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Part 08Intermolecular Forces

of Attraction

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1. IMFAIntermolecular forces of attraction are any attraction that exists in BETWEEN two or more molecules.They are NOT bonds.

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2. Types of IMFAa. London Dispersion Forces

Weak forces of attraction that exist between two or more nonpolar molecules.

Rule: The more electrons in the nonpolar molecule, the stronger the London forces.

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C H

H

H

H

+ -CH

H

H

H

+-

When the molecules are close, their electron clouds experience a momentary shift of electrons producing an instantaneous induced dipole.

LF

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Example:Diagram the London forces between two fluorine molecules and between two iodine molecules.Indicate which substance has the greater London forces.

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F F

F F

+

+

-

-

London Forces

I I+

+

-

-

London Forces

I I

F2 18 electrons I2 126 electronsGreater LF

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b. Dipole-Dipole AttractionsStronger forces of

attraction that exist between two or more polar molecules.

Rule: The more polar the molecule, the stronger the dipole-dipole attractions.

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Example:Diagram the London forces between two hydrogen chloride molecules and between two hydrogen bromide molecules.Indicate which substance has the greater dipole-dipole attractions.

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H Cl+-+

-

HCl+-

- +

EN = 1.4

DPDP

H Br+-+

-

HBr+-

- +

EN = 0.7

DPDP

More PolarStronger DPDP

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c. Hydrogen BondingVery strong force of

attraction between a hydrogen bonded to a fluorine, oxygen or nitrogen in one molecule for a fluorine, oxygen or nitrogen bonded to a hydrogen in another molecule.

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H F+-+

-

HF+-

- +

EN = 1.9VERY Polar Bonds

Hydrogen BondingHydrogen has FON in BOTH molecules.

HB

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+-H O

H

-

+

+-H O

H

-

+

EN = 1.4Polar Bonds

HB

Hydrogen BondingHydrogen has FONin BOTH molecules.

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+-

HN

H

H

-

+

EN = 0.9Polar Bonds

+-

HN

HH

-

+

HB

Hydrogen BondingHydrogen has FONin BOTH molecules.

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p. 781.

BrBrNonpolar MoleculeLondon Forces

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2.

H S

H Nonpolar MoleculeLondon Forces

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3.

H P

H

H

Nonpolar MoleculeLondon Forces

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4.

H Ge

H

H

H

Nonpolar MoleculeLondon Forces

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5. Polar Molecule

Dipole-Dipole

Cl S

Cl+-

+

-

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1.

Page 82

Se C Se

Nonpolar MoleculeLondon Forces

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2.

AsCl

ClCl

Cl

Cl

+-

Nonpolar MoleculeLondon Forces

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3.

B

I

II

+

-

Nonpolar MoleculeLondon Forces

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4.

N O+ -

+

-

Polar MoleculeDipole-Dipole

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5.

F Rn F+ -

Nonpolar MoleculeLondon Forces

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p. 86

1. FBr + -

+

-

Polar MoleculeDipole-Dipole

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2.

B

Br

BrBr

+

-

Nonpolar MoleculeLondon Forces

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3.

Ge ClCl

Cl

Cl

+ -

Nonpolar MoleculeLondon Forces

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Nonpolar MoleculeLondon Forces

4.

AsBr

BrBr

Br

Br

+-

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Nonpolar MoleculeLondon Forces

5.

SF

F

FF

FF

-

+

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Nonpolar MoleculeLondon Forces

6.

Se P

Se