When
Intermolecular Forces
Rule
PGCC CHM 2000 Sinex
Comparison of properties for the states of matter
Property
Solid
Liquid
Gas
Volume
Shape
definite
definite
definite
indefinite
indefinite
indefinite
Relative density
Compressibility
high
low-none
~1 g/mL
low-none
very low
very high
Fluidity/mobility
Particle packing
Diffusion rate
Motion of
particles
no
close
very slow
vibrations
only
Forces between
particles
IMF’s or
bonding
yes
yes
close
far apart
medium
fast
translation translation
rotation
rotation
IMF’s
only
none if
ideal gas
The liquid state of matter
Molecules are closely packed
but
free to move about randomly.
There must be a force of attraction between the molecules.
As molecules start to vaporize
Molecules are great
distances apart
in gaseous state
but
free to move about
randomly.
What about
in solids?
Click here for a simulation of the states of matter
Force-distance relationship
For the Fattraction proportional to 1/distance
molecules in contact with each other
Relative attractive force
1
0.8
0.6
0.4
0.2
0
0
1
2
3
4
5
6
7
8
Relative molecular distance
9
10
Force-distance relationship
Relative attractive force
1
1
0.8
0.6
0.4
0.2
0
0
1
2
3
4
5
6
7
8
Relative molecular distance
9
10
Force-distance relationship
Relative attractive force
1
2
0.8
0.6
0.4
0.2
0
0
1
2
3
4
5
6
7
8
Relative molecular distance
9
10
Force-distance relationship
Relative attractive force
1
3
0.8
0.6
0.4
0.2
0
0
1
2
3
4
5
6
7
8
Relative molecular distance
9
10
Force-distance relationship
Relative attractive force
1
4
0.8
0.6
0.4
0.2
0
0
1
2
3
4
5
6
7
8
Relative molecular distance
9
10
Force-distance relationship
Relative attractive force
1
5
0.8
0.6
Less than 20% the strength
at 5 molecular distances
0.4
0.2
0
0
1
2
3
4
5
6
7
8
Relative molecular distance
9
10
Increasing strengths of IMF
The strength of IMF’s
•
•
•
•
•
•
•
H-bonding (fixed distance ~200 pm)
Ion-ion (1/r)
Ion-dipole (1/r2)
Inverse
3
Dipole-dipole (1/r )
functions
of
Ion-induced dipole (1/r4)
distance
6
Dipole-induced dipole (1/r )
to various
powers
Induced dipole-induced dipole
(1/r6)
How do the other functions behave compared to 1/r?
Click here for an interactive Excel spreadsheet to explore
Hydrogen bonding in water
O-H 96 pm
covalent bond
… H 186 pm
O
Base Pairs in DNA: H-bonding
AT pair
Why not
here?
GC pair
What holds the iodine molecules
together in solid iodine?
272 pm for I2 covalent bond
427 pm between two molecules in crystalline structure
About half an iodine atom space between molecules
Graphite
weak intermolecular
forces between layers
(van der Waals forces)
graphene
C-C bond distance: 142 pm
C to C distance between layers – 336 pm