Purpose: Theory: Nomenclature and Formulas of Ionic Compounds 1. To become familiar with the rules of chemical nomenclature, based on the classification of compounds. 2. To write the proper name of the compound when given the formula. 3. To write the proper formula when given the name. Metals form positive ions (cations) and non-metals form negative ions (anions). Chemical Formulas of ionic compounds result from combining cations with anions in ratios that result in a net charge of zero for the compound. Chemical Nomenclature depends on the types of cations and anions present. Cations and anions take different forms: Representative Metal Cations always take the same positive charge. (Groups 1a, 2a, Al +3, Zn +2, Cd +2 ) Transition Metal Cations can vary in charge, but are always positive. ( Examples: Fe 2+ and Fe 3+ ) Polyatomic cations contain groups of atoms acting as a single positive ion. ( Most common is NH4 +1 ) Representative Nonmetal Anions always take the same negative charge. (Groups 5a, 6a, 7a) Polyatomic anions contain groups of atoms acting as a single negative ion. (The list is extensive) Names of ionic compounds depends on recognizing the type of cation and anion present. Each type employs a different set of rules for writing names. It is absolutely importanct to get the right classification, since using the wrong set of rules will result in an improper name. There are several approaches to Nomenclature. The following is a summary of the common sets of rules found in most textbooks. NOTE: For best results, keep a periodic table handy. Section I: Writing the Name from the Formula If the formula contains: The compound is: Go to: One metal element and Binary Part 1--Binary Compounds One nonmetal element More than two elements Polyatomic Part 2--Polyatomic Ions Hydrogen as the first An Acid Part 3--Acids element Page 1
Section I: Writing the Name from the Formula Part 1. Binary Ionic Compounds ----> Is the metal is representative or transition? a. Representative Metal Cation + Representative Nonmetal Anion. Includes: Metals: Groups 1a, 2a, Al (also Ag, Zn, Cd) Nonmetals: Groups 7a, 6a, (and sometimes 5a) 1a 2a 3a 4a 5a 6a 7a Li Be N O F Na Mg Al P S Cl K Ca Zn Br Rb Sr Ag Cd I Cs Ba Fr Ra Rule: State the name of the metal, change the nonmetal ending to -ide. NaCl CdBr2 SrS Al2O3 Sodium chloride Cadmium Bromide Strontium sulfide Aluminum oxide b. Transition Metal Cation + Representative Nonmetal Anion Includes: Metals: Most d-block transition metals, Sn, Pb, U Nonmetals: Groups 7a, 6a, and sometimes 5a 1a 2a 3a 4a 5a 6a 7a N O F P S Cl Sc Ti V Cr Mn Fe Co Ni Cu Br Sn I Pt Au Hg Pb Rule: State the name of the metal Determine the charge of the cation, based on known charge of the anion. Write the charge in Roman Numerals placed in brackets. Change the nonmetal ending to -ide. CuBr Fe2O3 HgCl2 PbS2 Cu +1 Br -1 Fe +3 O -2 Hg +2 Cl -1 Pb +4 S -2 Copper[I] bromide Iron [III] oxide Mercury [II] chloride Lead [IV] sulfide Page 2
Section I: Writing the Name from the Formula Part 2. Polyatomic Ions ----> Ionic compounds containing more than two elements. Table of Common Polyatomic Ions Ammonium ion NH4 +1 (This is the only common polyatomic cation.) Acetate ion C2H3O2-1 (Sometimes written CH3COO -1 ) Bicarbonate ion HCO3-1 (aka Hydrogen Carbonate ion) Carbonate ion CO3-2 Nitrate ion NO3-1 Nitrite ion NO2-1 Phosphite ion PO3-3 Phosphate ion PO4-3 Monohydrogen Phosphate HPO4-2 Dihydrogen Phosphate H2PO4-1 Sulfite ion SO3-2 Sulfate ion SO4-2 Hypochlorite ion ClO -1 Cyanide ion CN -1 Chlorite ion ClO2-1 Hydroxide ion OH -1 Chlorate ion ClO3-1 Peroxide ion O2-2 Perchlorate ion ClO4-1 Permanganate ion MnO4-1 a. Representative Metal Cation + Polyatomic Anion Rule: State the name of the metal, then the name of the polyatomic ion. Na2SO4 Ca(CN)2 LiC2H3O2 Zn3(PO4)2 Sodium sulfate Calcium cyanide Lithium acetate Zinc phosphate b. Transition Metal Cation + Polyatomic Ion Rule: State the name of the metal, with the Roman Numeral charge in brackets, followed by the name of the polyatomic ion. Sn(OH)2 Co (NO3)6 Ni (C2H3O2)5 AuPO4 Sn +2 (OH) -1 Co +6 (NO3) -1 Ni +5 (C2H3O2) -1 Au +3 (PO4) -3 Tin [II] hydroxide Cobalt [VI] nitrate Nickel [V] acetate Gold[III] phosphate c. Ammonium ion ( NH4 +1 ) Rule: Start the name with Ammonium, followed by the name of the anion. NH 4 Cl (NH 4 ) 2 O NH 4 C2H3O2 (NH 4 ) 3 PO4 Ammonium chloride Ammonium oxide Ammonium acetate Ammonium phosphate Page 3
