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 |
| Nitrite |
NO3 |
1 |
| 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.