Lab 5 Name How Are Ionic and Covalent Compounds Named and Represented Symbolically? PreLab Assignment There is no written prelab assignment for this laboratory exercise. Recommended: Review the element names, symbols, and ions they form as well as the polyatomic ions. Learning Goals Write the proper name of the ionic or binary covalent compound from the formula. Write the proper formula for the ionic or binary covalent compound from the name. Introduction The first step in naming any compound is to determine whether it is a covalent or ionic compound, since there are different naming rules for each type of compound. Ionic compounds are composed of a cation and and an anion. Since all metals form cations, most ionic compounds consist of a metal and a nonmetal. Exceptions may occur when certain polyatomic ions are involved. Covalent compounds do not contain ions, but share electrons between atoms to form covalent bonds. Covalent compounds are composed solely of nonmetals. ChemActivity: Naming Ionic Compounds From Explorations in Conceptual Chemistry, by Jeffrey Paradis. Answer the following critical thinking questions to help you understand the rules for naming ionic compounds. Part 1 Information: NaCl is called sodium chloride. 1. Ionic compounds contain a metal and a nonmetal. Which is the metal? Which is the nonmetal? 2. Where is the metal written in the formula? 3. Where is the nonmetal written in the formula? 4. What happened to the name of the metal when it went from being a pure element to being part of an ionic compound? 5. What happened to the name of the nonmetal when it went from being a pure element to being part of an ionic compound? 6. Part 1 Summary: What you have learned from Part 1 about naming ionic compounds? Part 2 Information: MgI 2 is called magnesium iodide. 7. Does the name of this compound follow the rules determined in questions 15? 8. What is the charge on the magnesium ion? 9. What does the charge on the magnesium ion have to do with the number of valence electrons that an atom of magnesium has? 10. How many iodide ions are needed to cancel out the charge of a magnesium ion making a neutral compound? 11. How is the number of iodide ions needed in question 10 indicated in the formula?
Lab 5: How Are Ionic and Covalent Compounds Named and Represented Symbolically? 2 12. Part 2 Summary: How are subscripts in formulas for ionic compounds determined? Are they specifically reflected in the name of the compound? Why or why not? Part 3 Information: CuCl is called copper (I) chloride. CuCl 2 is called copper (II) chloride. FeO is called iron (II) oxide. Fe 2 O 3 is called iron (III) oxide. 13. What is the charge on the chloride ion? 14. Knowing the charge on the chloride ion, what must be the charge on the copper ion in the first compound? 15. How is the charge on the copper ion indicated in the name of the first compound? 16. Knowing the charge on the chloride ion, what must be the charge on the copper in the second compound? 17. How is the charge on the copper ion indicated in the name of the second compound? 18. Why do we need to use Roman numerals with transition elements like copper? 19. Why don t we need to use Roman numerals with Group IA and Group IIA elements (and aluminum)? 20. Part 3 Summary: Based on the information from Part 3, what do you think is the general rule for naming main group metals versus transition metals in ionic compounds? Part 4 Information: Na 2 CO 3 is called sodium carbonate. Mg(NO 3 ) 2 is called magnesium nitrate. Pb(NO 2 ) 2 is called lead (II) nitrite. CaCO 3 is called calcium carbonate. NaNO 3 is called sodium nitrate. 21. What do we do to the name of a polyatomic ion when we include it in an ionic compound? Refer to Appendix I on p. 6. (hint: this is simple don t overthink it!) 22. When do we use parentheses in writing the formula for an ionic compound? Your answer should explain why Mg(NO 3 ) 2 has parentheses, but NaNO 3 does not. 23. Will the formula for a compound such as calcium chloride need parentheses? Why or why not?
Lab 5: How Are Ionic and Covalent Compounds Named and Represented Symbolically? 3 Background An ionic compound can be recognized by the presence of a metal and a nonmetal in the formula or name. A covalent compound can be recognized by the presence of two or more nonmetals present in the formula or name. In an ionic compound, metals form positive ions (cations) and nonmetals 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. All compounds are neutral no overall charge. Cations and anions take different forms: Type I metal cations always take the same positive charge. Examples: Na +, Mg 2+, Al 3+ Type II metal cations can vary in charge, but are always positive. Examples: Fe 2+ /Fe 3+, Cu + /Cu 2+ Most representative (main group) elements are Type I and most transition elements are Type II. Exceptions to memorize: Zn 2+, Ag +, Cd 2+ are Type I. Sn 2+ /Sn 4+, Pb 2+ /Pb 4+ are Type II. Polyatomic cations contain groups of atoms acting as a single positive ion. The most common is NH 4 +, ammonium ion. Representative nonmetal anions always take the same negative charge. (e.g. chloride ion is always Cl, oxide ion is always O 2 ) Polyatomic anions contain groups of atoms acting as a single negative ion. There are many see a partial list of polyatomic ions in Appendix I. Writing the name from the formula Flowchart Refer the following flow chart when studying and applying the steps for writing a compound name from its formula. The specific steps are given on the next page. Steps 1. Is the compound ionic or covalent? Ionic compounds contain a cation and an anion. Covalent compounds share electrons in bonds. A. Two or more nonmetals bonded (no metals) is a covalent compound. Exception: polyatomic cation bonded with any anion (e.g. NH 4 Cl, ammonium chloride, is ionic). We will consider only binary covalent compounds here for simplicity (two nonmetals bonded). Note: Acids are a special type of covalent compound that have their own nomenclature rules. Acids will be covered next term. B. A metal and a nonmetal bonded (cation+anion) is an ionic compound. One metal + one nonmetal is a binary ionic compound. One metal + more than one nonmetal is a polyatomic ionic compound. Note: in this course we will not consider two or more metals bonded (no nonmetals).
