Use Lewis symbols to show electron transfer between the following atoms to form cations and anions:
$(a)$ $K$ and $S$
$(b)$ $Ca$ and $O$
$(c)$ $Al$ and $N$

(N/A) $K$ and $S$:
$K$ $([Ar] 4s^1)$ loses one electron to form $K^+$. $S$ $([Ne] 3s^2 3p^4)$ gains two electrons to form $S^{2-}$. Two $K$ atoms transfer electrons to one $S$ atom to form $K_2S$ $(2K^+ + S^{2-})$.
$(b)$ $Ca$ and $O$:
$Ca$ $([Ar] 4s^2)$ loses two electrons to form $Ca^{2+}$. $O$ $([He] 2s^2 2p^4)$ gains two electrons to form $O^{2-}$. They combine to form $CaO$ $(Ca^{2+} + O^{2-})$.
$(c)$ $Al$ and $N$:
$Al$ $([Ne] 3s^2 3p^1)$ loses three electrons to form $Al^{3+}$. $N$ $([He] 2s^2 2p^3)$ gains three electrons to form $N^{3-}$. They combine to form $AlN$ $(Al^{3+} + N^{3-})$.