Dispersionijõud

Dispersionijõud, also known as London dispersion forces or simply dispersion forces, are weak intermolecular forces that arise from temporary fluctuations in electron distribution within molecules. These forces are present in all molecules and atoms, regardless of their polarity.

The origin of dispersion forces lies in the constant motion of electrons. At any given instant, the electron cloud around an atom or molecule may not be perfectly symmetrical. This temporary, random asymmetry creates a transient dipole moment. This instantaneous dipole can then induce a complementary dipole in a neighboring atom or molecule. The attraction between these temporary, induced dipoles constitutes the dispersion force.

The strength of dispersion forces depends on several factors, primarily the size and shape of the molecule. Larger molecules with more electrons have more diffuse electron clouds, leading to larger and more frequent temporary dipoles, and thus stronger dispersion forces. Similarly, molecules with elongated shapes tend to have stronger dispersion forces than more spherical molecules of similar molecular weight because their electron clouds can interact over a larger surface area.

Dispersion forces are significant in determining the physical properties of nonpolar substances, such as their boiling points and melting points. For example, the boiling points of noble gases increase down the group as the number of electrons and atomic size increase, leading to stronger dispersion forces. They also play a role in the interactions between polar molecules, though they are typically weaker than dipole-dipole interactions and hydrogen bonds.