate
HSO4           hydrogen sulphate  / (bisulphate)
HSO3           hydrogen sulphite / (bisulphite)
S2-                sulphide


ClO4           perchlorate
ClO3           chlorate
ClO2           chlorite
ClO             hypochlorite

PO43-           phosphate
HPO42-        hydrogen phosphate
H2PO4        dihydrogen phosphate

CN             cyanide        
OH             hydroxide
Cl               chloride
F                 fluoride
Br               bromide
I                 iodide
H                   hydride
H+               hydrogen
Na+            sodium
K+               potassium
Ag+             silver
Cu+             copper(I)
Mg+2          magnesium
Ca+2           calcium
O-2             oxide
Zn+2           zinc
Cu+2          copper(II)
Fe+2           iron (II)
Al+3           aluminium
Fe+3           iron (III)

Some elements show more than one valency. A roman numeral shows their valency in the bracket.

Don’t Miss –

Problems based on law of definite proportions or constant composition
How to write chemical formula of a simple Compound 
How do you write Chemical Formula for an ionic Compound?

Common naming practices 

If you can remember the formula of the ion whose name ends with ate, you can usually work out the formulas of the other family members as follows-
Stem name      Meaning                      
-ate             a common form, containing oxygen
Examples      –
chlorate    –      ClO3
nitrate       –      NO3
sulphate    –      SO4-2
carbonate  –      CO3-2

Stem name      Meaning
-ite                   one less oxygen  than -ate form
Examples      –
chlorite     –   ClO2
sulphite    –   SO32-
nitrite       –    NO2

Stem name      Meaning
per-, -ate
          same charge, but contains one more oxygen
than -ate form   
 Examples      –
perchlorate     –    ClO4
perbromate    –    BrO4–                         

Stem name      Meaning
hypo-, -ite         same charge, but contains one less oxygen
than -ite form
 Examples      –
hypochlorite    –    ClO
hypobromite   –    BrO

Stem name      Meaning
thio-                 replace an O with an S
Examples      –
thiosulphate     –    S2O32-
thiosulphite      –    S2O22-

Some anions can capture hydrogen ions. For example, carbonate (CO3-2 ) can capture an H+ to produce hydrogen carbonate ( HCO3  often called bicarbonate). Each captured hydrogen neutralizes one minus charge on the anion.

Stem name                 Meaning 
hydrogen or bi-
           captured H+ ions

hydrogen carbonate or bicarbonate   –   HCO3
hydrogen sulphate or bisulphate        –   HSO4

Stem name               Meaning
dihydrogen               captured 2H+ ions
dihydrogen phosphate   –   H2PO4

Read  also –

Law of Conservation of Mass
Problems based on Law of Conservation of Mass
Law of Definite Proportions / Constant Composition

  •  Radicals –  An atom or group of atoms that contains one or more unpaired electrons (usually very reactive species).  It can also be defined as a single atom or a group of atoms that behaves as a single unit and possess an electric charge.

Next –