What happens during the formation of an ionic bond in calcium chloride?

Let's first look at the formula for calcium chloride.

It is #CaCl_2#. (Calcium and chlorine)

Now, let's find out its valence electrons.

The number of valence electrons in calcium is 2.
The number of valence electrons in chlorine is 7.

Now remember the Octet Rule : all electrons want to be like noble gases. (That is, with a full outer shell).

The fastest way for chlorine to have a full outer is to get 1 more valence electron.

The fastest way for calcium to have a
full outer shell is to get rid of both of its valence electrons.

Ionic Bonding

But remember, there are #2# chlorine atoms! So overall, they need #2# more electrons to have a full outer shell.

The calcium can supply them with one electron each! Look at how that happens in this diagram.

Since chlorine gained an electron, it is now negatively charged and is called an anion.

On the other hand, calcium gave away two electrons so it is now positively charged. This is called a cation.

Summary

Notice how both these ions have full outer shells.

Unlike in covalent bonding where atoms share valence electrons, in ionic bonding, atoms give electrons.