Question

How does calcium obey the octet rule when reacting to form compounds?

Answer 1

It loses two electrons from its outermost shell.

Explanation:

Calcium, `"Ca"`, is located in group 2 of the periodic table, which means that is has two electrons on its outermost shell.

In order to have a complete octet, calcium must lose these two outermost electrons, also called valence electrons.

Calcium will react with nonmetals to form ionic compounds.

The electron configuration for a neutral calcium atom looks like this

`"Ca: " 1s^2 2s^2 2p^6 3s^2 3p^6 color(red)(4)s^2`

After the two outermost electrons are lost, which in a neutral atom occupy the fourth energy level, the calcium cation, `"Ca"^(2+)`, is formed. Its electron configuration looks like this

`"Ca"^(2+): 1s^2 2s^2 2p^6 color(red)(3)s^2 color(red)(3)p^6`

By losing its valence electrons, calcium completes its octet. The outermost shell, which is now the third energy level, holds a total of eight electrons `->` a complete octet

For example, calcium will react with oxygen to form calcium oxide, `"CaO"`. Calcium will donate its two valence electrons to oxygen, forming the `"Ca"^(2+)` cation.

Oxygen will pick up these two electrons, forming the `"O"^(2-)` anion. The resulting compound, `"CaO"`, will thus be electrically neutral.