# What is an "anion"?

$\text{An ion with a single negative charge...........}$
$\frac{1}{2} {X}_{2} + {e}^{-} \rightarrow {X}^{-}$
Such reduction fills the valence shell of the halide to give an electronic count of $8$; the halide ion, ${X}^{-}$, is reasonably stable.