What is the ionic formula for magnesium oxide?
The ionic formula for magnesium oxide is MgO.
Why is this the case?
The Magnesium ion is an Alkaline Earth Metal and wants to give up the 2 s orbital elections and become a +2 cation.
Oxygen has six valence electrons and is looking to gain two electrons to complete the octet (8) electron count in the valence shell making it a -2 anion.
When the charges of the Magnesium +2 and the Oxygen -2 are equal and opposite, the ions for an electrical attraction. (Remember Paula Abdul told us "Opposites Attract")
This one to one ratio of charges makes the formula MgO.