2019-2020 Updated IMF Material

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The following information needs to be modified due to more specific explanation of Intermolecular Forces (IMF).

van der Waals forces is the name people give to both dipole-dipole IMF (D - D), between two polar molecules, and London dispersion forces (LDF), between 2 non-polar molecules.

Therefore, Hydrogen bonding (H - B) is not considered a van der Waal force because Hydrogen bonding IMF is larger (or stronger) IMF than van der Waals forces. Remember, H - B is the special very large dipole - dipole IMF caused when by dipoles that contain H - F bond, H - O bond and/or H - N bond since these bonds have high Δ EN (electronegativity difference) but more importantly the non-hydrogen atom are small radii atoms (causing higher Coulombic force).

With respect to London dispersion forces (LDF), actually all compounds and even single atoms have LDF. Remember, LDF is caused by the fact that the electrons in atoms and/or molecules are in constant motion so there is always times where electrons are not equally distributed over the element and/or compound causing an Instantaneous dipole (unevenly distribution causes a partial negative and partial positive area of the species making instantaneous Coulombic forces). This instantaneous Coulombic forces only exist of a short period of time (billionth of a second) so it is a very weak force.

<b>Therefore, all species have LDF (or some times dispersion forces) but most of the time, the other IMF make the LDF force insignificant.


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Edited April 10, 2020 8:06 am (diff)
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