Skills to Develop Derive names for common types of inorganic compounds using a systematic approach Nomenclature , a collection of rules for naming things, is important in science and in many other situations. This module describes an approach that is used to name simple ionic and molecular compounds, such as NaCl, CaCO 3 , and N 2 O 4 . The simplest of these are binary compounds , those containing only two elements, but we will also consider how to name ionic compounds containing polyatomic ions, and one specific, very important class of compounds known as acids (subsequent chapters in this text will focus on these compounds in great detail). We will limit our attention here to inorganic compounds, compounds that are composed principally of elements other than carbon, and will follow the nomenclature guidelines proposed by IUPAC. The rules for organic compounds, in which carbon is the principle element, will be treated in a later chapter on organic chemistry. Ionic Compounds To name an inorganic compound, we need to consider the answers to several questions. First, is the compound ionic or molecular? If the compound is ionic, does the metal form ions of only one type (fixed charge) or more than one type (variable charge)? Are the ions monatomic or polyatomic? If the compound is molecular, does it contain hydrogen? If so, does it also contain oxygen? From the answers we derive, we place the compound in an appropriate category and then name it accordingly. Compounds Containing Only Monatomic Ions The name of a binary compound containing monatomic ions consists of the name of the cation (the name of the metal) followed by the name of the anion (the name of the nonmetallic element with its ending replaced by the suffix – ide ). Some examples are given in Table \(\PageIndex{2}\). 0 1 NaCl, sodium chloride Na2O, sodium oxide KBr, potassium bromide CdS, cadmium sulfide CaI2, calcium iodide Mg3N2, magnesium nitride CsF, cesium fluoride Ca3P2, calcium phosphide LiCl, lithium chloride Al4C3, aluminum carbide Compounds Containing Polyatomic Ions Compounds containing polyatomic ions are named similarly to those containing only monatomic ions, except there is no need to change to an – ide ending, since the suffix is already present in the name of the anion. Examples are shown in Table \(\PageIndex{2}\). 0 1 KC2H3O2, potassium acetate (NH4)Cl, ammonium chloride NaHCO3, sodium bicarbonate CaSO4, calcium sulfate Al2(CO3)3, aluminum carbonate Mg3(PO4)2, magnesium phosphate Ionic Compounds in Your Cabinets Every day you encounter and use a large number of ionic compounds. Some of these compounds, where they are found, and what they are used for are listed in Table . Look at the label or ingredients list on the various products that you use during the next few days, and see if you run into any of those in this table, or find other ionic compounds that you could now name or write as a formula. Empty DataFrame Columns: [(Ionic Compound, NaCl, sodium chloride, KI, potassium iodide, NaF, sodium fluoride, NaHCO3, sodium bicarbonate, Na2CO3, sodium carbonate, NaOCl, sodium hypochlorite, CaCO3 calcium carbonate, Mg(OH)2, magnesium hydroxide, Al(OH)3, aluminum hydroxide, NaOH, sodium hydroxide, K3PO4, potassium phosphate, MgSO4, magnesium sulfate, Na2HPO4, sodium hydrogen phosphate, Na2SO3, sodium sulfite), (Use, ordinary table salt, added to “iodized” salt for thyroid health, ingredient in toothpaste, baking soda; used in cooking (and as antacid), washing soda; used in cleaning agents, active ingredient in household bleach, ingredient in antacids, ingredient in antacids, ingredient in antacids, lye; used as drain cleaner, food additive (many purposes), added to purified water, anti-caking agent; used in powdered products, preservative)] Index: [] Compounds Containing a Metal Ion with a Variable Charge Most of the transition metals can form two or more cations with different charges. Compounds of these metals with nonmetals are named with the same method as compounds in the first category, except the charge of the metal ion is specified by a Roman numeral in parentheses after the name of the metal. The charge of the metal ion is determined from the formula of the compound and the charge of the anion. For example, consider binary ionic compounds of iron and chlorine. Iron typically exhibits a charge of either 2+ or 3+ (see [link] ), and the two corresponding compound formulas are FeCl 2 and FeCl 3 . The simplest name, “iron chloride,” will, in this case, be ambiguous, as it does not distinguish between these two compounds. In cases like this, the charge of the metal ion is included as a Roman numeral in parentheses immediately following the metal name. These two compounds are then unambiguously named iron(II) chloride and iron(III) chloride, respectively. Other examples are provided in Table \(\PageIndex{3}\). Transition Metal Ionic Compound Name FeCl3 iron(III) chloride Hg2O mercury(I) oxide HgO mercury(II) oxide Cu3(PO4)2 copper(II) phosphate Out-of-date nomenclature used the suffixes – ic and – ous to designate metals with higher and lower charges, respectively: Iron(III) chloride, FeCl 3 , was previously called ferric chloride, and iron(II) chloride, FeCl 2 , was known as ferrous chloride. Though this naming convention has been largely abandoned by the scientific community, it remains in use by some segments of industry. For example, you may see the words stannous fluoride on a tube of toothpaste. This represents the formula SnF 2 , which is more properly named tin(II) fluoride. The other fluoride of tin is SnF 4 , which was previously called stannic fluoride but is now named tin(IV) fluoride. Example \(\PageIndex{1}\): Naming Ionic Compounds Name the following ionic compounds, which contain a metal that can have more than one ionic charge: Fe 2 S 3 CuSe GaN CrCl 3 Ti 2 (SO 4 ) 3 Solution The anions in these compounds have a fixed negative charge (S 2− , Se 2− , N 3− , Cl − , and \(\ce{SO4^2-}\)), and the compounds must be neutral. Because the total number of positive charges in each compound must equal the total number of negative charges, the positive ions must be Fe 3+ , Cu 2+ , Ga 3+ , Cr 4+ , and Ti 3+ . These charges are used in the names of the metal ions: iron(III) sulfide copper(II) selenide gallium(III) nitride chromium(III) chloride titanium(III) sulfate Exercise \(\PageIndex{1}\) Write the formulas of the following ionic compounds: (a) chromium(III) phosphide (b) mercury(II) sulfide (c) manganese(II) phosphate (d) copper(I) oxide (e) chromium(VI) fluoride Answer: (a) CrP; (b) HgS; (c) Mn 3 (PO 4 ) 2 ; (d) Cu 2 O; (e) CrF 6 Summary Chemists use nomenclature rules to clearly name compounds. Ionic and molecular compounds are named using somewhat-different methods. Binary ionic compounds typically consist of a metal and a nonmetal. The name of the metal is written first, followed by the name of the nonmetal with its ending changed to – ide . For example, K 2 O is called potassium oxide. If the metal can form ions with different charges, a Roman numeral in parentheses follows the name of the metal to specify its charge. Thus, FeCl 2 is iron(II) chloride and FeCl 3 is iron(III) chloride. Some compounds contain polyatomic ions; the names of common polyatomic ions should be memorized. Contributors Paul Flowers (University of North Carolina - Pembroke), Klaus Theopold (University of Delaware) and Richard Langley (Stephen F. Austin State University) with contributing authors. Textbook content produced by OpenStax College is licensed under a Creative Commons Attribution License 4.0 license. Download for free at http://cnx.org/contents/85abf193-2bd...a7ac8df6@9.110 ). Modified by Tom Neils (Grand Rapids Community College)