Question

What is the formula for calcium fluoride? How many fluorine atoms does it contain?

Answer 1

`CaF_2`. Why should this be so? Look at the Periodic Table. Where is calcium? Where is (the element) fluorine.

Explanation:

Calcium is a Group 2 metal. Fluorine is a Group 17 gas. Towards the right of the Periodic table, ELEMENTS tend to get smaller as the increased nuclear charge exerts a greater attractive force on the valence electrons. The small fluorine atom tends to attract electrons, and is energetically most stable when it forms the `F^-` ion.

On the other hand, calcium is a large Group 2 metal. It has 2 valence electrons, which are in the valence (the outermost) shell, and nuclear charge is somewhat diminished for these electrons. Calcium tends to be oxidized (to lose electrons) to form `Ca^(2+)` ions.

So if calcium and fluorine want to make music together (or at least form a chemical bond), then a formula of `CaF_2` is entirely reasonable (why? because this combination is electrically neutral!). And in fact in nature the mineral fluorite (`CaF_2`) is very widespread.