- 2071 Bhadra · 1+4 marks
Effective atomic number and IUPAC names
Short answer
Effective atomic number (EAN) = (Z – oxidation state) + 2×coordination number. IUPAC: [Fe(CN)6]3- hexacyanoferrate(III) ion, EAN=35; [Ag(NH3)4]+ tetraamminesilver(I) ion, EAN=54; [Ni(CN)4]2- tetracyanonickelate(II) ion, EAN=34; [Cr(H2O)6]3+ hexaaquachromium(III) ion, EAN=33.
What do you mean by effective atomic number? Give IUPAC name and calculate the effective atomic number of the following complexes. a) [Fe(CN)₆]³⁻ b) [Ag(NH₃)₄]⁺ c) [Ni(CN)₄]²⁻ d) [Cr(H₂O)₆]³⁺
Effective atomic number (EAN)
The EAN is the total number of electrons around the central metal atom/ion in a complex, counting the electrons gained by coordination. EAN = (Z − oxidation state) + 2 × (number of ligands). Stable complexes often have EAN equal to the next noble gas (Sidgwick's rule).
| Complex | IUPAC name | Z | Ox. state | Calculation | EAN |
|---|---|---|---|---|---|
| [Fe(CN)₆]³⁻ | hexacyanoferrate(III) ion | 26 | +3 | 26 − 3 + 12 | 35 |
| [Ag(NH₃)₄]⁺ | tetraamminesilver(I) ion | 47 | +1 | 47 − 1 + 8 | 54 |
| [Ni(CN)₄]²⁻ | tetracyanonickelate(II) ion | 28 | +2 | 28 − 2 + 8 | 34 |
| [Cr(H₂O)₆]³⁺ | hexaaquachromium(III) ion | 24 | +3 | 24 − 3 + 12 | 33 |
Answer: EAN = 35, 54, 34 and 33 respectively. (Kr = 36 and Xe = 54, so only the silver complex reaches a noble gas value.)
✓ Answer checked by Claude Opus 5.5 (high effort)
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