Skip to content
CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Shielding

The partial cancelling of the nuclear charge by the other electrons between a given electron and the nucleus. Core electrons shield valence electrons strongly; electrons in the same shell shield each other very little.

Shielding and effective nuclear charge in sodiumSodium's nucleus has charge +11. Ten core electrons sit between the nucleus and the single 3s valence electron and cancel most of that charge, so the valence electron feels an effective nuclear charge of about +1 (Z − core = 11 − 10).+113s e⁻Na: Z = 1110 core e⁻ shieldZeff ≈ 11 − 10≈ +1shaded core electrons cancel most of the +11

Example

Oxygen's 2p2p electrons are shielded by the two 1s1s core electrons, so they feel Zeff≈8−2=6Z_{\text{eff}} \approx 8 - 2 = 6 rather than the full +8+8.

See alsoEffective nuclear chargeCore electronValence electron