7-2 OBJECTIVES Define covalent bond. Give examples of substances that contain covalent bonds. Distinguish between a molecular formula, an empirical formula, and a structural formula. Describe covalent bonds in terms of Lewis dot structures and the octet rule. Explain the difference between single, double, and triple covalent bonds. Compare and contrast polar and nonpolar covalent bonds. PPowell 05

Covalent Bond Formed when two atoms share a pair of electrons How are covalent bonds different from ionic bonds? Molecule: two or more atoms bonded covalently OBJ: Define covalent bond. OBJ: Give examples of substances that contain covalent bonds.

Molecules and Their Formulas Molecular formula: tells how many atoms are in one molecule of the compound molecular formula for table sugar: C 12 H 22 O 11 Does NOT show you which atoms are bonded to which This means you can have the same molecular formula for different compounds OBJ: Distinguish between a molecular formula and a structural formula.

Structural Formulas Show ratio of different kinds of atoms in a compound Show which atoms in a compound are bonded to each other F Shared electrons OBJ: Distinguish between a molecular formula and a structural formula.

Molecular vs. Empirical Formulas Empirical formulas give you the simplest ratio of the atoms in the compound Ex: glucose –Mol. formula: C 6 H 12 O 6 –Emp. formula: CH 2 O This means different compounds can share the same empirical formula Ex: lactose (a type of sugar in milk) –Mol. formula: C 3 H 6 O 3 –Emp. formula: CH 2 O OBJ: Distinguish between a molecular formula and an empirical formula.

Describing Covalent Bonds Formation of covalent bonds allows atoms to satisfy the octet rule F Covalent Bond FF Fluorine atoms have 7 valence electrons Two F atoms each share an e- with the other in a covalent bond Now each F atom has a complete octet OBJ: Describe covalent bonds in terms of Lewis dot structures and the octet rule.

Describing Covalent Bonds When drawing Lewis structures, use a dash to represent a covalent bond: This is a single bond But atoms can share more than one pair of electrons… F becomes F OBJ: Describe covalent bonds in terms of Lewis dot structures and the octet rule.

Double and Triple Bonds Double covalent bond: made up of two pairs of shared e- (one pair per bond) Triple covalent bond: made up of three pairs of shared e- (one pair per bond) OBJ: Explain the difference between single, double, and triple covalent bonds.

Drawing Lewis Dot Structures For Molecules 1.Add up the valence e- from all the atoms 2.Write the symbols for the atoms to show which atoms are attached to which, and connect them with a single bond 3.Complete the octets of the atoms bonded to the central atom 4.Place any leftover electrons on the central atom, even if it results in more than an octet 5.If there are not enough electrons to give the central atom an octet, try multiple bonds OBJ: Describe covalent bonds in terms of Lewis dot structures and the octet rule.

Molecular Formula: H 2 CO H H C O COH H COH H valence e- (check the dot diagrams for yourself) 2. Write symbols, connect with single bonds 2a. Notice that C needs 2 e- to make the octet, and O will need 6 e- BUT you only have 6 e- left e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- 3. Use the remaining e- to complete the octets To satisfy the octet rule for both O and C, there must be a double bond. COH H OBJ: Explain the difference between single, double, and triple covalent bonds.

Exceptions to the Octet Rule 1.Atoms with less than an octet –Example: Boron FF F B OBJ: Describe covalent bonds in terms of Lewis dot structures and the octet rule.

2.Atoms with more than an octet -Example: Sulfur Exceptions to the Octet Rule OBJ: Describe covalent bonds in terms of Lewis dot structures and the octet rule. SFF FF Extra e- fill the 3d orbitals of atoms that fall into this category

3. Atoms with an odd number of electrons –Example: Nitrogen Exceptions to the Octet Rule NON + O OBJ: Describe covalent bonds in terms of Lewis dot structures and the octet rule.

Properties of Covalent Bonds Polar covalent bond: (aka polar bond) a bond between two atoms with different electronegativities –Uneven sharing causes the more electronegative atom to be slightly negative in charge –The less electronegative atom will be slightly positive in charge OBJ: Compare and contrast polar and nonpolar covalent bonds.

More About Polar Bonds Figure 7-20, p. 242—draw it! Water has polar bonds Slight charges are called partial charges Partial charges symbolized with Greek letter delta (  ) Arrows can also be used to show the uneven sharing of electrons—point toward more electronegative atom, crossed at the other end OBJ: Compare and contrast polar and nonpolar covalent bonds.

Nonpolar covalent bonds: (aka nonpolar bonds) a bond between two atoms of similar or equal electronegativities Examples: H 2, N 2, O 2 Properties of Covalent Bonds OBJ: Compare and contrast polar and nonpolar covalent bonds.

Can you now meet the 7-2 OBJECTIVES? Define covalent bond. Give examples of substances that contain covalent bonds. Distinguish between a molecular formula, an empirical formula, and a structural formula. Describe covalent bonds in terms of Lewis dot structures and the octet rule. Explain the difference between single, double, and triple covalent bonds. Compare and contrast polar and nonpolar covalent bonds.