What Is Valence or Valency in Chemistry

What Is Valence or Valency in Chemistry

Valency
The combining capacity of an element is known as its valency.
Formulae and valencies of common ions

Electropositive Ions

Monovalent

Bivalent

Name

FormulaNameFormula

Potassium

K+Barium

Ba2+

Sodium

Na+CalciumCa2+
Copper [I]Cu+Magnesium

Mg2+

Manganese [II]

Mn2+
Zinc

Zn2+

Silver

Ag+Iron [II]Fe2+

Ammonium

NH4+

Hydrogen

H+Nickel

Ni2+

Cobalt

Co2+

Tin [II]

Sn2+
Cadmium

Cd2+

Lead [II]

Pb2+
Copper [II]

Cu2+

Trivalent

Tetravalent

Name

FormulaName

Formula

Aluminium

Al3+Manganese [II]

Mn4+

Chromium

Cr3+Tin [IV]

Sn4+

Iron [III]

Fe3+Lead [IV]

Pb4+

Gold

Au3+Platinum

Pt4+

Electropositive Ions
MonovalentBivalent
NameFormulaNameFormula
HydroxideOHCarbonateCO32–
HydrideHChromateCrO42–
FluorideFDichromateCr2O72–
ChlorideClManganateMnO42–
BromideBrTetrathionateS4O62–
IodideISulphideS2–
BicarbonateHCO3SulphiteSO32–
BisulphiteHSO3SulphateSO42–
BisulphateHSO4OxideO2–
ChlorateClO3ZincateZnO22–
HypochloriteClOThiosulphateS2O32–
NitriteNO2
NitrateNO3
PermanganateMnO4
TrivalentTetravalent
NameFormulaNameFormula
NitrideN3–FerrocyanideFe(CN)64–
PhosphatePO43–
FerricyanideFe(CN)63–
PhosphideP3–Pt4+

Variable valency
There are certain elements that exhibit more than one valencies in their ions (or compounds).
Example:       Iron can exist as Fe2+ or Fe3+ in its compounds. In such cases the name of the ion with lower valency ends with a suffix ‘ous’ while that with higher valency ends with a suffix ‘ic’.
Some basic ions exhibiting variable valency

Name of ions

Formula

Cuprous

Cu+

Cupric

Cu2+
Mercurous

Hg22+

Mercuric

Hg2+
Ferrous

Fe2+

Ferric

Fe3+
Plumbous

Pb2+

plumbic

Pb4+
Stannous

Sn2+

Stannic

Sn4+
Aurous

Au+

Auric

Au3+