1 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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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