CHEMICAL NOMENCLATURE

Transcription

1 CHEMICAL NOMENCLATURE Chemical nomenclature The process of giving unambiguous chemical formulas or chemical names to elements and compounds Introduction Chemistry is the study of matter (elements and compounds) and the changes that matter undergoes. Since elements and compounds are such an important part of chemistry, and because there are so many different elements (109 at the present time) and compounds ( hundreds of thousands), it is very important that chemists be able to communicate concisely and without ambiguity which element or compound is being discussed. In the early beginnings of chemistry, the chemical name of a compound and its chemical formula had little or no relationship to each other. For example the compound Na 2 CO 3, was initially called soda ash. The name soda ash contains no information about the type or number of elements in the compound. Modern naming methods have corrected this lack of connection between chemical formulas and chemical names. Today the rules for writing chemical formulas and naming chemicals are set by the Nomenclature Committee of the International Union of Pure and Applied Chemistry (IUPAC). Chemical names and formulas that follow the rules of this committee are said to follow IUPAC nomenclature. The older names are often referred to as common names. Thus soda ash is the common name for Na 2 CO 3 and sodium carbonate is the correct IUPAC name. In Chemistry 1180 you will occasionally encounter a common name, water for example, but most of the nomenclature will follow IUPAC rules. In this course you will be expected to master the IUPAC nomenclature for five different types of compounds. These are binary compounds (both metalnonmetal and nonmetal nonmetal), metalpoly atomic anion, binary acids ( non oxyacids), poly atomic acids ( oxyacids) and hydrates. IUPAC Nomenclature Rules for Inorganic Compounds Metal Nonmetal 1. Binary Compounds These compounds may be either ionic or covalent depending on the electronegativity of M and X. The metal or NH 4 is always written first. These compounds are commonly referred to as salts. General form = M y X z Where: M = any metal ion or ammonium ion, NH 4 X = any nonmetal element and OH 1 or CN 1 y and z represent small integers

2 Steps in naming binary metal nonmetal compounds: (1) Use the full name of the metal, M, or ammonium if M is NH 4 (2) Follow metal name with a Roman numeral, in ( ), to indicate the metal's oxidation state. This step is omitted if the metal has only one common oxidation state (see periodic chart). (3) Write the stem of the nonmetal's name, or hydroxide if OH or cyanide if CN. Stems for the most common nonmetals are as follows: B=bor, C=carb, N=nitr, O=ox, F=fluor, Si=silic, P=phosph, S=sulf, Cl=chlor, As=arsen, Se=selen, Br=brom, Te=tellur, I=iod (4) Add the suffix, ide, to the stem of the nonmetal. Examples: NaCl = Sodium Chloride; Fe 2 O 3 = Iron (III) oxide; Ag 3 N = Silver Nitride Nonmetal Nonmetal These compounds are always covalently bonded. They are commonly referred to as covalent or molecular compounds. The least electronegative element ( see periodic chart) is usually written first. General form = Q y X z Steps in naming binary covalent compounds: Where: Q = any nonmetal and X = a different nonmetal y and z are small integers (1) Write the numerical prefix for y ( see prefix list below )unless it is one(1) then no numerical prefix is used. (2) Add the full name of the nonmetal, Q. (3) Write the numerical prefix of z. Once again, no numerical prefix is used if z=1. (4) Add the stem of the name for the second nonmetal, X. (5) Complete the name by adding the suffix, ide, to the stem; (6) If the first element is hydrogen, H, no numerical prefixes are needed. Most commonly used numerical prefixes: 1 = mono; 2 = di; 3 = tri; 4 = tetra; 5 = penta; 6 = hexa; 7 = hepta; 8 = octa; 9 = nono; 10 = deca Examples: ICl = Iodine chloride ; ICl 3 = Iodine trichloride ; N 2 O 4 = Dinitrogen tetraoxide Cation (Metal or NH 4 ) polyatomic anion Please note: From this point on, it is very important that you have memorized the correct name, formula and charge for all the polyatomic anions listed at the end of this document. General form = (Metal ion or NH 4 ) y (Polyatomic anion) z

3 The bond between the metal ion or ammonium ion and the polyatomic anion is always ionic. These compounds are, like the binary metalnonmetal compounds, also referred to as salts. Steps in naming cationpolyatomic anion compounds: (1) Name the metal ion/ammonium ion in exactly the same manner used in the naming of binary metalnonmetal compounds. (2) Name the polyatomic anion. Examples: Na 2 SO 4 = Sodium sulfate; Cu 3 (PO 4 ) 2 = Copper(II) phoshate (NH 4 ) 2 CO 3 = ammonium carbonate Binary Acids ( acids without oxygen) ACIDS General form: H y X(aq) Where: H = hydrogen and X = a nonmetal y is a small integer (aq) means that the compound is dissolved in water. Steps in naming binary acids: (1) Write the prefix, hydro; (2) Add the stem of the name for the nonmetal, X. If X= sulfur, use the entire name instead of the stem. (3) Add the suffix, ic to the stem. (4) Add the word, acid. Examples: HF(aq) = hydrofluoric acid; H 2 S(aq) = hydrosulfuric acid Oxyacids ( acids of polyatomic anions) General form: H y XO z (aq) Where: H = hydrogen and XO y z = a polyatomic anion y and z are small integers (aq) means that the compound is dissolved in water. Steps in naming oxyacids: (1) Write the stem of the anion. (The stem of most polyatomic anions is the name of the anion minus the ate or ite ending.) Example: ClO 4 = perchlorate ion, stem = perchlor (2) If the anion name ended in ate, add ic to the stem. (3) If the anion name ended in ite, add ous to the stem. (4) Add the word, acid. Examples: HClO 4 (aq) = perchloric acid; HNO 2 (aq) = nitrous acid; HIO(aq) = hypoiodous acid

4 Hydrates General form: Salt Cy H 2 O Where y = a small whole number. Steps in naming hydrates: (1) Name the salt (2) Give the numerical prefix for the value of y. (3) Add the word hydrate. Examples: CuSO 4 C 5H 2 O = copper (II) sulfate pentahydrate ZnF 2 C 4H 2 O = zinc fluoride tetrahydrate

5 Polyatomic Ions (Formulas) NH 4 NO 2 2 C 2 O 4 C 2 H 3 O 2 OH 2 SO 3 N 3 3 PO 4 2 O 2 2 CO 3 2 CrO 4 CN 2 S 2 O 3 3 BO 3 NO 3 MnO 4 ClO ClO 4 ClO 3 2 SO 4 2 Cr 2 O 7 3 AsO 4 HCO 3 HSO 4 2 H PO 4 H 2 PO 4 ClO 2 OF BrO BrO 2 BrO 3 BrO 4 IO IO 3 IO 4 Polyatomic Ions (Names) oxalate ion hydroxide ion sulfate ion peroxide ion phosphate ion ammonium ion arsenate ion acetate ion chlorate ion nitrite ion dichromate ion chlorite ion carbonate ion sulfite ion chromate ion cyanide ion nitride ion borate ion perchlorate ion nitrate ion hypochlorite ion permanganate ion thiosulfate ion hydogen sulfate ion bicarbonate or hydrogen carbonate ion hydrogen phosphate ion dihydrogen phosphate ion ***Please Note: The anions, OF, BrO, BrO 2, BrO 3, BrO 4, IO, IO 3 and IO 4 are named in the same manner as the chlorine series. For example: ClO 3 = chlorate ion BrO 3 = bromate ion IO 3 = iodate ion