6. A student is writing a formula for Magnesium Nitrite. He knows nitrite is a polyatomic ion with a charge of -1. Magnesium is an ion with a charge of +2. He concludes that he will need 2 nitrite ions to balance the charge
across the compound. Thus he writes the final formula as MgN, O2. Explain what he has done wrong.

See explanation

Explanation:

First of all, the student has not represented the formula of the nitrite ion correctly. The formula of the nitrite ion is represented as NO2^- whereas the student wrote N,O2.

Then, the charge on magnesium ion has been correctly designated as +2 while the charge on the nitrite ion is correctly designated as -1. Now, the ions can exchange valencies (without signs and we now write them as subscripts) to yield Mg(NO2)2.