Valency is the combining capacity of an atom, which determines how many electrons an atom can lose, gain, or share to form a stable bond. It helps in understanding how elements interact to form compounds.

To determine the valency of an element, we look at its valence electrons—the number of electrons present in the outermost shell. If an atom has 1 to 4 valence electrons, its valency is equal to the number of valence electrons. If it has 5 to 8 valence electrons, the valency is calculated as 8 minus the number of valence electrons.

For example, oxygen has 6 valence electrons, so its valency is 8 – 6 = 2, meaning it can form two bonds. Similarly, carbon has 4 valence electrons, so its valency is 4. Sodium has only 1 valence electron, so it readily loses that electron to form a valency of 1.

Here are some common elements and their valency:

• Hydrogen (H) – 1
• Oxygen (O) – 2
• Nitrogen (N) – 3
• Carbon (C) – 4
• Sodium (Na) – 1
• Magnesium (Mg) – 2
• Chlorine (Cl) – 1

Metals generally lose electrons, meaning their valency is equal to the number of electrons lost, while non-metals gain electrons, making their valency (8 – valence electrons). Noble gases like helium, neon, and argon have a complete outer shell, so their valency is zero.

Understanding valency is crucial in chemistry because it helps predict how atoms will bond in molecules, forming compounds that follow stable electron configurations.