Intermolecular forces occur between molecules. Although intermolecular forces are weaker than chemical bonds, they are very significant in determining the physical and chemical properties of substances. There are three principal types of intermolecular force: 1) dipole-dipole forces, which occur between polar molecules 2) London dispersion forces, which occcur due to small instantaneous dipoles and 3) hydrogen bonding, which occur between molecules in which hydrogen is bonded to a small electronegative atom such as oxygen. Because the polarity of such molecules is occupied on one end by a bare hydrogen proton, without inner shells of electrons to shield it, hydrogen bonding gives rise to intermolecular forces which are significantly stronger than any other type.
Because intermolecular forces are of great importance in living organisms, this topic is of major MCAT importance. The MCAT will often pose both explicit questions from this topic and questions depending on reasoning which takes intermolecular force as its starting point. Furthermore, many other topics, such as States of Matter or Solutions in Chemistry or Proteins or Membranes in Biology greatly rely on your understanding of Intermolecular Forces.
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Conceptual Vocabulary for Intermolecular Forces