# Magnitude of Electric Force Between Two Ions

## Homework Statement

Find the magnitude of the electric force between a Na+ ion and a Cl- ion separated by .5 nm.

|F| = (kQq)/r^2

## The Attempt at a Solution

So the problem I am having with this question is this: my first attempt at a solution was to designate |Q| = |q| = 1.6 * 10^-19 C. After which I can just plug these into the equation. But after visiting my professor he told me to multiply Q by 10 (because there are 10 electrons in the Na+ ion) and likewise to multiply q by 18 (because Cl- has 18 electrons). This makes very little sense to me and I hope that someone can help me with this problem. By the way, the answer I originally obtained was 9.23 * 10^-10 N.