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Wize University Chemistry Textbook > Intermolecular Forces and Physical Properties

Other Intermolecular Forces (more detailed)

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Types of Intermolecular Forces

Ion - Ion
  • Oppositely charged ions held together by electrostatic attraction
  • aka Ionic bonding (Ionic bonding is an intramolecular bond between a non-metal and a metal)
  • Strongest intermolecular force
Photo by Rhannosh / CC BY



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Ion - Dipole
  • Involves an ion interacting with a polar molecule (molecule with a net dipole)
  • A positively charged ion will interact with the δ– side of the polar molecule
  • A negatively charged ion will interact with the δ+ side of the polar molecule

Blank on top left: ion-ion interactions
Blank on bottom left: ionic bond
Black on top right: ion-dipole

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Hydrogen Bonding
  • Hydrogen bonded to N, O, or F is attracted to lone pairs of electrons on other N, O or F

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Dipole - Dipole

  • Interaction between two polar molecules
  • Opposite dipoles attract (δ– and δ+)


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Ion - Induced Dipole:
  • Ion causes a temporary dipole in non-polar species
  • In the example below, the positively charged ion makes the non-polar species shift its electrons towards the positive charge, creating an uneven charge distribution in the non-polar species


Dipole - Induced Dipole
  • Polar molecule causes a temporary dipole in non-polar species
  • Similar to ion-induced dipole, except that in dipole-induced dipole it is a polar molecule instead of an ion that induces a temporary dipole in the non-polar species
  • Weaker than ion-induced dipole forces


Induced Dipole - Induced Dipole
  • Molecules interact randomly and distort each other's electron clouds, causing temporary dipoles
  • Electrons randomly move around and at one point, more electrons may be on one side than the other in a non-polar molecule, creating a temporary dipole. That can happen with another non-polar molecule as well and the two can interact
  • We call this random movement of electrons polarizability
  • aka London dispersion forces (all molecules have this)

Intermolecular Forces

Intermolecular forces = forces between molecules



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Example: Recognizing Intermolecular Forces

Choose the strongest type of interaction two of the same molecule pictured to the left as Lewis structures, will have with one another


a) Ion-ion is not a choice here so the best option is ion-dipole (Na+ is the ion and HCOO- is the polar molecule)

b) London dispersion forces. This molecule is non-polar (no dipoles, no ions, no hydrogen bonding)

c) In the line diagram, 2 lone pairs are drawn on top of the oxygen atom, creating a polar molecule. The O is not bound to a H so hydrogen bonding is not possible. Dipole-dipole interactions are present in polar molecules.

d) Hydrogen bonding. This molecule is polar and has dipole-dipole forces but it also has hydrogen bonding, which is stronger. We can tell it has hydrogen bonding because the O is bound to a H.
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Example: Strongest Interaction Between Pairs of Molecules

Predict what the strongest type of interaction will be between the following pairs of molecules.

a) CH4 and H2O

Dipole-Induced dipole



b) NH3 and HF

This is a special case of dipole-dipole interactions called hydrogen bonding.



c) NaCl and H2O

Ion-Dipole (I-D).




d) H2 and Cl2

Induced Dipole-Induced Dipole (ID-ID) aka London dispersion forces


Practice: Ranking Intermolecular Interactions

Based on the three examples below, rank the strength of the intermolecular interaction from highest to lowest.

A) NH3 with NH3 B) CH4 with Ne C) Ca2+ with H2O

Practice: Intermolecular Forces

A student mixes HF with PCl3 at 0oC and forms a liquid mixture. What types of intermolecular forces are present between the two components of this liquid mixture, HF and PCl3?