Handout 11-1:
Ranking Molecular Properties Based On Intermolecular Forces
How To Determine Which
Intermolecular Force Is Present
The idea is to assign a molecule’s intermolecular forces to one or more of the categories in the table. Use these steps to help you.
 Draw the 3D Lewis dot structure of the molecule(s).
 Assign electronegativities to each atom.
o See the trend in the table?
H
2.1
Li
Be
B
C
N
O
F
Ne
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0
 Draw a dipole moment along each bond. Exaggerate the length of the arrow to indicate the magnitude. In other words, if there isn’t
any difference in electronegativity, there would be no dipole and therefore no arrow, while an electronegativity difference of 2-3
would indicate a large dipole and therefore be represented by a large arrow.
 Sum the vectors. Look for symmetry that cancels out vectors. DO NOT FALL INTO THE TRAP OF PERFORMING THIS STEP
WITHOUT DRAWING THE LEWIS DOT STRUCTURE FIRST!
Handout 1: Intermolecular Forces - Ranking Molecular Forces
Table of Intermolecular Forces
Energy (kJ/mol):
<1
5
10-40
Bond or Attraction:
LONDON FORCES
DIPOLE-DIPOLE
Synonyms:
 vander Waal’s
 instantaneous
dipole
 dispersion forces
 induced dipole
 permanent dipole
Identification Rules:
Examples:
Physical Properties:
400
intramolecular
Name:
Text Reference:
(Tro 3Ed)
Characteristics:
200
intermolecular
Chap 11, pg 433








non-polar
no net dipole
ΔEN = 0 OR
Δdipole = 0
Ar, N2, CH4,
lowest BP
lowest viscosity
high evaporation
low surface
tension
Chap 11, pg 435
 polar
 net dipole
 Δdipole / 0




NO, CH3Br
higher BP
higher viscosity
lower evaporation
higher surface
tension
HYDROGEN BONDING
IONIC BONDS
COVALENT BONDS
Chap 11, pg 437
Chap 9, pg 345
Ch 9, pg 349
 strongest of
intermolecular forces
 electronegative atom
 H attached to N, O, F
H2O, CH3OH, NH3
 highest BP
 highest viscosity
 lowest evaporation
 highest surface tension
 donates/accepts
electrons
 ΔEN = ~2-3
 metal/nonmetal
NaCl, CaO, Na3PO4
 solids
 high melting and
boiling points
 H bonding
Now ask yourself, “what can I do with this information!?”
 shares electrons
 ΔEN = ~0-1.5
 nonmetal/nonmetal
C-C, C=O, N≡N
 gases, liquids
 low melting and
boiling points