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đź’ˇ Why atoms bond
Atoms are happiest with a full outer shell (an octet). To get there they lose, gain or share electrons — and that number is the valency.
The outermost shell is the valence shell ; the electrons in it are valence electrons . A full outermost shell of 8 electrons (or 2 for helium) is an octet — such atoms are stable and unreactive.
What is valency?
Valency
The number of electrons an atom gains, loses or shares to complete its octet and become stable. Na equals 1, O equals 2, C equals 4
- The number of electrons an atom gains, loses or shares to complete its octet.
- Fewer than 4 valence electrons → tends to lose (e.g. Na: 2,8,1 → valency 1).
- More than 4 → tends to gain (e.g. O: 2,6 → valency 2).
- Exactly 4 → tends to share (e.g. C: 2,4 → valency 4).
âś… Test Yourself
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What is the valence shell?
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The outermost shell of an atom that contains electrons. -
What is an octet?
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Eight electrons in the outermost shell — a stable arrangement. -
Sodium is 2, 8, 1. What is its valency?
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1 — it loses one electron to get an octet. -
Why is the valency of carbon 4?
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It has 4 valence electrons and shares all four to complete its octet.
Important Definitions
- Valence shell — the outermost shell of an atom that contains electrons.
- Valence electrons — the electrons present in the valence (outermost) shell.
- Octet — a valence shell containing 8 electrons (2 for helium); makes the atom stable and unreactive.
- Valency — the number of electrons gained, lost or shared by an atom to complete its octet.
