Final answer:
Intermolecular forces are the attractive forces between molecules, including dipole-dipole interactions, hydrogen bonding, and the weakest, London dispersion forces. These are proposed by Fritz London and arise from temporary dipoles caused by electron movement, affecting the physical properties of substances.
Step-by-step explanation:
Intermolecular forces (IMFs) are the attractive forces that occur between molecules. Among the three types of van der Waals forces, which include dipole-dipole interactions, hydrogen bonding, and London dispersion forces, the London dispersion forces are considered the weakest.
Dispersion forces, proposed by Fritz London in 1930, arise due to the constant motion of electrons within atoms and nonpolar molecules, leading to temporary, instantaneous dipoles. These temporary dipoles induce dipoles in neighboring atoms or molecules, resulting in a weak electrostatic attraction. London dispersion forces are present regardless of the nature of the atoms or molecules composing the substance, making them a universal type of IMF.
These forces are significant because they can influence the physical properties of substances, such as their boiling and melting points. The strength of London dispersion forces increases with the size of the molecules or the number of electrons present, which can explain why larger molecules have higher boiling and melting points compared to smaller ones at the same temperature.