However, the same element can form more than one acid when compounded with hydrogen and oxygen. In such cases, the English practice to distinguish such acids is to use the suffix "-ic" in the name of the element in the name of the acid containing more oxygen atoms, and the suffix "-ous" in the name of the element in the name of the acid containing fewer oxygen atoms. Thus, for example, sulfuric acid is H2SO4, and sulfurous acid, H2SO3. Analogously, nitric acid is HNO3, and nitrous acid, HNO2. If there are more than two oxyacids having the same element as the central atom, then, in some cases, acids are distinguished by adding the prefix "per-" or "hypo-" to their names. The prefix "per-", however, is used only when the central atom is a halogen or a group 7 element. For example, chlorine has the four following oxyacids: