• Explain the statement “you need attractive forces to condense and repulsive forces
to freeze”.
o As mentioned above, the attractive forces actually cause the molecules in a gas to
collapse to a much denser solid or
...
• Explain the statement “you need attractive forces to condense and repulsive forces
to freeze”.
o As mentioned above, the attractive forces actually cause the molecules in a gas to
collapse to a much denser solid or liquid state. The difference between a solid
and a liquid, on the other hand, is that the molecules in a solid are fixed in space
whereas those in a liquid can move around. It is the short range repulsions that
hold the molecules in place in the solid state, because these are the interactions
that represents what happens when two particles come in contact. (To hold
something in place, even in common speech, means to put it in contact with
enough other objects such that it no longer has any place to move.)
• What are dispersion or London forces? Describe how they arise.
o Atoms and molecules are tiny highly charged positive centers surrounding by a
“cloud” of negative electrons. As the electrons move around the cloud changes
shape and “instantaneous” dipoles are created. These dipoles will then induce
dipoles in nearby atoms and molecules with the net effect of allowing for a
favorable dipole-dipole interaction. We call these forces between fluctuating
dipoles dispersion or London forces.
• Why are some substances gases at room temperature, but others are liquid or solid?
o It depends on their intermolecular forces; the stronger the intermolecular forces,
the more likely the substance is going to be a liquid or a solid at room
temperature. This is because it will take a stronger energy (heat energy, in our
case) to disturb the intermolecular forces in a liquid or solid than it will in a gas,
which we assume to
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