Dispersion Forces!. By: Lisa, Alyssa, Brandon and Liam. They are the weakest kind of intermolecular attraction and occur between molecules.
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By: Lisa, Alyssa, Brandon and Liam
They are thought to be caused by the motion of electrons. This is because they are a temporary attractive force that results when the electrons in two adjacent atoms occupy a position that make the atoms form temporary dipoles.What are Dispersion Forces?
The strength of dispersion forces increases as the number of electrons in a molecule increases.
The more electrons in a molecule, the greater its dispersion forces. A good example of this is the halogen group.
Fluorine and chlorine do not have very many electrons and consequently have relatively weak forces of attraction between their molecules.
The attractions being weak allows the molecules to move around more and that is why fluorine and chlorine are
gasses at STP.Electrons Influencing Dispersion Forces
This causes the forces of attraction to be greater between the molecules in bromine. They can not move around as much as the molecules in fluorine and chlorine, so bromine is a liquid at STP.Electrons Influencing Dispersion Forces
The dispersion forces being even greater than with bromine, the molecules can’t move around at all, they can only vibrate.
Bromine and astatine are solids at STP.Electrons Influencing Dispersion Forces
They were named the London forces in honor of the German physicist; Fritz London who studied these forces!!
Also Known As...
Fritz London (1900-1954)
Unlike the name London forces, van der Waals forces refers to the collective grouping of the weakest attractions between molecules.
This includes dispersion forces as well as dipole interactions.
Johannes van Der Waals (1837-1923)
We have already learned about dipole interactions. We know that they are a weak intermolecular force and result from the attraction of oppositely charged regions of polar molecules. Now we will learn how dipoles and ions can induce these intermolecular forces.
charged balloon attract the negative charges in your hair.
When an ion comes in close contact with a non-polar molecule the non-polar molecule becomes momentarily polarized, and the two molecules are attracted to each other.Ion-Induced Intermolecular Forces
These bond vibrations actually cause momentary, uneven distributions of charge. So they can actually cause non-polar molecules to become slightly polar for an instant.Temporary-Induced Polar Molecules
This as well as ion-induced dipole forces, results in intermolecular forces of attraction, also known as dispersion forces, between molecules!
So, in other words the likely-hood that the even distribution of charge will be disrupted within a molecule (by the temporary induction of a dipole or ion) is referred to as the molecule’s polarizability.Polarizability