Final answer:
To predict the formula of an ionic compound based on the charges of the ions, you need to ensure that the positive and negative charges balance each other out.
Step-by-step explanation:
When predicting the formula of an ionic compound based on the charges of the ions, you need to ensure that the positive and negative charges balance each other out. Start by identifying the charges of the ions involved. The metal ion will have a positive charge, while the nonmetal ion will have a negative charge. For example, in the compound formed between the sodium cation (Na+) and the sulfide anion (S²-), the Na+ ion has a +1 charge and the S²- ion has a -2 charge.
To make the overall compound electrically neutral, the positive and negative charges must cancel each other out. In this case, you would need two Na+ ions (2 x +1 = +2) to balance the charge of one S²- ion (-2). Therefore, the formula of the ionic compound formed is Na₂S.