Understanding Covalent Bonds and Molecular Compounds

1. Ch. 5 Atoms and BondingSection 3: Covalent Bonds Objectives – I will state what holds covalently bonded atoms together, identify the properties of molecular compounds, and explain how unequal sharing of electrons occurs and how it affects molecules.

2. A. How Covalent Bonds Form • Covalent bond is a chemical bond formed when two atoms share electrons. • Covalent bonds usually form between atoms of nonmetals. • Ionic bonds usually form when a metal combines with a nonmetal.

3. a. Electron Sharing • Copy figure 14 on page 167 in P.S. book 1. The force that holds atoms together in a covalent bond is the attraction of each atom’s nucleus for the shared pair of electrons. 2. A molecule is a neutral group of atoms joined by covalent bonds

4. b. How Many Bonds? • Explain figure 15 on the white board page 167 in P.S. Book • Copy figure 15 page 167 in P.S. book

5. c. Double Bonds and Triple Bonds 1. Double bond is a chemical bond formed when atoms share two pairs of electrons. 2. Triple bond is a chemical bond formed when atoms share three pairs of electrons. • Copy figure 16 in P.S. book page 168

6. B. Molecular Compounds • A molecular compound is a compound that is composed of molecules. • The molecules of a molecular compound contain atoms that are covalently bonded. • Compared to ionic compounds, molecular compounds generally have lower melting points and boiling points, and they do not conduct electricity when dissolved in water.

7. a. Low Melting Points and Boiling Points 1. In molecular solids, forces hold the molecules close to one another, 2. But the two forces between molecules are much weaker than the forces between ions in an ionic solid. 3. Compared with ionic solids, less heat must be added to molecular solids to separate the molecules and change the solid to a liquid. • Let’s do Analyzing Data on page 169 in P.S. Book

8. b. Poor Conductivity 1. Most molecular compounds do not conduct electric current. 2. Materials such as plastic and rubber are used to insulate wires because these materials are composed of molecular substances.

9. C. Unequal Sharing of Electron • Atoms of some elements pull more strongly on shared electrons than do atoms of other elements. As a result, the electrons are pulled more toward one atom, causing the bonded atoms to have slight electrical charges.

10. a. Polar Bonds and Nonpolar Bonds 1. Polar bond is a covalent bond in which electrons are shared unequally. 2. Nonpolar bond is a covalent bond in which electrons are shared equally. • Copy figure 17 on page 170 in P.S. book

11. b. Polar Bonds in Molecules • Copy figure 18 on page 170 in P.S. Book 1. The two oxygen atoms pull with equal strength in opposite directions. In a sense, the attractions cancel out, and the molecule is nonpolar. 2. In contrast, other molecules that have polar covalent bonds are themselves polar. • Example is a water molecule. The two hydrogen atoms are at one end of the molecule, while the oxygen atom is at the other end. Mickey Mouse ears.

12. c. Attractions Between Molecules 1. The negatively charged oxygen ends of the polar water molecules attract the positively charged hydrogen ends of nearby water molecules. 2. These attractions pull water molecules toward each other. 3. The properties of polar and nonpolar compounds differ because of differences in attractions between their molecules.

13. 4. For example; water and oil don’t mix. The molecules in oil are nonpolar, and nonpolar molecules have little attraction for polar water molecules. 5. Adding detergent helped oil and water mixed because on end of a detergent molecule has nonpolar covalent bonds while the other end includes an ionic bond. The detergent’s nonpolar end mixes easily with oil while the charged ionic end is attracted to polar water molecules.