1
Part 08Intermolecular Forces
of Attraction
2
1. IMFAIntermolecular forces of attraction are any attraction that exists in BETWEEN two or more molecules.They are NOT bonds.
3
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.
4
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
5
Example:Diagram the London forces between two fluorine molecules and between two iodine molecules.Indicate which substance has the greater London forces.
6
F F
F F
+
+
-
-
London Forces
I I+
+
-
-
London Forces
I I
F2 18 electrons I2 126 electronsGreater LF
7
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.
8
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.
9
H Cl+-+
-
HCl+-
- +
EN = 1.4
DPDP
H Br+-+
-
HBr+-
- +
EN = 0.7
DPDP
More PolarStronger DPDP
10
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.
11
H F+-+
-
HF+-
- +
EN = 1.9VERY Polar Bonds
Hydrogen BondingHydrogen has FON in BOTH molecules.
HB
12
+-H O
H
-
+
+-H O
H
-
+
EN = 1.4Polar Bonds
HB
Hydrogen BondingHydrogen has FONin BOTH molecules.
13
+-
HN
H
H
-
+
EN = 0.9Polar Bonds
+-
HN
HH
-
+
HB
Hydrogen BondingHydrogen has FONin BOTH molecules.
14
p. 781.
BrBrNonpolar MoleculeLondon Forces
15
2.
H S
H Nonpolar MoleculeLondon Forces
16
3.
H P
H
H
Nonpolar MoleculeLondon Forces
17
4.
H Ge
H
H
H
Nonpolar MoleculeLondon Forces
18
5. Polar Molecule
Dipole-Dipole
Cl S
Cl+-
+
-
19
1.
Page 82
Se C Se
Nonpolar MoleculeLondon Forces
20
2.
AsCl
ClCl
Cl
Cl
+-
Nonpolar MoleculeLondon Forces
21
3.
B
I
II
+
-
Nonpolar MoleculeLondon Forces
22
4.
N O+ -
+
-
Polar MoleculeDipole-Dipole
23
5.
F Rn F+ -
Nonpolar MoleculeLondon Forces
24
p. 86
1. FBr + -
+
-
Polar MoleculeDipole-Dipole
25
2.
B
Br
BrBr
+
-
Nonpolar MoleculeLondon Forces
26
3.
Ge ClCl
Cl
Cl
+ -
Nonpolar MoleculeLondon Forces
27
Nonpolar MoleculeLondon Forces
4.
AsBr
BrBr
Br
Br
+-
28
Nonpolar MoleculeLondon Forces
5.
SF
F
FF
FF
-
+
29
Nonpolar MoleculeLondon Forces
6.
Se P
Se