Nomenclature: How to Name Chemicals

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1 Nomenclature: How to Name Chemicals Introduction Many of the chemicals we use at home have common names. Baking soda is used as a rising agent in cookies. Bleach is used to whiten our clothes. Ammonia is a cleaning agent. We season food with salt. Hydrogen peroxide is used to clean out wounds. Each of these chemicals can also be described by their chemical formula and their chemical name. Baking soda is NaHCO 3 or sodium bicarbonate. Bleach is NaClO or sodium hypochlorite. Ammonia is NH 3 or nitrogen trihydride. Salt is NaCl or sodium chloride. Hydrogen peroxide is H 2 O 2 and its common name is also its chemical name. Chemical formulas express the exact composition of chemical substances. The composition of a CO 2 molecule is always 1 carbon atom and 2 oxygen atoms. The chemical name for CO 2 is carbon dioxide. Every scientist in the world, upon reading or hearing the word carbon dioxide, knows that you are referring to the chemical formula, CO 2. There is a recognized system for naming chemical substances that is based on chemical composition and structure. In this lesson, we will be using nomenclature rules to name chemical compounds. After completing this lesson, you will be able to: Name binary compounds of a metal and a nonmetal Name binary compounds containing only nonmetals Name Type I, Type II, and Type III binary compounds Name the common polyatomic ions Name compounds Name acids and bases Write chemical formulas from chemical names

2 Naming Ions In many cases, compound names are derived from the names of the ions that make up the compound. To be fluent in chemistry, you need to know the names of the most common ions. Three types of ions are the most useful in naming compounds and predicting the products of reactions. They are presented in the following Tables 5.1, 5.2 and 5.4 from your textbook. Table 5.1: Simple cations, or positively charged ions, that have a set ionic charge are named as their element name. So K + is called the potassium ion. Simple anions, or negatively charged ions, that have a set ionic charge, are named with the element root with an ide added to the end of the root. So Cl - is called the choride ion. If the charge on an ion is only +1 or -1, you do not need to write the number 1 as part of the charge. The symbol + or infers that the charge is 1. Note that hydrogen can form both a positive ion called hydrogen, and a negative ion called hydride. When hydrogen forms compounds with positively charged metal ions, it becomes the negatively charged hydride ion. Titanium hydride, TiH 2, and lithium hydride, LiH, are examples of metal hydrides.

3 Table 5.2: Some metals can form ions of multiple charges. These are the Type II cations. They are named with the element name and the charge listed within parentheses as a Roman numeral. For example, either 1 or 2 copper atoms can combine with an oxygen atom depending on the conditions of the reaction environment. If the compound formed is CuO, the copper ion has a charge of +2 because the oxygen ion has a set charge of -2. The copper ion is Cu 2+ and is called copper(ii). If the compound formed is Cu 2 O, the copper ion has a charge of +1 because there are 2 copper ions to balance the oxygen ion charge of -2. The copper ion is Cu + and is called copper(i). The older names are shown in Table 5.2 so you can see where the symbols originally came from. In this course, always use the Roman numeral form of the name.

4 Table 5.4: Polyatomic ions are groups of atoms that share a charge. You must learn to recognize these groups in compounds as they have specific names. SO 4 2- is the sulfate ion. The sulfate ion has a charge of -2. So you would look at the compound CaSO 4 as the Ca 2+ ion and the SO 4 2- ion.

5 Nomenclature Flowchart Compounds refer to pure substances made up of 2 or more types of atoms with a constant composition. One familiar ionic compound is NaCl which is sodium chloride, or common salt. Another ionic compound is Fe 2 O 3 which is iron (III) oxide or rust. Chalk is a pressed ionic compound, CaCO 3, which is calcium carbonate. An example of a molecular compound is CO 2 which is carbon dioxide, a product of respiration. The Nomenclature Flowchart can be used to correctly name each of these four chemical compounds. NaCl: Start at the Chemical Formula box on the Nomenclature Flowchart. NaCl is made up of a metal and a nonmetal, the metal has a single charge, so name the metal as sodium. There is only one nonmetal, so name the nonmetal with an ide ending as chloride. The name is sodium chloride. Fe 2 O 3 : Start at the Chemical Formula box on the Nomenclature Flowchart. Fe 2 O 3 is made up of a metal and a nonmetal, but the metal is a multiple charge metal, so you must name the metal using a Roman numeral to indicate the charge. There are 3 oxygen atoms in the formula and each oxygen has a charge of -2 for a total charge of -6. Since the compound has to have an overall neutral charge of 0, there must be a total charge of +6 from the iron. There are 2 iron atoms in the formula, so each iron atom must have a charge of +3. The metal is named iron (III). There is only one type of nonmetal, so name the nonmetal with an ide ending as oxide. The name is iron (III) oxide. CaCO 3 : Start at the Chemical Formula box on the Nomenclature Flowchart. CaCO 3 is made up of a metal and 2 nonmetals. The metal has a single charge, so name the metal as calcium. There are more than one nonmetal, so name the polyatomic ion as carbonate. The name is calcium carbonate. CO 2 : Start at the Chemical Formula box on the Nomenclature Flowchart. CO 2 is made up of 2 nonmetals. The first element in the formula is carbon and there is only one carbon. When there is only one of the first element present, do not use the greek prefix mono to start the name, just name the single element as carbon. There are 2 of the second element so use the greek prefix and an ide ending to name dioxide. The name is carbon dioxide.

6 Naming Acids HCl (g) is the gas called hydrogen chloride. The subscript (g) indicates that the hydrogen chloride is in the gaseous phase. If HCl (g) is bubbled through water, it dissolves and forms HCl (aq) an acid called hydrochloric acid. The subscript (aq) indicates that the HCl is in the aqueous state or phase. That means that the HCl has separated into the H + ion and the Cl - ion in the water. Whenever you see the (aq) subscript, you know that the substance has dissociated (separated) into its ionic components. Whenever you see a substance that starts with H, hydrogen, and is in an aqueous state, you probably have an acid. Acids that contain oxygen are named differently from acids that don t have oxygen in their formula. To name an acid, first look at its anion, or negative ion. If the anion does not contain oxygen: Start with Hydro- Identify the anion Add ic to the end of the anion root Ex: HCl (aq) : The anion is Cl - or chloride, so the acid is Hydrochloric acid If the anion contains oxygen: Identify the anion or negative polyatomic ion Look at the ending of the anion If the anion ends in ite, use the anion root and -ous Ex: HNO 2(aq) : NO 2 - is the nitrite polyatomic ion, so the acid is Nitrous acid If the anion ends in ate, use the anion root and -ic Ex: H 2 SO 4(aq) : SO 4 2- is the sulfate polyatomic ion, so the acid is Sulfuric acid There are a few common acids that are used frequently. It is best to memorize these acids. Acids without oxygen Formula Acids with oxygen Formula Hydrofluoric acid HF Nitric acid HNO 3 Hydrochloric acid HCl Nitrous acid HNO 2 Hydrobromic acid HBr Sulfuric acid H 2 SO 4 Hydroiodic acid HI Sulfurous acid H 2 SO 3 Hydrocyanic acid HCN Phosphoric acid H 3 PO 4 Hydrosulfuric acid H 2 S Acetic acid HC 2 H 3 O 2

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