Intermolecular Forces
O
O
O
O
H
H
H
H
H
H
H
H
O
O
O
O
H
H
H
H
H
H
H
H
O
O
O
O
H
H
H
H
H
H
H
H
(given in increasing strength)
• Explain the types of intermolecular forces
possible.
Include: Dispersion, Dipole, Hydrogen-bonding
• Compare and contrast polar, non-polar, and
ionic bonding in terms of IMFs
Include: examples of each bonding type.
Additional KEY Terms
Dipole
1. London dispersion force
(Weakest)
(O2NON-POLAR
, Cl2, CH4, C2Hmolecules.
)
Occurs between
8
• Atoms of a NP molecule equally share bonding e-.
• normally no overall charge.
H
H
C
H
H
At any given time, e- in a molecule are unevenly
distributed – e- move.
Causes temporary dipoles (charged regions) to
form, which leads to attraction between molecules.
δ+
H
H
δ
-
C
H
H
F2
F
+
F
F
F2
F
+
δ+
+
δ-
non - polar molecules
+
CH4
CH4
H
H
H
C
H
H
δ+
H
δ-
C
H
H
temporary
dipole
non - polar molecules
2. Dipole-Dipole
One atom of a molecule pulls the shared electrons
closer than the other (unequal sharing).
Causes permanent negative and positive dipoles.
The polar ends attract other polar molecules.
δCl
δ+
H
δ-
δ
-
δ+
δ
δ-
+
H
δ+
Cl
H
Cl
permanent
dipole
polar molecules
3. Hydrogen bond
(special dipole-dipole force)
• Very strong force.
• Any substance containing hydrogen bonded
directly to O, N, or F.
• O, N and F pull extremely hard on the bonding
electrons (VERY unequal sharing) - large dipoles.
δ-
δ+
H
O
H
H
δ
H
H
δ
+
N
H
δ- O
+
H
H
H
N
H
-
δ+
H
H
O
δ
H
H
δ+
H
H
δ+
N
H
H
polar molecules
4. Strong ionic attraction
Positive and negatively charged IONS held
together by electrostatic (attraction) forces.
These electrostatic forces are extremely strong,
giving ionic compounds very large melting and
boiling points.
• Electrostatic Attraction
• Permanent - strongest
• MgBr2 or Ca(NO3)2
• Dipole or H-bonds
• Permanent
• HCl or H2O
• Dispersion
Dispersion Forces
Forces
• Temporary - weak
• CH4 or Cl2
The Special Case for Water
Hydrogen-bonding holds water molecules
together strongly.
Responsible for the higher
than expected melting point
and boiling point.
Because of H - bonding, ice forms unique crystal
shape (six-sided), having an area greater than that
liquid water.
Ice is less dense than water...most solids are more
dense than their respective liquids.
CAN YOU / HAVE YOU?
• Explain the types of intermolecular forces
possible.
Include: Dispersion, Dipole, Hydrogen-bonding
• Compare and contrast polar, non-polar, and
ionic bonding in terms of IMFs
Include: examples of each.
Additional KEY Terms
Dipole