Effective atomic number (EAN) rule: Sidgwick (Z = atomic number, x = oxidation state, n = electrons donated by ligands (2 per simple)
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Z = atomic number, x = oxidation state, n = electrons donated by ligands (2 per simple monodentate L:)
What each symbol means
| Symbol | What it stands for |
|---|---|
| Z | Atomic number of metal |
| n | Number of electrons donated by ligands |
| x | Oxidation state (positive magnitude) |
When to use this
Empirical rule aiming for next noble gas count; works for many carbonyls (e.g. Ni(CO)₄) but many exceptions — JEE tests calculation not universality.