Question

What is the Lewis Dot Structure for `Mg_2^+`?

Answer 1

If I were to take you literally, it would be a rather unstable cation...

`["Mg"cdots"Mg"]^(+)`
(the dots are an interaction line for a half-bond, not electrons)

Its MO diagram would have one less valence electron than that for `"Mg"_2` (presumed in the gas phase!). This is the MO diagram for the NEUTRAL `"Mg"_2` dimer:

Take one valence electron out of the antibonding `sigma_(3s)^"*"`, and we have a bond order that changed from `1/2(2 - 2) = 0` to `1/2(2 - 1) = 1/2`.

Thus, MO theory suggests that `"Mg"_2^(+)` is more stable than `"Mg"_2`.

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If you mean `"Mg"^(2+)`, it has no valence electrons, so there is not much of a Lewis dot structure to draw... in fact, we have already "drawn" it by writing its chemical symbol and charge.