Anion radius; [tex]r_{a}[/tex] = 0.351 nm
We are given;
Force of attraction: [tex]F_{A}[/tex] = 6.02 × 10⁻⁹ N
Radius of cation; [tex]r_{c}[/tex] = 0.04 nm = 4 × 10⁻¹¹ m
Formula for the force of attraction is given by;
[tex]F_{A}[/tex] = [tex]\frac{1}{4\pi \epsilon_{0} }[/tex] × [tex]\frac{|Z_{1}|*|Z_{2}|*e^{2}}{r^{2}}[/tex]
where;
ε₀ is a constant = 8.85 10⁻¹² N/m
Z₁ is charge on divalent cation = 2
Z₂ is charge on anion = -2
e is charge on an electron = 1.6 × 10⁻¹⁹ C
r = [tex]r_{a}[/tex] + [tex]r_{c}[/tex]
where, [tex]r_{a}[/tex] is radius of anion
Thus;
r = = [tex]r_{a}[/tex] + (4 × 10⁻¹¹) m
Plugging in the relevant values, we have;
6.02 × 10⁻⁹ = [tex]\frac{1}{4\pi * 8.85 * 10^{-12} }[/tex] × [tex]\frac{2 * 2 * (1.6 * 10^{-19})^{2} }{(r_{a} + (4 * 10^{-11})){2} }[/tex]
Simplifying this gives;
[tex]r_{a}[/tex] = 3.51 × 10⁻¹⁰ m = 0.351 nm
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