Chemical Nomenclature

Transcription

1 Chemical Nomenclature Many everyday and historically important chemical compounds have common names. For example, water is the common name for H 2 O, baking soda is the common name for NaHCO 3 and KNO 3, an important component of gunpowder, is known as saltpeter. However, since there are over 50 million known chemical compounds, learning a common name for each one would be very difficult. Chemical nomenclature is a systematic method of naming chemical compounds. Having a system for naming means that we don t have to learn 50 million names, we only have to learn the rules for naming. It also allows scientists who speak different languages to communicate effectively. The rules for chemical nomenclature come from the International Union for Pure and Applied Chemistry (IUPAC), a group made up of chemists from all over the world. In this exercise you will learn rules for naming ionic and covalent compounds and learn to predict the ratios that chemicals combine in based on their ionic charge. A. Naming Type I Binary Ionic Compounds Type I binary ionic compounds are made of (1) a metal that can only have one possible charge and (2) a nonmetal. The metal is the cation, or positively charged ion and the nonmetal is the anion, or negatively charged ion. In the chemical formula, the cation is always written first and the anion is written second. Cations that fall under Type I naming include Group 1A alkali metals, which always form 1+ cations and Group 2A alkaline earth metals which always form 2+ cations. Most transition metals fall under Type II naming, discussed below, but the exceptions are silver (Ag), which always forms 1+ cations and zinc (Zn) and cadmium (Cd), which always form 2+ cations. In naming a Type I binary ionic compound, the cation gets written first using its full element name. The anion is written second using the stem of its element name and adding an ide ending. For instance, fluorine becomes fluoride and oxygen becomes oxide. Examples: NaCl sodium chloride MgBr 2 magnesium bromide Ionic compounds are electronically neutral, meaning the charges on the anions and cations balance to zero. To determine a formula from a chemical name, you must first determine the charges on the ions in the compound and then figure out how many of each are needed to balance the charges. For instance calcium chloride is made of Ca 2+ and Cl ions. For the charges to balance there need to be two Cl ions, which makes the formula CaCl 2

2 B. Naming Type II Binary Ionic Compounds Type II binary ionic compounds are made of (1) a metal that can have more than one possible charge and (2) a nonmetal. Type II cations are typically transition metals. For instance, Iron form either Fe 2+ or Fe 3+ cations. Two nontransition metal elements that form more than one ion are Tin (Sn) and Lead (Pb). Iron can form two compounds with chlorine: Fe 2+ forms FeCl 2, Fe 3+ forms FeCl 3. These are two different compounds with different physical and chemical characteristics. (For example, FeCl 2 has a melting point of 306 C, while FeCl 3 melts at 677 C.) Therefore, we cannot simply call both compounds iron chloride. Type II naming allows us to distinguish between the two compounds. Type II cations get named as their full element name plus a Roman numeral in parentheses representing the cation charge. For instance, Fe 2+ gets named Iron (II) and Fe 3+ gets named Iron (III). The anion is written as the ide form of the element. Examples: CuO copper (II) oxide SnCl 4 tin (IV) chloride C. Naming Ionic Compounds with Polyatomic Ions Polyatomic ions are ions composed of two or more covalently bonded atoms that can be thought of as a single unit (they do not break up further in water). Ionic compounds that have three or more elements are generally composed of a metal cation and polyatomic anion. Ammonium (NH 4 + ) is the only common polyatomic cation. The names, formulas and charges of polyatomic ions must be memorized (see table of common polyatomic ions below). Ionic compounds with polyatomic ions get named in the same way as Type I and II binary ionic compounds with the name of the polyatomic ion in the place of the anion name. If more than one polyatomic ion is needed to balance the charges, the whole ion gets put in parentheses. Examples: Li 2 CO 3 lithium carbonate Pb(NO 3 ) 2 lead (II) nitrate NH 4 Cl ammonium chloride Ions with 1 charge NO 2 Nitrite NO 3 Nitrate ClO Hypochlorite ClO 2 Chlorite ClO 3 Chlorate ClO 4 Perchlorate CN Cyanide OH Hydroxide MnO 4 Permanganate HSO 4 Hydrogen sulfate HCO 3 Hydrogen carbonate H 2 PO 4 Dihydrogen phosphate NCS Thiocyanate C 2 H 3 O 2 Acetate Ions with 2 charge 2 SO 3 Sulfite 2 SO 4 Sulfate 2 HPO 4 Hydrogen Phosphate 2 CO 3 Carbonate 2 CrO 4 Chromate 2 Cr 2 O 7 Dichromate 2 C 2 O 4 Oxalate 2 O 2 Peroxide Ions with 3 charge PO 4 3 Phosphate Ions with 1+ /2+ charge + NH 4 Ammonium 2+ Hg 2 Mercury(I)

