04/11/2010
Chapter 11 Intermolecular forces, liquids, and solids
Reading: Chapter 11, section 11.1-11.2, 11.8
Chapter 11 Intermolecular forces, liquids, and solids
11.1 A molecular comparison of gases, liquids and solids
The fundamental difference between states of matter is the distance between
particles.
As you read these sections ask yourself:
Why are intermolecular forces important?
incompressible
What are the main properties of liquids in contrast to gases
and solids?
gas
liquid
What kinds of interactions are the origins of intermolecular
forces?
solid
Why are intermolecular forces generally much weaker than
bonding forces?
How can you predict the presence of hydrogen bonding in a
compound?
What interactions exist to make a substance a solid?
What is the difference between molecular, ionic, metallic and
covalent?
Hydrogen bonding
11.2 Intermolecular forces
covalent bond
(strong)
intermolecular
attraction (weak)
H2O
Dipole-Dipole Interactions
H2Te
H2Se
H2S
SiH4
CH4
GeH4
SnH4
due to the increased surface area in n-pentane
London Dispersion Forces
momentarily polar
e
―
e
―
He atom
e
―
e
―
He atom 1
e
―
e
―
δ–
δ+
Ion-dipole forces
He atom 2
δ–
δ+
δ–
δ+
Ion-dipole interactions, are an important
force in solutions of ions.
cationdipole
n-pentane
bp 309 K
aniondipole
neopentane
bp 283 K
1
04/11/2010
Molecular Solids
interacting
molecules or ions
YES
are polar
molecules and ions
both present?
YES
are ions
involved?
NO
A) ionic bonding
e.g. NH4NO3
B) ion-dipole forces
e.g. NaCl in H2O
A>B>C>D>E
London dispersion
dipole-dipole
hydrogen bonding
11.8 Bonding in solids
Intermolecular forces: a summary
Consist of atoms or molecules held together by intermolecular forces.
are polar
molecules
involved?
NO
are H atoms
bonded to N, O or
F atoms?
NO
D) dipoledipole forces
YES
e.g. H2S, CH2Cl2
YES
high mp due to
efficient packing
E) dispersion forces
only (induced dipoles)
e.g. Ar(l), I2(s)
C) hydrogen bonding
e.g. H2O, NH3, HF
benzene
toluene
5
–95
43
80
111
182
NO
phenol
high mp & bp
due to hydrogen
bonding
high bp due to larger
intermolecular forces
van der Waals
forces
Covalent-Network Solids
Ionic Solids
Consist of atoms held together, in large networks or chains, with covalent bonds.
Consist of ions held together by ionic bonds (i.e. by electrostatic forces of attraction).
Cl
Cs
CsCl
S
Zn
ZnS
“zinc blende”
Ca
F
CaF2
“fluorite”
Metallic Solids
Consist entirely of metal atoms;
1.42 Å
not covalently bonded.
3.41 Å
2