The outermost layer of a magnesium ($Mg $) atom has 2 electrons, and the outermost layer of a fluorine ($F $) atom has 7 electrons. When forming magnesium fluoride ($MgF_ {2} $), the magnesium atom loses 2 electrons to form $Mg ^ {2 +} $, and the fluorine atom gains 1 electron to form $F ^ {-} $. Its Lewis point structure is as follows:

$[: F:] ^ {-} Mg ^ {2 +} [: F :]^{-}$

where the small dots around $F $represent its outermost electron, the square brackets represent the ion, and the ionic charge is marked in the upper right corner. The two electrons of the magnesium ion are transferred to the two fluorine atoms, causing the outermost layer of the fluorine atom to reach an 8-electron stable structure, and the magnesium ion also reaches a stable structure.