Effective Nuclear Charge (Z_eff = Z - sigma)
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Z_eff = Z - sigma
What each symbol means
| Symbol | What it stands for |
|---|---|
| Z | Atomic number (nuclear charge in proton units) |
| \sigma | Screening (shielding) constant from inner and same-shell electrons |
| Z_{\mathrm{eff}} | Net positive charge ‘felt’ by a valence electron |
When to use this
Conceptual model for many-electron atoms. σ depends on which electron is considered (different for 3s vs 3p). Used to rationalize periodic trends; not a directly measurable single number for the whole atom.