Science, Tech, Math › Science How to Name Ionic Compounds Ionic Compound Nomenclature Explained Share Flipboard Email Print Hero Images / Getty Images Science Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated May 11, 2019 Ionic compounds consist of cations (positive ions) and anions (negative ions). Ionic compound nomenclature or naming is based on the names of the component ions. In all cases, ionic compound naming gives the positively charged cation first, followed by the negatively charged anion. Here are the principal naming conventions for ionic compounds, along with examples to show how they are used: Roman Numerals in Ionic Compound Names A Roman numeral in parentheses, followed by the name of the element, is used for elements that can form more than one positive ion. There is no space between the element name and the parenthesis. This notation is usually seen with metals since they commonly display more than one oxidation state or valence. You can use a chart to see the possible valences for the elements. Fe2+ Iron(II)Fe3+ Iron(III)Cu+ Copper(I)Cu2+ Copper(II) Example: Fe2O3 is iron(III) oxide. Naming Ionic Compounds Using -ous and -ic Although Roman numerals are used to denote the ionic charge of cations, it is still common to see and use the endings -ous or -ic. These endings are added to the Latin name of the element (e.g., stannous/stannic for tin) to represent the ions with lesser or greater charge, respectively. The Roman numeral naming convention has wider appeal because many ions have more than two valences. Fe2+ FerrousFe3+ FerricCu+ CuprousCu2+ Cupric Example: FeCl3 is ferric chloride or iron(III) chloride. Naming Ionic Compounds Using -ide The -ide ending is added to the name of a monoatomic ion of an element. H- HydrideF- FluorideO2- OxideS2- SulfideN3- NitrideP3- Phosphide Example: Cu3P is copper phosphide or copper(I) phosphide. Naming Ionic Compounds Using -ite and -ate Some polyatomic anions contain oxygen. These anions are called oxyanions. When an element forms two oxyanions, the one with less oxygen is given a name ending in -ite and the one with more oxygen are given a name that ends in -ate. NO2- NitriteNO3- NitrateSO32- SulfiteSO42- Sulfate Example: KNO2 is potassium nitrite, while KNO3 is potassium nitrate. Naming Ionic Compounds Using hypo- and per- In the case where there is a series of four oxyanions, the hypo- and per- prefixes are used in conjunction with the -ite and -ate suffixes. The hypo- and per- prefixes indicate less oxygen and more oxygen, respectively. ClO- HypochloriteClO2- ChloriteClO3- ChlorateClO4- Perchlorate Example: The bleaching agent sodium hypochlorite is NaClO. It is also sometimes called the sodium salt of hypochlorous acid. Ionic Compounds Containing bi- and di- Hydrogen Polyatomic anions sometimes gain one or more H+ ions to form anions of a lower charge. These ions are named by adding the word hydrogen or dihydrogen in front of the name of the anion. It is still common to see and use the older naming convention in which the prefix bi- is used to indicate the addition of a single hydrogen ion. HCO3- Hydrogen carbonate or bicarbonateHSO4- Hydrogen sulfate or bisulfateH2PO4- Dihydrogen phosphate Example: The classic example is the chemical name for water, H2O, which is dihydrogen monoxide or dihydrogen oxide. Dihydrogen dioxide, H2O2, is more commonly called hydrogen dioxide or hydrogen peroxide.