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Why is that the bigger the molecule, the stronger the Van der waal's forces

bewteen molecules?

Also, how is a dipole induced?
Bigger molecule -> more electrons -> more vdw forces.
Larger molecules have greater van der walls forces as there are MORE electrons which means MORE charge which creates MORE electrostatic attraction between molecules
As for a dipole, a dipole is the result of an uneven distribution of charge across a molecule (i.e. all the positive charge is on one side and all the negative charge is on the other)

A good example of a polar molecule (a molecule with a dipole) is water
Water has 2 Hydrogens which are both on the same side of the Oxygen due to the molecule being 'bent' shaped. Due to oxygen being much more electronegative than hydrogen, the electrons in the covalent bond are attracted more toward the oxygen than the hydrogens.

this means that the oxygen end of the molecule becomes slightly negatively charged and the hydrogen end becomes slightly positivley charged

This creates an uneven distribution of charge across the molecule as the hydrogen end is positively charged whereas the oxygen end is negatively charged, meaning that the water molecule has a dipole pointing in the direction of the Hydrogens

If you don't understand something i've just said then sorry, just ask and i'll try to explain it as best I can :biggrin:
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ozmo19
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Original post by SANTR
bewteen molecules?

Also, how is a dipole induced?


Original post by ATLHustler
Bigger molecule -> more electrons -> more vdw forces.

This..

As for induced dipoles, this link will give you good information;
http://www.chemguide.co.uk/atoms/bonding/vdw.html
In some syllabuses (syllabi?), the term "van der Waals" can refer to all intermolecular forces (even dipole-dipole ones) so London/Dispersion forces are preferred.

If you've already been taught that electrons shouldn't be thought of as point-particles, but more "spread out" as a probability wave, then at any particular point some parts of the atom will have more electron density than others by chance. These areas are partially charged (represented by a delta-negative symbol) with temporary dipoles.

The more electrons in an atom or molecule, the higher the electron density at those regions, so the delta-negative areas will have a greater charge. Therefore with a greater charge, the electrostatic attractions between larger molecules (with more electrons) will be stronger.

In a very simple way, you can think of it as a bigger (temporary) charge because there's more electrons. To answer your query about induced dipoles, that's about the electron cloud distortions caused by an atom or molecule with dipoles.

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