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What is Valency?
Valancy is the combining capacity of an atom. The valency of an element is related to how many electrons are in the orbitals of the outermost shell (also called valence shell).
In other words, the valency of an element is the number of bonds that an atom of the element uses to combine with atoms of other elements to form as part of a compound.
If the number of electrons in the valence shell is less than or equal to 4, then the valency will be the same as the number of electrons present in the valence shell.
For example:- Magnesium (Mg) has atomic number 12. The electronic configuration of magnesium is 2, 8, 2. The number of valence electrons is 2. So the valency is 2.
Carbon (C) has an atomic number 6. The electronic configuration of magnesium is 2, 4. The number of valence electrons is 4. So the valency is 4.
If the number of electrons in the valence shell is more than 4 then the valency will be [8- (the number of valence shell electrons)].
For example:- Phosphorus (P) has atomic number 15. The electronic configuration is 2, 8, 5. So, the valency is (8 - 5) = 3.
Oxygen (O) has an atomic number 8. The electronic configuration is 2, 6. The valency is (8 - 6) = 2.
Elements in the same group of the periodic table have the same valency.
| Group Number | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| Valency | 1 | 2 | 3 | 4 | 3 | 2 | 1 | 0 |
The elements in group number 8 are noble gases, that have the valency 0 because their outermost shell is completely filled which is 8 electrons.
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