Many of the chemical processes that occur are driven by the innate attractions that different molecules and compounds have between each other. These attractions between molecules are guided by their properties, and can be explained through hydrogen bonds
There are a couple major types of intermolecular forces, and we must explore these forces in order to understand the interactions that occur between molecules. The forces will be detailed in order of increasing strength.
LONDON DISPERSION FORCES
These forces are the weakest types of inter-molecular forces. London Dispersion forces are caused by momentary dipoles that form in molecules. These dipoles form due to a momentary dis-symmetry in the molecule, or fluctuation in the molecules' electron cloud.
This basically means that in one moment, due to a disruption in the electron cloud, there are more electrons on one side of the molecule than the other. This forms a temporary dipole in the molecule. If two atoms or molecules are in close proximity, one of these dipoles may induce another, and thus these two molecules will reorient themselves and interact with one another.
The ability and extent to which a molecule can experience London dispersion forces is determined by the size of its electron cloud. Larger electron clouds indicate a greater chance for interference and thus momentary dipoles, and the extent to which this can occur is called the polarizability of a molecule.
Molecules with greater greater numbers of electrons have larger electron clouds, and thus are more polarizable; molecules with larger electron clouds have greater London Dispersion Forces.
DIPOLE-DIPOLE FORCES
Dipole-Dipole forces are forces that occur between opposite charged ends of two polar molecules. The positive end of a molecule attracts the negative end of another molecule, and these two ends interact with each other.
Dipole-Dipole forces are stronger than London Dispersion forces. Molecules polarity is caused by the uneven distribution of electrons throughout their molecule. An imbalance in electron distribution due to electronegativity differences in molecule cause these strong inter-molecular forces.
The strength of dipole-dipole forces can be gauged by the relative differences in charge across a molecule. More polar molecules will experience greater dipole-dipole forces. The strength of the overall dipole determines the intensity of the dipole-dipole forces.
HYDROGEN BONDING
Hydrogen bonds are a special type of dipole-dipole force. This type of force requires an extremely strong bond between the Hydrogen atom of one molecule and the highly electronegative Nitrogen, Oxygen, or Fluorine atoms.
(comment below if you know why they are so electronegative) (hint: look at the last blog).
The great strength of hydrogen bonds can be explained by the criteria for classification as a hydrogen bond. Since the hydrogen atom of one molecule is bonded to a very electronegative N, O, or F atom, the electronegative atom pulls the bonded electrons toward itself very strongly, causing a high charge density and a very strong dipole.
Then, this hydrogen atom can form very strong dipole dipole forces with other N, O, F atoms and interact with it in a very strong manner. Thus, hydrogen bonding is the strongest intermolecular force.
OTHER INTERMOLECULAR FORCES
Ion-dipole forces: These are intermolecular forces that form commonly when a ionic compound is dissolved in a polar solvent. The ions interact with the dipoles and the polar molecules orient themselves to the ion.
Dipole induced dipole forces: Just as in London Dispersion forces, how one temporary dipole can induce another, when a nonpolar molecule comes close to a polar molecule with a dipole, it interacts with it. However, these forces are relatively weak, which can explain why nonpolar solutes have great difficulty dissolving in polar solvents.
Isn't this some pretty FON stuff? Anyways, thanks for reading! Look at the other blogs, and comment below if you have any questions. Have fun studying!
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