Naming Ionic Compounds

 Naming Ionic Compounds What are the structural units that make up ionic compounds and how are they named? Why? When working in chemistry, it is often convenient to write a chemical in symbols. For example we might write down the substance table salt as NaCl. In talking about chemistry however, it is a bit tacky to say “en-ay see-ell” when we want to refer to a substance. Also, in formal writing we should use the name of the compound rather than its symbols. Therefore we need to learn how to say the proper names of ionic substances.   Model 1 – Ion Charges for Selected Elements  1. Consider the ions of potassium (K) and sulfur (S). Write the chemical formulas for the ionic compound involving these ions, using the simplest ratio(s) of potassium (K) and sulfur (S). Keep in mind that the sum of the charges in an ionic compound must equal zero. K2S 2. Consider the ions of iron (Fe) and sulfur (S). Write chemical formulas for all possible ionic com- pounds involving theseions, using the simplest ratio(s) of iron (Fe) and sulfur (S). Keep in mind that  the sum of the charges in an ionic compound must equal zero. FeS, Fe2S 3  Model 2 – Ionic Compound Names (Metals that form one ion)  NaCl Sodium chloride Zn₃P Zinc phosphide CaS Calcium sulfide Al₂O Aluminum oxide AgS Silver sulfide SrCl Strontium chloride    3. Circle the symbol for the metal in each of the compounds in Model 2. If doing electronically, you can just BOLD the symbol. Remember your PT!  4. Which element comes first in the name and formula of the compounds in Model 2—the metal or the nonmetal? Metal 5. Use the table of ions in Model 1 to answer the following questions: a. In the compound zinc phosphide, what is the charge on the zinc ion? Zn2+ b. In the compound zinc phosphide, what is the charge on the phosphide ion? P3- 6. Explain why a 3 to 2 ratio of ions is necessary for the compound zinc phosphide. There needs to be 3 zinc and 2 phosphorus so that the charge is equal to zero. (2+)(3)=6+ (3-)(2)=6- (6+)+(6-)=0 7. The compound carbon dioxide has a name that gives you a hint as to how many oxygen atoms are in the compound. Is there anything in the name “zinc phosphide” that indicates there are three zinc and two phosphorus ions in the formula for the compound? No 8. Is there any other ratio of zinc and phosphorus ions that could exist? For instance, could you have Zn 2 P or ZnP2 ? Explain your answer. No because the other ratios would result in a charge. 9. Explain why you don’t need to specify the number of ions in the compound when you are naming ionic substances like those in Model 2. If the ion charges are known then you can find the compound without more information and the ions may only form one type of ionic compound so there isn’t a need to put more information in the name. 10. Model 2 is labeled “Metals that form one ion.” What other metals that also form only one ion could be included in the Model 2 list? Model 1 may be helpful in this regard. potassium, magnesium 11. Describe how the names of the nonmetal elements in Model 2 are changed when they are in their anion forms. they end in “ide” 12. Name the following ionic compounds using what you learned from Model 2. Li 2O Lithium oxide MgF2 Magnesium fluoride Al 2S3 Aluminum sulfide K3N Potassium nitride 13. Provide the chemical formula for each of the following ionic compounds. Helpful subscripts to cut-and-paste electronically: Barium chloride   BaCl2  Magnesium oxide MgO   14. Consider the two chemical formulas you wrote in Question 2 for compounds of iron and sulfur. Would the name “iron sulfide” be sufficient to uniquely identify either of those compounds? Explain. Since there are 2 compounds for iron and sulfur the name “iron sulfide” wouldn’t be unique enough to identify a specific type of compound.    Read This! When the metal in an ionic compound always forms an ion with the same charge, you need not indicate that charge as part of the compound name. However, some atoms have the ability to form more than one type of ion. This can make naming confusing. You can’t simply refer to a compound of copper and oxygen as “copper oxide.” People won’t know which compound you are referring to—CuO or Cu 2O.  Model 3 – Ionic Compound Names (Metals that form multiple ions)  15. Model 3 is labeled “Metals that form multiple ions.” What other metals that form multiple ions could be included in Model 3? Model 1 may be helpful in this regard. Mercury, Nickel 16. Describe the most obvious difference between the names in Model 3 and those in Model 2. The roman numerals after the first element. 17. Do the Roman numerals in the names in Model 3 relate to the number of cations or number of anions in the formula unit? Support your answer by citing two specific examples. The roman numerals don’t relate to the number of cations or anions. CuO has (II) and that doesn’t match the number of cations or anions. PbO has (II) and that doesn’t match the number of cations or anions.  18. Keeping in mind that the sum of the charges in an ionic compound must equal zero, use the chemical formulas in Model 3 to answer the following questions: a. Identify the charge on the copper cations in copper(I) oxide and copper(II) oxide, respectively. copper(I) oxide: Cu+ copper(II) oxide: Cu2+ b. Identify the charge on the iron cations in iron(II) chloride and iron(III) chloride, respectively. iron(II) chloride: Fe2+ iron(III) chloride: Fe3+ 19. What do the Roman numerals in the compounds described in Question 19 indicate? The roman numerals describe the charge of the cation.   20. Fill in the table below using what you’ve learned from Model 3.  Compound PbCl 4 Fe2O 3 SnO CuBr2   Charge on Cation Pb4+ Fe 3+ Sn2+ Cu2+ Name of the Compound Lead(IV) chloride Iron(III) oxide Tin(II) oxide Copper(II) bromide