Lab 5: How Are Ionic and Covalent Compounds Named and Represented Symbolically? 4 2. Use the appropriate rules (ionic or covalent) to name the compound. A. Rules for binary covalent compounds (nonmetals bonded by sharing electrons) List the first element in the formula using a prefix for the number of atoms (except mono). List the second element in the formula using a prefix for the number of atoms as well as the suffix ide. For a list of common prefixes, see Appendix II. Examples: NO is nitrogen oxide; NO 2 is nitrogen dioxide, N 2 O is dinitrogen oxide. (Note that carbon monoxide, CO, is an exception to the rule.) B. Rules for ionic compounds (cation+anion) List cations first, then anions. Note: if there are more than two types of atoms in the formula, a polyatomic ion is present. Cations: name of the metal or polyatomic ion. Type I (only one possible charge on the cation): just the metal name Type II (more than one possible charge on the cation): metal name and Roman numeral corresponding to the charge on the cation Polyatomic ion: memorize the name and formula in order to recognize it. (e.g. NH 4 + is ammonium ion). Anions: in monatomic anion, change ending to ide; if polyatomic ion, use memorized name. e.g. Cl is chlorine, but Cl is chloride. Polyatomic ion: memorize the name and formula (e.g. NO 3 is nitrate ion) Examples: KCl is potassium chloride; KNO 3 is potassium nitrate; NH 4 NO 3 is ammonium nitrate. Writing the formula from the name Steps 1. Is the compound ionic or covalent? 2. Use the appropriate rules (ionic or covalent) to determine the formula from the name. A. For covalent compounds, write the symbols for each nonmetal in the compound name. Include subscripts describing the number of each type of atom in a molecule of the compound as indicated by the prefixes in the name. Examples: sulfur dioxide is SO 2 ; dinitrogen pentoxide is N 2 O 5. B. For ionic compounds: i. Write the symbol for each element or polyatomic ion. ii. Determine the charges on the cation and the anion. iii. If charges are not equal (they do not add to 0), balance the charges to make a neutral formula. To do this, determine how many of each charged particle must be present to balance out to neutral charge. iv. Write the formula with subscripts showing how many of each ion is present in the compound. For polyatomic ions, the same rules apply; if multiple polyatomic ions are needed to balance the formula, use parentheses to show multiple polyatomic ions in the formula. Examples: magnesium oxide manganese (IV) oxide aluminum phosphate calcium phosphate i. & ii. Mg 2+ O 2 Mn 4+ O 2 Al 3+ 3 PO 4 Ca 2+ 3 PO 4 iii. (+2) + (2) = 0 Charges balance. (+3) + (3) = 0 Charges balance. one Mg and one O needed for a neutral compound (+4) + (2)(2) = 0 Must multiply 2 by 2 for charges to balance, so two O 2 ions are needed one Mn and two O needed for a neutral compound one Al and one PO 4 needed for a neutral compound iv. MgO MnO 2 AlPO 4 no parentheses (+2)(3) + (3)(2) = 0 Must multiply +2 by 3 and 3 by 2 for charges to balance three Ca and two PO 4 needed for a neutral compound Ca 3 (PO 4 ) 2 use parentheses to show two PO 4 units Critical Thinking Question 1: If the compound potassium chloride is written in words, how do you know to write the formula with only one potassium and one chloride? Could it be KCl 2 or K 2 Cl? Why or why not?
Lab 5: How Are Ionic and Covalent Compounds Named and Represented Symbolically? 5 Critical Thinking Question 2: Write the formula for potassium oxide. Why do you not need prefixes in the name? (e.g. why not name it dipotassium oxide?) Critical Thinking Question 3: Part A: What is the formula for sulfur dioxide? Sulfur trioxide? Part B: Why do we need prefixes such as di and tri for binary covalent compounds, but not for ionic compounds? Critical Thinking Question 4: Do the formulas CaOH 2 and Ca(OH) 2 describe the same compound? Explain.
