Q.Explain the pauling method for the determination of ionic radius.

Step 1. Pauling assumed the cation and anion in a uni-univalent ionic crystal are perfect spheres in contact, so the experimentally measured inter-ionic distance is their sum: $d = r_{C^+} + r_{A^-}$.

Step 2. For ions sharing a noble-gas electron configuration, he further assumed radius is inversely proportional to the effective nuclear charge felt at the ion's periphery: $r_{C^+} \propto 1/(Z_{eff})_{C^+}$ and $r_{A^-} \propto 1/(Z_{eff})_{A^-}$.

Step 3. Dividing these two proportionalities gives the RATIO of the two radii purely from their Slater effective nuclear charges: $r_{C^+}/r_{A^-} = (Z_{eff})_{A^-}/(Z_{eff})_{C^+}$. …

Present both of Pauling's assumptions (touching spheres; radius inversely proportional to Zeff) and show …

• Stating only 'd = rC+ + rA-' without explaining how the SPLIT between the two radii is ac …