There are three theories that define acids. The Arrhenius theory defines acids as a substance that when added to water the number of H+ ions increases. The Bronsted-Lowry theory defines acids as proton (H⁺) donors, and the Lewis acid-base theory defines acids as electron acceptors. For nomenclature purposes, acids are compounds where the cation is always H⁺, such as HCl or HI.

There are two main types of acids binary acids and oxyacids. Binary acids contain hydrogen and one other element, while oxyacids contain an oxygen atom bonded to a hydrogen atom and at least one other element.

Let’s practice. In the activity below, separate the acids into oxyacids versus binary acids.

Binary acids and oxyacids use different naming systems. In the following sections, you will learn how to name each of these types of acids as well as how to write the formulas for acids when given the name.

In chemistry, it is necessary to have a set of naming rules to distinguish compounds and make sure the same language is spoken in terms of the chemical makeup. Scientists currently follow IUPAC naming rules for nomenclature.