6.5-6.6 electroneg polarmolec
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ElectromagTRANSCRIPT
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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
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Electronegativity
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
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Some Electronegativity Values for Group A Elements
Copyright 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
Low values
High values
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Nonpolar Covalent Bonds
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 BondDifference
N-N 3.0 - 3.0 = 0.0 Nonpolar covalent
Cl-Br 3.0 - 2.8 = 0.2 Nonpolar covalent
H-Si2.1 - 1.8 = 0.3 Nonpolar covalent
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Polar Covalent Bonds
A polar covalent bond,
Occurs between nonmetals atoms
Is an unequal sharing of electrons
Has a moderate electronegativity difference (0.5 to 1.7)
Examples:
Atoms ElectronegativityType of Bond Difference
O-Cl 3.5 - 3.0 = 0.5Polar covalent
Cl-C 3.0 - 2.5 = 0.5Polar covalent
O-S 3.5 - 2.5 = 1.0Polar covalent
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Comparing Nonpolar and Polar Covalent Bonds
Copyright 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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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)
Examples:
Atoms ElectronegativityType of Bond Difference
Cl-K 3.0 0.8 = 2.2Ionic
N-Na 3.0 0.9 = 2.1Ionic
S-Cs2.5 0.7= 1.8Ionic
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Range of Bond Types
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Predicting Bond Types
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Learning Check
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
B. N-O
C. Cl-Cl
D. H-Cl
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Solution
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-N2.2ionic (I)
B. N-O0.5 polar covalent (P)
C. Cl-Cl0.0nonpolar covalent (NP)
D. H-Cl0.9polar covalent (P)
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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
+ -
HCl ClNCl
dipole
Cl
dipoles do not cancel
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Nonpolar Molecules
A nonpolar molecule,
Contains nonpolar bonds
ClCl HH
Or has a symmetrical arrangement of polar bonds
O=C=O Cl
ClCCl
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
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HO: 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. PBr31) pyramidal; dipoles dont cancel; polar
B. HBr1) linear; one polar bond (dipole); polar
C. Br22) linear; nonpolar bond; nonpolar
D. SiBr42) tetrahedral; dipoles cancel; nonpolar