25
2024
-
03
Intermolecular interaction
Classification:
【Summary Description 】A molecule is a system consisting of a positively charged nucleus and negatively charged electrons, with molecules interacting with each other due to the interaction of charges. A molecule's charge distribution can be balanced so that the positive charge center and the negative charge center together, so that there is no permanent dipole and become non-polar molecules, such as carbon dioxide and methane; if the two centers do not coincide, an electric dipole is created and becomes a permanent dipole.
A molecule is a system composed of a positively charged nucleus and negatively charged electrons. Due to the interaction of charges, the interaction force between molecules and molecules occurs. The charge distribution of a molecule can be balanced so that the positive charge center and the negative charge center are combined together, so that there is no permanent dipole and becomes a non-polar molecule, such as carbon dioxide and methane; if the two centers do not coincide, an electric dipole is generated and becomes a permanent dipole or polar molecule, such as hydrogen chloride and methyl chloride. The interaction between two molecules with a permanent dipole is the first kind of interaction between molecules, also known as dipole-dipole interaction. The interaction between a polar molecule and a non-polar molecule is the second interaction, because the non-polar molecule can be induced to be polarized in the electric field of the polar molecule, so it is also called dipole-induced dipole interaction. Both of these interactions require that at least one of them be a polar molecule. The interaction between two non-polar molecules is the third interaction. This is because the movement of electrons in each molecule is induced by the influence of the other molecule. This force is first used by F.W. London. Calculated by quantum mechanics, it is called the London force, also known as the dispersion force or induced dipole-induced dipole interaction. The first force is stronger, the second force is the second, and the third force is the weakest, but the third force is universal. These interactions vary with the intermolecular distance r or 1/rn. The first interaction has a small value of n, so it works at a long distance; the second is second; the third is the largest, so it only works when the two molecules are very close. There is also a mutual repulsive force between molecules, which only works when they are closer together. There are also quadrupole interactions, which are generally weaker.
The interaction between molecules enables molecules to become condensed at low temperatures, which is also the source of a in the van der Waals equation, so it is also collectively referred to as the van der Waals force between molecules. Due to the interaction between molecules, the gas deviates from the ideal gas law when the pressure is high.
Another interaction between molecules is the transfer of energy when they collide with each other. Collisions can be elastic, not exchanging energy but only momentum, or inelastic, with energy exchange and energy conversion, such as the conversion of electronic vibrational energy into flat kinetic energy. The energy of the molecules reaches an equilibrium distribution over a longer period of exchange.