Lab 5: How Are Ionic and Covalent Compounds Named and Represented Symbolically? 6 Practice Problems Part A Use the flow chart on p. 2 and the steps on p. 3 as a guide to name the following compounds from their formulas. Chemical Formula Type of Compound Circle One 1 SrS ionic covalent Compound Name 2 Cs 3 PO 4 ionic covalent 3 P 2 O 5 ionic covalent 4 (NH 4 ) 2 SO 4 ionic covalent 5 V 2 O 5 ionic covalent 6 ZnI 2 ionic covalent Part B Use the steps on p. 4 to as a guide to write the formulas for the following compounds from their names. Compound Name Type of Compound Circle One 1 potassium bromide ionic covalent Chemical Formula 2 chromium (IV) chloride ionic covalent 3 barium nitrate ionic covalent 4 sodium hydrogen phosphate ionic covalent 5 dinitrogen tetroxide ionic covalent 6 silver hydroxide ionic covalent Instructor Initials Lab Report Fill in the report sheet on pages 7 and 8. Use this handout as a guide. For each chemical, classify the compound as ionic or covalent. Then use the rules for that type of compound to: write the formula for the compound if the name is given. write the name for the compound if the formula is given. Turn in the pages specified by your lab instructor. Grade breakdown for this lab: 5 points: Full participation and completion of the ChemActivity, CTQs and practice problems. 15 points: Completion of the report sheet on pages 9 10.
Lab 5: How Are Ionic and Covalent Compounds Named and Represented Symbolically? 7 Appendix I: Common Polyatomic Ions *Memorize the polyatomic ions specified by your lecture instructor. Ion Formula + +1 cation NH 4 Ion Name ammonium ion 1 anions C 2 H 3 O 2 CN ClO ClO 2 ClO 3 ClO 4 OH NO 3 NO 2 MnO 4 HCO 3 H 2 PO 4 acetate ion cyanide ion hypochlorite ion chlorite ion chlorate ion perchlorate ion hydroxide ion nitrate ion nitrite ion permanganate ion hydrogen carbonate ion (also called bicarbonate ion) dihydrogen phosphate ion 2 anions CO 3 2 CrO 4 2 Cr 2 O 7 2 2 SO 4 2 SO 3 2 HPO 4 carbonate ion chromate ion dichromate ion sulfate ion sulfite ion hydrogen phosphate ion 3 anions PO 4 3 PO 3 3 phosphate ion phosphite ion Appendix II: Common Prefixes for Covalent Compounds 1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 hepta 8 octa 9 nona 10 deca
Lab 5: How Are Ionic and Covalent Compounds Named and Represented Symbolically? 8
Lab 5: How Are Ionic and Covalent Compounds Named and Represented Symbolically? 9 Name Chemical Formula Type of Compound Circle One 1 KCl ionic covalent Compound Name 2 SO 2 ionic covalent 3 Cr(OH) 3 ionic covalent 4 Na 3 PO 4 ionic covalent 5 NH 4 Br ionic covalent 6 Cd(C 2 H 3 O 2 ) 2 ionic covalent 7 Fe 2 (SO 3 ) 3 ionic covalent 8 NaClO 4 ionic covalent 9 SnF 4 ionic covalent 10 NH 4 NO 3 ionic covalent 11 FeO ionic covalent 12 CCl 4 ionic covalent 13 CaS ionic covalent 14 CsNO 2 ionic covalent 15 SF 6 ionic covalent 16 AgMnO 4 ionic covalent 17 P 4 S 3 ionic covalent 18 SO 3 ionic covalent 19 NaClO ionic covalent 20 Zn(OH) 2 ionic covalent 21 IF 7 ionic covalent 22 CuCr 2 O 7 ionic covalent 23 PbS 2 ionic covalent 24 Al(HCO 3 ) 3 ionic covalent 25 V(CN) 4 ionic covalent
Lab 5: How Are Ionic and Covalent Compounds Named and Represented Symbolically? 10 Name Compound Name Type of Compound Circle One 1 ammonium oxide ionic covalent Chemical Formula 2 silver chloride ionic covalent 3 carbon disulfide ionic covalent 4 strontium iodide ionic covalent 5 cobalt (IV) sulfate ionic covalent 6 barium hydrogen carbonate ionic covalent 7 xenon tetroxide ionic covalent 8 cadmium sulfide ionic covalent 9 copper (II) chlorate ionic covalent 10 copper (I) chlorite ionic covalent 11 bromine pentaiodide ionic covalent 12 magnesium carbonate ionic covalent 13 lithium phosphate ionic covalent 14 aluminum perchlorate ionic covalent 15 iron (III) nitrate ionic covalent 16 magnesium hydride ionic covalent 17 sodium hydroxide ionic covalent 18 nickel (II) sulfate ionic covalent 19 lead (II) acetate ionic covalent 20 tin (IV) cyanide ionic covalent 21 rubidium hypochlorite ionic covalent 22 sulfur hexafluoride ionic covalent 23 potassium dichromate ionic covalent 24 aluminum chlorite ionic covalent 25 triphosphorus tetraselenide ionic covalent