= Na+ = Cl-

In the sodium chloride crystal structure, every cation has anions around it, and every anion is surrounded by cations.

Let's look at an animation of the formation of a NaCl crystal.


In the ball and stick model, we observe that each Na+ ion is surrounded by 6 Cl- ions. Similarly, each Cl- ion has 6 Na+ ions as its nearest neighbour.

The electrostatic forces of attraction between ions of opposite charge are the ionic bonds.

 

If we inspect the ball and stick model closely, in a repeating unit of the structure, the ratio of Na+ ion to Cl- ion is 1:1. Therefore, the simplest unit of this ionic compound is NaCl.

In section 5.8, we will look at the rules for writing chemical formulae.