Intermolecular Forces (IMFs) POGIL

In order to better understand the term "intermolecular force", let's look at each part of the phrase. "Inter" = between, "molecular" = molecules, and "force" = attraction or repulsion. So, "intermolecular force" just means attraction/repulsion between molecules.

Intermolecular forces are different from intramolecular forces, which are called "bonds". In the following picture, the solid line represents the bond between the H and Cl, while the dotted line represents the IMF between two HCl molecules. (NOTE: The "δ" symbol represents a dipole.)

Dispersion forces (also called London dispersion forces and Van der Waals forces) occur in all substances but are the only IMF for non-polar molecules.

To understand how dispersion forces form, let's look at the following analogy.

The momentary (also called instantaneous) dipoles that form when electrons become unevenly distributed in an atom or molecule cause dispersion forces.

As the number of electrons increases, there is an increased chance of momentary dipoles forming. The more momentary dipoles there are, the stronger the dispersion force.

Dipole-dipole forces occur between substances with permanent dipoles. A dipole is a partial charge created by the electronegativity difference between atoms in a bond. "δ+" means a positive dipole, while "δ-" means a negative dipole.

For example, carbon monoxide has a positive dipole in the carbon atom and a negative dipole on the oxygen atom.

When CO molecules are around each other, the dipoles attract and repel each other based on their electrostatic attraction. These attractions are the dipole-dipole force.

Hydrogen bonds are IMFs that form between molecules with very strong dipoles. The strongest dipoles occur when hydrogen is bonded to nitrogen, oxygen, or fluorine.

Use the following information to help identify the IMFs in each molecule.