Most of us know the three states of matter.
But when discussing Intermolecular Forces, we're only concerned with the 2 condensed states of matter - liquids and solids.
The Three States of Matter
- Gases - most compressible; the least dense
- Solids - least compressible; most dense
In this series of blog posts, we'll focus on the condensed states:
➞ liquids and solids...
Liquids and Solids
We know that the molecules of a liquid or solid are composed of atoms held together by "intramolecular forces" called bonds.
But individual molecules are aggregated together in a large sample (i.e. glass of water = billions upon billions of H2O molecules) by attractive forces called "intermolecular forces."
So... What are these "intermolecular forces," eh?
What are Intermolecular Forces ?
Intermolecular Forces (IMF's) = forces that cause the aggregation of components of a substance to form a liquid or solid.
Intermolecular Forces are much weaker than bonds (intramolecular forces).
For example, boiling H2O causes individual molecules to:
As mentioned above, heat supplies enough energy to break the intermolecular forces holding the H2O(l) molecules together.
But the bonds themselves ( H—O—H ) are not broken.
➞ Intermolecular Forces occur between molecules.
➞ Intramolecular Forces (bonds) occur within molecules.
Types of Intermolecular Forces
It's quite possible you've been told there are 3 types of intermolecular forces:
- London Dispersion Forces (LDF, or Dispersion Forces)
- Dipole-Dipole Forces (Dipole Forces)
- Hydrogen Bonding (H-Bonds)
And this is "sort of" true.
Hydrogen Bonding is actually a special (stronger) subgroup within the Dipole-Dipole Forces group.
Two Types of Intermolecular Forces
1. Dipole-Dipole Forces = only occur between polar molecules.
2. London Dispersion Forces = occur between all types of molecules, but these are the only forces holding nonpolar molecules and noble-gas atoms together.
London Dispersion Forces are also called:
➞ LDF, or
➞ Dispersion Forces, or
➞ van der Waals Forces.
In my next blog post covering SECTION 10 - Liquids, Solids, and Intermolecular Forces,
We'll take a much closer look at these two Types of Intermolecular Forces.