Valency is the combining capacity of an element — the number of electrons it can gain, lose, or share to form a chemical bond and achieve a stable noble gas configuration. Learning the valency of common elements is essential for writing chemical formulas correctly.
Elements like Iron (Fe), Copper (Cu), and Mercury (Hg) show variable valency. Iron can be +2 (ferrous) or +3 (ferric). This is why it forms two different types of oxides: FeO and Fe₂O₃.
Elements belonging to the same group in the Periodic Table have the same valency. This is one of the most important patterns in chemistry.
| Element | Symbol | Atomic No. | Valency |
|---|---|---|---|
| Hydrogen | H | 1 | 1 |
| Helium | He | 2 | 0 |
| Lithium | Li | 3 | 1 |
| Carbon | C | 6 | 4 |
| Nitrogen | N | 7 | 3 |
| Oxygen | O | 8 | 2 |
| Sodium | Na | 11 | 1 |
| Magnesium | Mg | 12 | 2 |
| Aluminium | Al | 13 | 3 |
| Silicon | Si | 14 | 4 |
| Sulphur | S | 16 | 2 |
| Chlorine | Cl | 17 | 1 |
| Potassium | K | 19 | 1 |
| Calcium | Ca | 20 | 2 |
| Iron | Fe | 26 | 2, 3 |
| Copper | Cu | 29 | 1, 2 |
| Zinc | Zn | 30 | 2 |
| Silver | Ag | 47 | 1 |
| Gold | Au | 79 | 1, 3 |
Count the electrons in the outermost shell. If the outer shell has 1-4 electrons, that number is usually the valency. If it has 5-8 electrons, the valency is usually (8 minus the number of outer electrons). For example, Oxygen has 6 outer electrons: 8 - 6 = valency 2.
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