1 chapter 6 molecules and covalent compounds 6.5 electronegativity and bond polarity 6.6 polarity of...

1

Chapter 6 Molecules and Covalent Compounds

6.5

Electronegativity and Bond Polarity

6.6

Polarity of Molecules

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

2

Electronegativity values:• Indicate the attraction of an atom for shared

electrons • Increase from left to right going across a period on

the periodic table• Is high for the nonmetals with fluorine as the

highest • Is low for the metals

Electronegativity

3

Some Electronegativity Values for Group A Elements


Low values

High values

4

A nonpolar covalent bond, • Occurs between nonmetals• Is an equal or almost equal sharing of electrons• Has almost no electronegativity difference (0.0 to 0.4)

Examples: Atoms Electronegativity Type of Bond

DifferenceN-N 3.0 - 3.0 = 0.0 Nonpolar covalent

Cl-Br 3.0 - 2.8 = 0.2 Nonpolar covalentH-Si 2.1 - 1.8 = 0.3 Nonpolar covalent

Nonpolar Covalent Bonds

5

A polar covalent bond, • Occurs between nonmetals atoms• Is an unequal sharing of electrons• Has a moderate electronegativity difference (0.5 to 1.7)


DifferenceO-Cl 3.5 - 3.0 = 0.5 Polar covalentCl-C 3.0 - 2.5 = 0.5 Polar covalentO-S 3.5 - 2.5 = 1.0 Polar covalent

Polar Covalent Bonds

6

Comparing Nonpolar and Polar Covalent Bonds


7

Ionic Bonds

An ionic bond, • Occurs between metal and nonmetals ions• Is a results of electron transfer• Has a large electronegativity difference (1.8 or more)


Difference Cl-K 3.0 – 0.8 = 2.2 IonicN-Na 3.0 – 0.9 = 2.1 IonicS-Cs 2.5 – 0.7 = 1.8 Ionic

8

Range of Bond Types

9

Predicting Bond Types

10

Use the electronegativity difference to identify the type of bond between the following as:nonpolar covalent (NP), polar covalent (P), or

ionic (I).

A. K-NB. N-OC. Cl-ClD. H-Cl

Learning Check

11

Use the electronegativity difference to identify the type of bond between the following as:nonpolar covalent (NP), polar covalent (P), or

ionic (I).

A. K-N 2.2 ionic (I) B. N-O 0.5 polar covalent (P)

C. Cl-Cl 0.0 nonpolar covalent (NP) D. H-Cl 0.9 polar covalent (P)

Solution

12

Polar Molecules

A polar molecule, • Contains polar bonds

• Has a separation of positive and negative charge called a dipole indicated with + and

• Has dipoles that do not cancel

+ - • •

H–Cl Cl—N—Cl dipole

Cl dipoles do not

cancel

13

Nonpolar Molecules

A nonpolar molecule, • Contains nonpolar bonds

Cl–Cl H–H

• Or has a symmetrical arrangement of polar bonds

O=C=O Cl

Cl–C–Cl

Cl

dipoles cancel

14

Determining Molecular Polarity

STEP 1 Write the electron-dot formula.

STEP 2 Determine the polarity of the bonds.

STEP 3 Determine if any dipoles cancel or not.

Example: H2O

. .

H─O: H2O is polar

│

H dipoles do not cancel

15

Learning Check

Identify each of the following molecules as:

1) polar or 2) nonpolar. Explain.

A. PBr3

B. HBr

C. Br2

D. SiBr4

16

Solution

Identify each of the following molecules as:

1) polar or 2) nonpolar. Explain.

A. PBr31) pyramidal; dipoles don’t cancel; polar

B. HBr 1) linear; one polar bond (dipole); polar

C. Br2 2) linear; nonpolar bond; nonpolar

D. SiBr4 2) tetrahedral; dipoles cancel; nonpolar

1 chapter 6 molecules and covalent compounds 6.5 electronegativity and bond polarity 6.6 polarity of...

Documents