A. London dispersion forces, B. dipole-dipole interaction, QUESTION: Which type of intermolecular forces is present between any pair of molecules? A. London dispersion forces, B. dipole-dipole interaction, C. hydrogen bonding interaction Dipole-dipole interaction occurs only between two molecules that are polar. London dispersion forces occurs between any pair of molecules. Motion of electrons leads to temporary polarizations in any molecule. Hydrogen bonding interaction occurs when one molecule has a hydrogen atom bonded to a highly electronegative atom (F, O, N), and the other molecule has a highly electronegative atom with a lone pair. QUESTION: Which type of intermolecular forces is present between any pair of molecules? A. London dispersion forces, B. dipole-dipole interaction, C. hydrogen bonding interaction PAUSE CLICK Dipole-dipole interaction occurs only between two molecules that are polar. So, choice B is incorrect. London dispersion forces occurs between any pair of molecules. Motion of electrons leads to temporary polarizations in any molecule. Choice A is the correct answer. Hydrogen bonding interaction occurs only when one molecule has a hydrogen atom bonded to a highly electronegative atom (F, O, N), and the other molecule has a highly electronegative atom with a lone pair. Choice C is incorrect. CLICK CONTINUED ON NEXT SLIDE

Example of dipole-dipole interaction between two HCl molecules Example of dipole-dipole interaction between two HCl molecules. Partially-positive end of one molecule is attracted to the partially-negative end of the other molecule. Here is an example of two molecules that can interact by dipole dipole interaction. An HCl molecule is polar. Since chlorine is more electronegative than hydrogen, the chlorine end of the molecule has a partial negative charge. HIGHLIGHT delta (-) and the hydrogen end has a parital positive charge. HIGHLIGHT delta + Attraction occurs between the two molecules because of these partial charges. THe partial negative end of one molecule is attracted to the partially positive end of the other molecule. CLICK CLICK CONTINUED ON NEXT SLIDE

Example of hydrogen bonding interaction Example of hydrogen bonding interaction. Hydrogen bonded to a highly electronegative atom is strongly attracted to lone pair of a highly electronegative atom in the a neighboring molecule. Here’s an example of hydrogen bonding interaction between two molecules. Hydrogen bonding occurs when one molecule has a hydrogen atom that is bonded to a highly electronegative atom In the example shown here, this hydrogen atom. CLICK is bonded to a oxygen. Because oxygen is highly electronegative, the hydrogen atom is almost stripped bare of electrons. It will be strongly attracted to a lone pair on neighboring molecule. This strong interaction, indicated here by a dashed line, is weaker than a covalent bond, but is stronger than dipole-dipole interaction. Between small molecules, like water molecules, it is also stronger than London dispersion forces. For very large molecules, the predominant attractive force among molecules is London dispersion. CLICK PAUSE END RECORDING

Video ID: 3-13-1 © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08