1. © 2014 Pearson Education, Inc. Chapter 6 Lecture Basic Chemistry Fourth Edition Chapter 6 Ionic and Molecular Compounds 6.2 Writing Formulas for Ionic Compounds Learning Goal Using charge balance, write the correct formula for an ionic compound.

2. © 2014 Pearson Education, Inc. Ionic Compounds Ionic compounds consist of positive and negative ions. Ions are held together by the strong electrical attractions between opposite charges, called an ionic bond. Noble gases have a stable electron configuration and do not form ionic compounds.

3. © 2014 Pearson Education, Inc. Properties of Ionic Compounds The physical and chemical properties of elements change when they react to form ionic compounds.

4. © 2014 Pearson Education, Inc. Properties of Ionic Compounds Figure 6.1 The elements sodium and chlorine react to form the ionic compound sodium chloride, the compound that makes up table salt. The magnification of NaCl crystals shows the arrangement of Na + ions and Cl – ions in a crystal of NaCl.

5. © 2014 Pearson Education, Inc. Chemical Formulas of Ionic Compounds The chemical formula of a compound represents the symbols and numbers of atoms or ions in the lowest whole-number ratio. The sum of the ionic charges is always zero.

6. © 2014 Pearson Education, Inc. Subscripts in Formulas Two chlorine atoms are needed to react with one magnesium atom to give the compound magnesium chloride (MgCl 2 ) charge balance. Subscripts in an ionic compound represent the lowest number of positive and negative ions that give an overall charge of zero.

7. © 2014 Pearson Education, Inc. Writing Ionic Formulas from Ionic Charges To write the formula of a compound that contains Na + and S 2− metal ions are written first, followed by an ion from a nonmetal two Na + ions needed for charge balance are represented using a subscript in the formula the subscript for the nonmetal S 2− is 1 (it is understood and not written in the formula)

8. © 2014 Pearson Education, Inc. Writing Ionic Formulas from Ionic Charges The group of ions that contains the lowest ratio of ions in an ionic compound is called a formula unit.

9. © 2014 Pearson Education, Inc. Learning Check Use charge balance to write the formula for lithium nitride, a compound containing Li + and N 3−.

10. © 2014 Pearson Education, Inc. Use charge balance to write the formula for lithium nitride, a compound containing Li + and N 3−. Solution

11. © 2014 Pearson Education, Inc. Learning Check Use charge balance to write the ionic formula of the compound containing Ba 2+ and Cl −.

12. © 2014 Pearson Education, Inc. Solution Use charge balance to write the ionic formula of the compound containing Ba 2+ and Cl −.

13. © 2014 Pearson Education, Inc. Learning Check Select the correct formula for each of the following ionic compounds: A.Li + and O 2− (1) LiO(2) Li 2 O(3) LiO 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

14. © 2014 Pearson Education, Inc. Solution Select the correct formula for each of the following ionic compounds: A.Li + and O 2− (2) Li 2 O B.Al 3+ and Cl − (1) AlCl 3 C.Mg 2+ and N 3− (3) Mg 3 N 2