2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Ionic and Covalent Bonding Objectives Explain why atoms sometimes join to form bonds. Explain why some atoms transfer their valence electrons to form ionic bonds, while other atoms share valence electrons to form different bonds. Differentiate between ionic, covalent, and metallic bonds. Compare the properties of substances with different types of bonds. Chapter 5

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Ionic and Covalent Bonding Bellringer You have already learned that atoms are the most stable when their outer energy levels are filled. One way to model atoms is using diagrams, such as the flowers shown below. To represent a stable atom, the flower diagram must have eight petals around the center. Assume that each petal represents an electron with a negative charge and that the centers of the flowers represent positively charged nuclei. Chapter 5

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Ionic and Covalent Bonding Bellringer, continued 1. What had to happen to the flower diagrams so that they could represent stable atoms? 2. What happened to the charge on each of the flower diagrams? 3. What do you think will happen to the oppositely charged ions represented by the flower diagrams? Chapter 5

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Ionic and Covalent Bonding What Holds Bonded Atoms Together? Bonded atoms usually have a stable electron configuration. Example: As shown at right, when two hydrogen atoms bond, their electron clouds overlap. The resulting hydrogen molecule has an electronic structure similar to the noble gas helium. Chapter 5

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Ionic and Covalent Bonding What Holds Bonded Atoms Together? continued Bonds can bend and stretch without breaking. Although a “bar” is sometimes used to represent a bond between two atoms, chemical bonds behave more like flexible springs. Chapter 5

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Ionic and Covalent Bonding Ionic Bonds Ionic bonds are formed between oppositely charged ions. As shown at right, ionic compounds are in the form of networks of formula units, not molecules. Chapter 5 When melted or dissolved in water, ionic compounds conduct electricity.

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Ionic Bonding Section 2 Ionic and Covalent Bonding Chapter 5

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Ionic and Covalent Bonding Metallic Bonds A metallic bond is a bond formed by the attraction between positively charged metal ions and the electrons around them. Electrons move freely between metal atoms. This model explains why metals: conduct electricity conduct heat are flexible Chapter 5

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Metallic Bonding Section 2 Ionic and Covalent Bonding Chapter 5

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Ionic and Covalent Bonding Covalent Bonds A covalent bond is a bond formed when atoms share one or more pairs of electrons. Covalent compounds can be solids, liquids, or gases. Bonds in which atoms share electrons equally are called nonpolar covalent bonds, as shown below. Chapter 5

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Ionic and Covalent Bonding Covalent Bonds, continued Atoms do not always share electrons equally. An unequal sharing of electrons forms a polar covalent bond. Atoms may share more than one pair of electrons. Chapter 5

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Comparing Polar and Nonpolar Covalent Bonds Section 2 Ionic and Covalent Bonding Chapter 5

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Ionic and Covalent Bonding Polyatomic Ions A polyatomic ion is an ion made of two or more atoms. There are many common polyatomic ions. Some are shown at right. Chapter 5 Parentheses group the atoms of a polyatomic ion. Example: the chemical formula for ammonium sulfate is written as (NH 4 ) 2 SO 4, not N 2 H 8 SO 4.

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Ionic and Covalent Bonding Polyatomic Ions, continued Some polyatomic anion names relate to their oxygen content. An -ate ending is used to name an ion with more oxygen. Examples: sulfate (SO 4 2– ), nitrate (NO 3 – ), chlorate (ClO 3 – ) An -ite ending is used to name an ion with less oxygen. Examples: sulfite (SO 3 2– ), nitrite (NO 2 – ), chlorite (ClO 2 – ) Chapter 5

16. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Comparing Ionic and Molecular Compounds Section 2 Ionic and Covalent Bonding Chapter 5