3 D. Naming Binary Covalent compounds Binary covalent compounds are made of two nonmetals, as opposed to a metal and a nonmetal. The system for naming covalent compounds is different from the one for ionic compounds and it is important to keep the two systems separate. To name a covalent compound, the first element is written as its element name, the second element is written as its ide form, and both elements get a prefix that indicates the number of each element in a compound. If the prefix of the first element is mono, the prefix is dropped. Prefixes 1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 hepta 8 octa 9 nona 10 deca Examples: P 2 S 5 diphosphorous pentasulfide N 2 O dinitrogen monoxide NO 2 nitrogen dioxide In naming a binary covalent compound, the first element in the name is the one farthest to the left in the periodic table (ex: carbon dioxide). If both elements in the compound are in the same group in the periodic table, the element towards the bottom of the periodic table is written first (ex: sulfur dioxide). Hydrogen is sometimes written first and sometimes written second in binary covalent compounds. Some binary covalent compounds are always referred to using their common names. Important examples are: H 2 O water H 2 O 2 hydrogen peroxide NH 3 ammonia H 2 S hydrogen sulfide CH 4, methane E. Naming Acids Acids can be thought of as substances that release H + ions when dissolved in water. Chemical formulas of acids contain one or more H + ions and an anion the ending of the anion determines how the acid is named. If the anion has an ide ending (i.e. chloride, cyanide), the hydro prefix gets added to the anion name and ide is replaced with ic acid. If the anion ends in ate (i.e. chlorate), the ate is replaced with ic acid. If the anion ends in ite (i.e. sulfite), the ite is replaced with ous acid. Examples: Acid Anion Name HCl (aq) chloride (Cl ) hydrochloric acid HClO 3 (aq) chlorate (ClO 3 ) chloric acid HClO 2 (aq) chlorite (ClO 2 ) chlorous acid

4 Determining Which Naming Method to Use: Formula to Name Name to Formula

5 Chemical Nomenclature: Worksheet Name A. Name the following compounds: Al₂S₃ NaH₂PO₄ Ca(ClO) 2 Mn(HCO₃)₄ Ni(ClO)₂ Cr(OH)₃ Zn(HSO₄)₂ HNO 3 (aq) NO₃ SnCrO₄ Li 2 SO₄ Mg(ClO 2 )₂ ZnS NH₄ClO 3 Cu(MnO₄)₂ NaClO Co₂(SO₃)₃ HCl (aq) HClO₄ (aq) N₂O Fe₂S₃ (NH₄) 3 PO₄ PbO NaOH NiBr₂ Report Page 1 of 2

6 Chemical Nomenclature: Worksheet Name B. Write the formulas for the following compounds: manganese(ii) chlorite chlorine monoxide potassium nitride mercury(ii) sulfate cobalt(iii) sulfite calcium chlorite nickel(ii) carbonate silicon monoxide diphosphorus pentoxide carbonic acid cobalt(ii) permanganate lead(iv) nitrate barium sulfite hypochlorous acid lead(ii) sulfide iron(iii) chloride zinc permanganate manganese(ii) bromide nitrous acid xenon pentoxide silver nitrate phosphorous pentchloride potassium cyanide Report Page 2 of 2