How to find the valency of molecules like oxide, hydrogen, carbonate?

The valency of a molecule is found by checking how many electrons its atoms need to lose, gain, or share to complete their outer shell.

• Oxide (O²⁻): Oxygen needs 2 electrons, so valency is 2.
• Hydrogen (H⁺): Hydrogen needs 1 electron, so valency is 1.
• Carbonate (CO₃²⁻): The group carries charge –2, so valency is 2.

Steps to find valency:

1. Write the electronic configuration of the atom.
2. See how many electrons it needs to complete its octet (8 electrons).
3. That number is the valency.