Molecules attract each other, and the force of attraction increases as intermolecular distance decreases. In liquids, molecules are very close to each other and are constantly moving and colliding. In a gas, molecules are much further apart than in a liquid. Boiling points and melting points are largely determined by intermolecular interactions in the liquid. As molecular weight increases, intermolecular forces get much stronger as well. Intermolecular forces are also much weaker than intramolecular bonds. London dispersion forces are the weakest intermolecular force. They exist in every molecule. The larger the molecule the larger the polarizeablility of the molecule. Dipole induced dipole are the next weakest. It occurs in a molecule when it has a very small dipole moment. Next is dipole dipole. The strength of a dipole dipole interaction on the dipole moment and how closely the molecules approach one another. In a solid, molecules are held close together in a regular pattern by dipole dipole forces to minimize repulsions and maximize attractions. Dipole-dipole forces only occur if the molecule is polar. The strongest of the intermolecular forces is hydrogen bonding. Hydrogen bonding can only occur with Nitrogen, Oxygen, and Fluorine. These intermolecular forces are all called van der waals forces.
In the water POGIL we learned that covalent bonds occur in a single molecule of water. These bonds are intramolecular. We used the femto beaker of water and the molecules with magnets to represent water. Unlike other molecules, when water freezes the volume increases. When pressure is applied to ice, the volume decreases and it becomes liquid. When you apply pressure to ice, the structure breaks and you melt ice due to pressure, so you're able to skate on ice.
We also learned about a fifth type of force - ion dipole interactions. The strength of these forces are what make it possible for ionic substances to dissolve in polar solvents. If cation-anion attractions are stronger than ion dipole attraction, the compound will not be soluble.
I'd give my understanding this week about an 8. I definitely understand the different types of intermolecular forces and how melting and boiling point goes up as molecular weight goes up. I also understand that the higher molecular weight means more polarizability, which means a higher boiling point. I understand that every molecule has London dispersion forces. I'm still a little unclear on how to determine which gas is more soluble, but I think if I go over the Powerpoints and lectures I'll be able to understand it.
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