What are the formulas of the compounds formed from the following ions? (a) Ca²⁺ and Br^- (b) Ca²⁺ and SO₄^2- (c) Al³⁺ and SO₄^2-

Ionic compounds are formed when cations (positively charged ions) and anions (negatively charged ions) combine. The overall charge of the compound must be neutral, meaning the total positive charge from cations must balance the total negative charge from anions. Understanding how to combine these ions based on their charges is essential for determining the correct formulas of the resulting compounds.

Charge balance is a fundamental principle in chemistry that dictates how ions combine to form neutral compounds. For example, a Ca²⁺ ion has a +2 charge, while a Br^- ion has a -1 charge. To achieve neutrality, two Br^- ions are needed to balance one Ca²⁺ ion, resulting in the formula CaBr₂.

Polyatomic ions are ions composed of two or more atoms that are covalently bonded and carry a net charge. For instance, the sulfate ion (SO₄^2-) has a -2 charge. When combining polyatomic ions with cations, it is crucial to consider the overall charge of the polyatomic ion to ensure the final compound is electrically neutral, as seen in the formation of CaSO₄ and Al₂(SO₄)₃.