# Is "Mg"^(2+) a Lewis Acid or Lewis Base?

So, reasonably it should be an electron pair acceptor, and thus a Lewis acid. And while we write $M {g}^{2 +}$, in water we also write $M {g}^{2 +} \left(a q\right)$, by which we mean ${\left[M g {\left(O {H}_{2}\right)}_{6}\right]}^{2 +}$, which is, if you like, a coordination complex of $M {g}^{2 +}$.