1. Chemical Bonding II: Covalent Bonds

2. Review Metals and nonmetals react to form ionic bonds. Metals and nonmetals react to form ionic bonds. With ionic bonds, electrons are transferred. With ionic bonds, electrons are transferred. The resulting ions have noble-gas configurations. The resulting ions have noble-gas configurations. Ionic compounds are written as formula units: ex. NaCl. Ionic compounds are written as formula units: ex. NaCl.

3. CharacteristicsIonic BondingCovalent Bonding FormationMetal + nonmetalNonmetal + nonmetal How is it formed?Electron transferElectron sharing Bond strengthStrongWeak ExamplesSalt, Epsom saltsSugar, alcohol NomenclatureMetal name + nonmetal name + -ide suffix Example: Aluminum nitride Use of numeric prefixes; first element first, second element second + -ide suffix; prefix on both elements based on the number of atoms; prefix –mono is NOT used on the first element. Example: Carbon Dioxide; one carbon, two oxygens

4. The Covalent Bond Atoms share electrons to achieve a stable octet. The bond that forms from shared electrons is a covalent bond. Atoms share electrons to achieve a stable octet. The bond that forms from shared electrons is a covalent bond. Covalent bonding occurs when elements are fairly close to one another on the periodic table. Nonmetals form covalent bonds. This would be groups 14-17. Covalent bonding occurs when elements are fairly close to one another on the periodic table. Nonmetals form covalent bonds. This would be groups 14-17. (video #1) (video #1)

5. Covalent bonds form molecules. Carbohydrates, simple sugars, proteins, fats, and DNA are covalently bonded molecules. Covalent bonds form molecules. Carbohydrates, simple sugars, proteins, fats, and DNA are covalently bonded molecules. Diatoms are atoms that are sharing electrons to achieve a stable octet. They bond with themselves. There are seven diatomic molecules. Diatoms are atoms that are sharing electrons to achieve a stable octet. They bond with themselves. There are seven diatomic molecules.

7. Diatomic Molecules Hydrogen: H 2; shares one pair of electrons Hydrogen: H 2; shares one pair of electrons Oxygen: O 2; shares two pairs Oxygen: O 2; shares two pairs Nitrogen: N 2; shares three pairs Nitrogen: N 2; shares three pairs Iodine: I 2; shares one pair Iodine: I 2; shares one pair Bromine: Br 2; shares one pair Bromine: Br 2; shares one pair Fluorine: F 2; shares one pair Fluorine: F 2; shares one pair Chlorine: Cl 2; shares one pair Chlorine: Cl 2; shares one pair

8. Unshared pairs of electrons are called lone pairs. Unshared pairs of electrons are called lone pairs. When a single pair of electrons is shared, a single covalent bond forms. Hydrogen and group 17 elements form SCBs. When a single pair of electrons is shared, a single covalent bond forms. Hydrogen and group 17 elements form SCBs.

9. When two pairs are shared, a double covalent bond forms. Group 16 elements form DCBs. When two pairs are shared, a double covalent bond forms. Group 16 elements form DCBs. When three pairs are shared, a triple covalent bond forms. Group 15 elements form TCBs. When three pairs are shared, a triple covalent bond forms. Group 15 elements form TCBs.

10. A triple bond has a shorter bond length than a double bond, and a double bond has a shorter length than a single bond. A triple bond has a shorter bond length than a double bond, and a double bond has a shorter length than a single bond. The shorter the bond length, the stronger the bond. The shorter the bond length, the stronger the bond. Single bonds, therefore, are weaker than double bonds, and double bonds are weaker than triple bonds. Single bonds, therefore, are weaker than double bonds, and double bonds are weaker than triple bonds.

11. Energy is released when a covalent bond forms, so energy must be added to break the bonds in a molecule. Energy is released when a covalent bond forms, so energy must be added to break the bonds in a molecule. The amount of energy required to break bonds is called bond dissociation energy, which is always positive. The amount of energy required to break bonds is called bond dissociation energy, which is always positive.

12. Endothermic reactions occur when energy is absorbed to break the bonds in the reactants. Exothermic reactions occur when energy is released and forms new bonds. Endothermic reactions occur when energy is absorbed to break the bonds in the reactants. Exothermic reactions occur when energy is released and forms new bonds.

13. Review What is a covalent bond? How does it differ from an ionic bond? What is a covalent bond? How does it differ from an ionic bond? What is a single covalent bond and how does it form? What family forms SCBs? What is a single covalent bond and how does it form? What family forms SCBs? Why do multiple bonds form? What families form MCBs? Why do multiple bonds form? What families form MCBs? How is bond length related to bond disassociation energy? How is bond length related to bond disassociation energy?