Skip to content
CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Valence electron

An electron in an atom's outermost shell, the only kind drawn in a Lewis structure. For a main-group atom the count equals the last digit of its group number (group 1 → 1, group 17 → 7).

Nitrogen: 2s2 2p32s^2\,2p^3 gives 5 valence electrons; the 1s21s^2 core is not counted.

Example

POX4X3−\ce{PO4^3-}: 5+4(6)+3=325 + 4(6) + 3 = 32 valence electrons. NOX2X+\ce{NO2+}: 5+2(6)−1=165 + 2(6) - 1 = 16.

See alsoLewis structureOctet ruleCore electron