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Chapter 10 Molecular Structure: Liquids and Solids

10.4

Electronegativity and Polarity

Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Electronegativity values• Indicate the attraction of an atom for shared

electrons. • Increases 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

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Some Electronegativity Values for Group A Elements

Low values

High values

Electronegativity increases

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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

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A polar covalent bond • Occurs between nonmetal atoms.• Is an unequal sharing of electrons.• Has a moderate electronegativity difference

(0.5 to 1.7).

Examples: Atoms Electronegativity Type of

Bond 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

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Comparing Nonpolar and Polar Covalent Bonds

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Ionic BondsAn ionic bond • Occurs between metal and nonmetal ions.• Is a result of electron transfer.• Has a large electronegativity difference (1.8 or more).

Examples: Atoms Electronegativity Type of Bond

Difference Cl-K 3.0 – 0.8 = 2.2 Ionic

N-Na 3.0 – 0.9 = 2.1 Ionic

S-Cs 2.5 – 0.7 = 1.8 Ionic

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Predicting Bond Types

Table 10.4

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Range of Bond Types

Table 10.5

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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

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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

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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 H—N—H dipole │

H dipoles do not cancel

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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

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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

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Learning Check

Identify each of the following molecules as

1) polar or 2) nonpolar. Explain.

A. PBr3

B. HBr

C. Br2

D. SiBr4

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Solution

Identify each of the following molecules as

1) polar or 2) nonpolar. Explain.

A. PBr3 1) 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