Chemistry 400; General Chemistry
Discussion: Chapter 11: Intermolecular Forces
Type of Force
Typical Energy
Example
Notes:
Bond:
Ionic Bond
≈500-5,000 kJ/mol
Between ions such as in
NaCl
Ions held together by
opposite charges
Covalent Bond
≈100-1,000 kJ/mol
Between atoms in the same
molecule that share
electrons
Bond comprised of shared
electrons
Ion-Ion Force
(another name for
an Ionic Bond)
Hydrogen “Bond”
≈500-5,000 kJ/mol
Between ions such as in
NaCl
Ions held together by
opposite charges
≈10-40 kJ/mol
NOT A REAL BOND!
Strong version of dipoledipole forces.
Dipole-Dipole
Force
≈4-20 k/mol
Between molecules with H–
F, H–O, or H–N bond & a
lone pair of electrons on an
O, N or F.
Between polar molecules
Dispersion Force
≈0.04-10 kJ/mol for
small molecules, can be
much larger for
polymers
IMF:
Between all atoms or
molecules
Molecule must have a
dipole to have dipoledipole forces.
All molecules/atoms have
dispersion forces.
Dispersion forces get
larger as the size of the
molecule gets larger.
1. What type of forces generally involve more energy, covalent bonds or IMF of covalent molecules?
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2. Are ionic bonds and ionic forces the same thing with two different names? (answer yes!)
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3. Arrange the following compounds in order of decreasing intermolecular ion-ion forces.
BaF2
LiF
NaCl
BaO
4. Arrange the following compounds in order of decreasing intermolecular ion-ion forces.
CsI
Al2S3
Fe2S3
FeS
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5. Which compound exhibits stronger dipole-dipole forces: HCl or HBr?
6. Which compound exhibits stronger dipole-dipole forces: CHF3 or CHBr3?
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A hydrogen bond is not a “bond” in the classical meaning of the term. It is an intermolecular force of attraction between 2 distinct
molecules.
Molecule #1 needs to have: A H atom covalently bonded to an O, N, or F atom.
Molecule #2 needs to have: A lone pair of electrons on an O, N, of F atom.
7. Can the following compounds form hydrogen bonds with another molecule of itself? If so, show two of the molecules (with their
Lewis Structures) and the formation of at least one hydrogen bond between them.
A. NH3
B. CH4
C. H2O
D. HF
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8. All of the following compounds can form at least one hydrogen bond to water. Show all of the possible hydrogen bonds between
the molecule and water (with their Lewis Structures).
OH
A.
NH2
B.
O
C.
O
||
D. CH3COH
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If we start a simulation with three atoms that are isolated.
As the atom on the right approaches the one in the middle, their charge clouds repel each other and begin to move to the opposite sides
of the atom.
This then leaves the two nuclei more exposed to each other and a temporary repulsive force is set up.
The center atom then gets repelled by the right atom and moves to the left.
The charge cloud from the center atom starts to influence the cloud on the left atom.
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This allows an induced dipole –induced dipole attractive force to be set up.
These attractive forces are very temporary and are constantly changing from one atom or molecule to the next.
Also, the more spread out or dispersed the atoms in a molecule, the greater the London Dispersion Forces.
(a)
(b)
Compound (b) has greater dispersion forces than compound (a).
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9. Rank the following substances from strongest to weakest intermolecular forces:
He
NH3
NF3
NaCl
10. Rank the following substances from strongest to weakest intermolecular forces:
HF
F2
FCl
11. Rank the following substances from strongest to weakest intermolecular forces:
NaCl
MgCl2
AlCl3
MgS
12. Rank the following from highest to lowest boiling point:
H 2O
NaF
F2
I2
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NaBr
13. Rank the following from highest to lowest boiling point:
He
Ne
Ar
Kr
14. Rank the following from highest to lowest boiling point:
MgBr2
NH3
CH4
Fe2S3
15. Which of the following has the higher boiling point? Why?
versus
16. Which of the following has the higher boiling point? Why?
versus
17. Which of the following has the higher boiling point? Why?
COOH
versus
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