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The combining capacity of an atom or a radical is called its valency. It is measured in terms of hydrogen atoms or oxygen atoms. Valency of an atom or a radical is the number of hydrogen atoms or double the number of oxygen atoms which will combine with it.

Radicals with their valencies and symbols

Basic or Electropositive Radicals

Name Symbol Valency
Aluminium Al 3
Ammonium NH3 1
Antimony Sb 3
Barium Ba 2
Bismuth Bi 3
Cadmium Cd 2
Calcium Ca 2
Chromium Cr 3
Cobalt Co 2
Copper Cu (cuprous) 1
Cu (cupric) 2
Hydrogen H 1
Iron Fe (ferrous) 2
Fe (ferric) 3
Lead Pb (plumbous) 2
Pb (plumbic) 4
Magnesium Mg 2
Manganese Mn (manganous) 2
Mn (manganic) 3
Mercurous 2}} (Mercury I) 2
Mercuric Hg (Mercury II) 2
Nickel Ni 2
Potassium K 1
Silver Ag 1
Sodium Na 1
Strontium Sr 2
Tin Sn (Stannous) 2
Sn (Stannic) 4
Zinc Zn 2

Acid or Electronegative Radicals

Name Symbol Valency
Fluoride F 1
Chloride Cl 1
Hypochlorite ClO 1
Chlorate ClO3 1
Bromide Br 1
Hypobromite BrO 1
Iodide I 1
Sulphide S 2
Sulphite SO3 2
Hypoiodite IO 1
Iodate IO3 1
Bisulphite HSO3 1
Sulphate SO4 2
Bisulphate HSO4 1
Thiosulphate S2O2 2


Nitrate NO3 1
Nitride N 3
Hydroxide OH 1
Oxide O 2
Hydride H 1
Peroxide O2 2
Carbonate CO3 2
Bicarbonate HCO3 1
Carbide C 4
Phosphate PO4 3
Phosphite HPO3 2
Phosphide P 3
Borate BO3 3
Acetate Ch3COO 1
Cyanide CN 1
Manganate MnO4 2
Permanganate MnO4 1
Chromate CrO4 2
Dichromate Cr2O7 2
Ferrocyanide Fe(CN)6 4
Ferricyanide Fe(CN)6 3
Arsenite AsO3 3
Arsenate AsO4 3
Zincate Zn2 2
Meta-Aluminate AlO2 1
Aluminate AlO3 3
Stannate SnO3 2
Silicate SiO3 2

If possible, it is advised to learn the symbols and valencies by heart which can be of great help in studying chemistry further.

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