KEY2CHEM

Interparticle Forces

Interparticle forces are electrostatic attractions that exist between molecules, ions, or atoms in a collection of particles. Unlike chemical bonds, which hold individual atoms together with strong forces, interparticle forces are weaker electrostatic attractions that hold collections of particles together. They can be categorized as ion-dipole, hydrogen bonding, dipole-dipole, dipole-induced dipole, and dispersion forces depending on the types of particles that interact.

Example 1.

Which molecule is expected to have the strongest type of interparticle forces?

A. $$\require{mhchem}\ce{H2O}$$

B. $$\require{mhchem}\ce{CH4}$$

C. $$\require{mhchem}\ce{F2}$$

Solution

A. $$\require{mhchem}\ce{H2O}$$

All of these substances have dispersion forces, but water also has hydrogen-bonding, which is a stronger type of dipole-dipole interaction.

Example 2.

Which substance will have the strongest dispersion forces?

A. $$\require{mhchem}\ce{CH4}$$

B. $$\require{mhchem}\ce{C5H12}$$

C. $$\require{mhchem}\ce{C8H18}$$

Solution

C. $$\require{mhchem}\ce{C8H18}$$

Due to the larger number of electrons and greatest surface area, $$\require{mhchem}\ce{C8H18}$$ is expected to have the strongest dispersion forces.

Example 3.

Which is an example of an interparticle force?

A. the H-O bond in water ($$\require{mhchem}\ce{H2O}$$)

B. the hydrogen bonds between water molecules in $$\require{mhchem}\ce{H2O}$$

C. the C-H bond in methane ($$\require{mhchem}\ce{CH4}$$)

Solution

B. the hydrogen bonds between water molecules in $$\require{mhchem}\ce{H2O}$$

Interparticle forces exist between particles/molecules. Chemical bonds exist between individual atoms in a molecule.