1 Chapter 4 Compounds and Their Bonds 4.2 Ionic Compounds Copyright © 2009 by Pearson Education, Inc.

2 Ionic compounds consist of positive and negative ions. have attractions called ionic bonds between positively and negatively charged ions. have high melting and boiling points. are solid at room temperature. Ionic Compounds

3 Salt Is An Ionic Compound Sodium chloride or “table salt” is an example of an ionic compound.

4 An ionic formula consists of positively and negatively charged ions. is neutral. has charge balance. total positive charge = total negative charge The symbol of the metal is written first, followed by the symbol of the nonmetal. Ionic Formulas

5 Charge Balance for NaCl, “Salt” In NaCl, a Na atom loses its valence electron. a Cl atom gains an electron. the symbol of the metal is written first, followed by the symbol of the nonmetal.

6 Charge Balance in MgCl2 In MgCl 2, a Mg atom loses 2 valence electrons. two Cl atoms each gain 1 electron. subscripts indicate the number of ions needed to give charge balance. Copyright © 2009 by Pearson Education, Inc.

7 Charge Balance in Na 2 S In Na 2 S, two Na atoms lose 1 valence electron each. one S atom gains 2 electrons. subscripts show the number of ions needed to give charge balance. Copyright © 2009 by Pearson Education, Inc.

8 Writing Ionic Formulas from Charges Charge balance is used to write the formula for sodium nitride, a compound containing Na + and N 3−. Na + 3Na + + N 3− = Na 3 N Na + 3(+1) + 1(3-) = 0

9 Write the ionic formula of the compound with Ba 2+ and Cl . Write the symbols of the ions. Ba 2+ Cl  Balance the charges. Ba 2+ Cl  two Cl - needed Cl  Write the ionic formula using a subscript 2 for two chloride ions. BaCl 2 Formula from Ionic Charges

10 Select the correct formula for each of the following ionic compounds. A. Na + and O 2- 1) NaO 2) Na 2 O3) NaO 2 B. Al 3+ and Cl - 1) AlCl 3 2) AlCl 3) Al 3 Cl C. Mg 2+ and N 3- 1) MgN 2) Mg 2 N 3 3) Mg 3 N 2 Learning Check

11 A. Na + and O 2- 2) Na 2 O check: 2Na + + O 2- = 2(1+) + 1(2-) = 0 B. Al 3+ and Cl - 1) AlCl 3 check: Al 3+ + Cl - = (3+) + 3(1-) = 0 C. Mg 2+ and N 3- 3) Mg 3 N 2 check: 2Mg 2+ +2N 3- = 2(3+) + 2(3-) = 0 Solution