Question

An NaCl molecule is bound due to the electric force between the sodium and the chlorine ions when one electron of sodium is transferred to chlorine. Taking the separation between the ions to be 2.75 × 10⁻⁸ cm, find the force of attraction between them. State the assumptions (if any) that you have made.

Answer 1

Let the given separation between the ions, i.e. 2.75 × 10⁻⁸ cm, be the separation between the transferred electron and the sodium nucleus.

Net charge on thechlorine ion, q₁ = $-1.6\times {10}^{-19}$ C
Net charge on the sodium ion, q₂ = $1.6\times {10}^{-19}$ C
By Coulomb's Law, force,
$F=\frac{1}{4\mathrm{\pi }{\epsilon }_0}\frac{q_1{q}_2}{r^2}$
$$\begin{gathered} =\frac{9\times {10}^9\times {\left(1.6\times {10}^{-19}\right)}^2}{{\left(2.75\times {10}^{-10}\right)}^2} \\ =3.05\times {10}^{-9}\mathrm{N} \end{gathered}$$