Section I: Writing the Name from the Formula Part 3. Acids--Contain hydrogen as the positive ion. A. Binary Acids -- contain hydrogen plus one nonmetal element. (NO oxygens) Rule: a. Begin the name with hydro-. b. Change the ending to -ic. c. Add the word acid to the end. HF HCl HBr HI H2S Hydrofluoric Hydrochloric Hydrobromic Hydroiodic Hydrosulfuric Acid Acid Acid Acid Acid B. Ternary Acids (Oxy-Acids) -- Formula begins with hydrogen, and contains oxygen. Rule: a. Identify the polyatomic ion, and change the ending as follows: Formula Name Acid nomenclature C2H3O2-1 Acetate Acetic SO3-2 Sulfite Sulfurous SO4-2 Sulfate Sulfuric NO2-1 Nitrite Nitrous NO3-1 Nitrate Nitric PO3-3 Phosphite Phosphorous PO4-3 Phosphate Phosphoric ClO -1 Hypochlorite Hypochlorous ClO2-1 Chlorite Chlorous ClO3-1 Chlorate Chloric ClO4-1 Perchlorate Perchloric b. Add the word acid to the end. H2SO4 H2SO3 HNO3 H3PO4 Sulfuric acid Sulfurous acid Nitric acid Phosphoric acid Page 4
Section 2--Writing the Formula from the Name Metal is: And ends in: The compound is: Go to: Representative -ide Binary Part 1 (Groups 1a, 2a, or Ag, Cd, Zn) NOT -ide Polyatomic Part 3 Roman Numeral -ide Transition metal Part 2 (Most transition metals) NOT ide Polyatomic Part 3 Acids Part 4 Part 1 -- Formulas of Binary Ionic Compounds with Representative Elements Includes: Metals: Nonmetals: Group 1a ( Li +1, Na +1, K +1, Rb +1, Cs +1, Fr +1 ) Group 7a ( F -1, Cl -1, Br -1, I -1 ) Group, 2a (Be +2, Mg +2, Ca +2, Sr +2, Ba +2, Ra +2 ) Group 6a ( O -2, S -2 ) Group 3a (Al +3 only) Group 5a (N -3, P -3 ) Also ( Ag +1, Zn +2, Cd +2 ) How to Proceed: Magnesium Oxide a. Write the Symbols of both elements... Mg O (Metal first, followed by the nonmetal ) b. Determine the charge of the ions from... Mg +2 O -2 their positions on the Periodic Table. c. Cross multiply to balance the charges... Mg +2 O -2 2 2 d. Reduce the formula if necessary... Mg2O2 MgO Page 5
Section 2, Writing the Formula From the Name Part 2 --Formulas of Binary Ionic Compounds with Transition Metals Includes: Most d-block metals; Sn, and Pb. (For d-block, exceptions, see part 1, above.) How to Proceed: Manganese (IV) Oxide a. Write the Symbols of both elements... Mn O b. Determine the charge of the transition... Mn 4+ metal ion from the Roman Numeral. Use the Periodic Table to determine... O -2 the charge of the Nonmetal. c. Cross multiply to balance the charges... Mn 4+ O -2 2 4 d. Reduce the formula, if necessary... Mn2O4 MnO2 Part 3--Polyatomic Ions : Includes: At least one polyatomic ion Consult the list of common polyatomic ionsgiven above, or in other texts. How to Proceed Cobalt [VI] Phosphate a. Write the symbols for the ions.... Co PO4-3 b. Determine the charge of the metal... Co +6 ion using the rules from Pts. 1&2 c. Cross multiply to balance the charges... Co +6 PO4-3 3 6 d. Use parentheses to enclose the polyatomic ion if needed... Co3 (PO4)6 e. Reduce, if necessary... Co(PO4)2 Page 6
Section 2, Writing the Formula from the Name. Part 4. Acids A. Binary Acids -- Contain the prefix hydro-. Hydrofluoric acid How to Proceed: a. The name gives the component elements... (H +1 ) (F -1 ) b. Balance the charges as with ionic compounds... HF B. Ternary Acids (Oxy-acids) -- Do NOT contain the prefix hydro-. How to Proceed a. Match the ending with the proper polyatomic ion. (Use the Table in Section 1 above) b. Look for the polyatomic ion containing the element, and the proper ending. Sulfuric Acid Sulfurous Acid Sulfate Ion (SO4-2 ) Sulfite Ion (SO3-2 ) c. Balance the negative charge with the same number of H+. H2 SO4 H2 SO3 Page 7 END