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 C a 2
+ ions. So if calcium and fluorine want to make music together (or at least form a chemical bond), then a formula of (C a F 2) is entirely reasonable (why? because this combination is electrically neutral!). And in fact in nature the mineral fluorite (
C a F
2
) is very widespread.
