Density is the amount of mass per unit of volume. Density is calculated using the equation: Density = mass/volume. Anything which increases the amount of mass in a particular volume will increase the density. Anything that decreases the amount of mass in a particular volume will decrease the density.
Intermolecular forces are the forces of attraction that hold bonded atoms together. Some intermolecular forces are fairly weak, while others are relatively strong. Below is a list of different types of intermolecular forces. The list is arranged from weakest to strongest.
Dispersion Forces Weak
Ion-Dipole Forces Strong
We can think of matter as being composed of small particles. Each particle is composed of one or more atoms. When the particles of a substance are held together by strong intermolecular forces, they are held closer together. This means that for a given volume, more particles would be present in the sample. The presence of more particles results in a higher mass per unit of volume and therefore a higher density. When the particles of a substance are held together by weak intermolecular forces, they are not held as closely together. So, for a given volume, fewer particles would be present in the sample. The presence of fewer particles results in a lower mass per unit of volume and therefore a lower density.
Temperature is an indication of the average kinetic energy of the molecules of a substance. As temperature increases, the kinetic energy of the particles increases and the density decreases as the molecules move farther away from each other. Similarly, a decrease in temperature results in slower moving molecules that stay closer together. A decrease in temperature will cause the density to increase.