What is valency

The combining capacity of an element is called its valency. As it can be defined as the number of electrons that an atom may lose or gain during a chemical reaction or the number of electrons shared.

Explanation:

Valency is the combining capacity of an atom—the number of electrons it can lose, gain, or share to form chemical bonds. It helps explain how elements bond, which compounds they form, and why some are more reactive than others.

At the core is the valence shell (the outermost energy level). Atoms tend to achieve a stable (noble-gas-like) configuration, usually by filling or emptying this shell.

How valency relates to the periodic table

• Elements in the same group have the same number of valence electrons, so they often have similar valencies and chemical behavior.
• Typical patterns:
  • 1–4 valence e⁻: often lose/share electrons (e.g., Group 1 metals lose 1).
  • 5–7 valence e⁻: often gain/share electrons (e.g., Group 17 halogens gain 1).
  • 8 valence e⁻ (noble gases): already stable; usually unreactive.

Valency in bonding

• Ionic bonds: electrons are transferred (e.g., Na (valency 1) + Cl (valency 1) → NaCl).
• Covalent bonds: electrons are shared to complete valence shells.

Why valency matters

• Predicts which elements combine and in what ratios.
• Explains reactivity trends (e.g., Group 1 metals are very reactive because they readily lose 1 electron).

In short: Valency links an element’s valence electrons to its bonding behavior, letting us predict compound formation and reactivity across chemistry.