Question

Determine the ionic formula for the compound, magnesium oxide.

Answer 1

Hint: Ionic compounds are electrically neutral substances. Magnesium is an S block element, found in the second group of the periodic table. It is an alkaline earth metal. Oxygen, on the other hand, is found in the sixteenth group of the periodic table, and is one of the P block elements. Their respective valencies will determine the ionic formula of the compound.

Complete answer:
Ionic formulas of chemicals are determined by equating the net charge of the compound to zero. Balancing of charges, which the atoms constituting the compound carry, satisfies the neutrality of the compound. Ionic compounds are highly stable in nature.
Magnesium Oxide consists of magnesium and oxygen. Magnesium, being an alkali earth metal, has a valency of $ + 2$ . Magnesium has a tendency of losing two electrons and attaining the stable noble gas configuration. Oxygen, being a part of group sixteen of the periodic table, has a tendency of gaining two electrons and attaining the nearest noble gas configuration. Its valency is $ - 2$ .
 Thus, magnesium and oxygen will exhibit oxidation states of $ + 2$ and $ - 2$ respectively.
In order to neutralize the $ + 2$ valency of magnesium ion, one ion of oxygen of valency $ - 2$ will be required. Hence, the nullification of total charge of the compound is satisfied.
Therefore, the ionic formula for magnesium oxide is $MgO$ .

Note:
Oxygen exhibits $ - 1$ , $ - \dfrac{1}{2}$ and $ + 1$ oxidation states as well, however in most compounds, such as this one, it occurs in $ - 2$ oxidation state. Oxygen exhibits $ - 1$ and $ - \dfrac{1}{2}$ oxidation states when it occurs with alkali metals, the metals belonging to group one of the periodic table. It attains $ + 1$ oxidation state when it forms compounds with fluorine.