Q.By using paulings method calculate the ionic radii of K⁺ and Cl⁻ ions in the potassium chloride crystal. Given that d(K⁺-Cl⁻) = 3.14 Å

Step 1. Both K+ (Z=19) and Cl- (Z=17) are isoelectronic with argon, sharing the configuration $1s^2 2s^2 2p^6 3s^2 3p^6$, so both feel the SAME Slater screening constant S for their outer 3p electron.

Step 2. Compute S for a 3p electron in this configuration using Slater's rules: same group (3s,3p) has 7 other electrons x 0.35 = 2.45; one group inward (2s,2p) has 8 electrons x 0.85 = 6.80; two groups inward (1s) has 2 electrons x 1.00 = 2.00. Total $S = 2.45+6.80+2.00 = 11.25$.

Step 3. Effective nuclear charges: $(Z_{eff})_{K^+} = 19 - 11.25 = 7.75$; $(Z_{eff})_{Cl^-} = 17 - 11.25 = 5.75$. …

Compute the shared Slater screening constant once (since both ions are isoelectronic), get each Zeff, form the radius ratio, then …

• Using the atomic number of neutral K or Cl instead of the ION's atomic number (Slater's rule uses the actual Z of the species, but the same electron configuration/count for both, since it is the CONFIGURATION not the original atom that fixes …