Weekly blog 11/4 thorugh 11/10

This week, we learned about vapor pressures, lattice energies, boiling points, and how intermolecular forces affect each of these. The higher the boiling point of a substance, the lower the vapor pressure. This means that the more intermolecular forces in a substance there are, the lower the vapor pressure in that substance. Lattice energy increases as ion size decreases and charge increases. This is a result of the coulombic relationship in lattice energy. Lattice energy is actually correlated with melting point, because ions in a lattice are harder to break from that lattice as lattice energy goes up. This means that when there is more lattice energy, the melting point rises. Here is a link to some good review on lattice energy.

On friday we applied all of these concepts we have learned in an activity where we had to determine if specific substances were or were not conductive, and also we had to identify unknown elements based on their properties. The conductivity test was fairly simple; we put a probe in each of the substances and it told us whether or not it was conductive. We discussed why some substances were conductive only when in a liquid state, like salt. Salt breaks into ions which can then conduct electricity when in liquid form. As for the identifying unknown elements, it was fun. It was interesting to see how some molecules were more viscous than others and to be able to tell which molecule was which just based on things like solubility, viscosity, and vapor pressure. Even though they all had virtually the same viscosity except glycerin, we could still figure it out. The key was testing the solubility with water.

My understanding of what was going on in class is pretty good, I think that I could still understand better why some things are conductive as a liquid but not as a solid. It seems counterintuitive to me, why something that has less density could be more conductive than something with more density. However, I think I'll be able to figure it out. Hopefully Dr. J will have another chat room open on monday night, because I found that enormously helpful when studying for the test last time.

Weekly Blog 9/28 through 10/3

We began this week focusing on metallic bonding. We learned that in metallic bonding, there is essentially a cluster of cations with a "sea of electrons" flying around the cations, not associate with any particular atom. Also, alloys are made in two different ways: interstitial or substitial. Interstitial is when smaller atoms fill the space in between larger atoms, making the alloy more dense, and substitutional alloys are where two similarly sized atoms are mixed, which does not increase density. Here, substitutional is on the left and interstitial is on the right.

Alloys are essentially solutions of metals.

We also learned about the intermolecular forces, or IMF's, that exist such as hydrogen bonding, dipole dipole bonding, and LDF's, or London Dispersion Forces. These are all van der Waals forces. Ion-dipole bonding can also happen, but this is not a van der Waal force. Ion-dipole forces are the strongest, then hydrogen bonding, then dipole-dipole, then the LDF's (induced dipole-dipole and induced dipole-induced dipole). We learned that LDF's are present in all molecules, polar, non-polar, ionic, everything. They are, however, very weak and don't compare much to hydrogen bonding and ion-dipole bonding. Here is a good site about LDF's.

Another thing we learned was about the hydration spheres of ions in a solution, We saw that if you dissolve K+Cl- in water, the K and Cl will separate and get surrounded by water molecules. The water molecules will align themselves so that the positive end is towards the negative ion and the negative end is towards the positive ion. The sphere will also include hydrogen bonding because of the two hydrogens in water bonded to the oxygen.

I think I have a good understanding of the ideas we covered this week. I'm looking forward to seeing what role entropy plays in these molecules and also learning more about what entropy really is. I've heard of it before, but I get the impression that I don't know anything significant about it.