Final answer:
The total charge on an ionic compound is neutral, with an equal number of positive and negative charges balancing each other out, as exemplified by the formula Al2O3, which is electrically neutral.
Step-by-step explanation:
The total charge on an ionic compound is always zero because the sum of the positive charges (cations) and the negative charges (anions) must be equal. For example, in the compound aluminum oxide, Al2O3, the two aluminum cations have a charge of +3 each, resulting in a total positive charge of +6. The three oxide anions have a charge of -2 each, leading to a total negative charge of -6. The positive and negative charges balance out, making the compound electrically neutral.
Calculating the charge on monoatomic ions can be done by using the group number in the periodic table. Nonmetals and metalloids form anions with a charge equal to the group number minus eighteen, while metals typically form cations with a positive charge corresponding to their group number.
In summary, when writing the formula of an ionic compound, it is essential to ensure that the number of charges balance so that the total positive charge equals the total negative charge, rendering the compound neutral.