Week 5: Pumpkins and Mozart

Soundtrack for the week!

Here's a thought: Why isn't VSEPR pronounced vuh-seh-pur instead?

We kicked off the week by making more models. But instead of making electron-domain balloon models like this...

We made toothpick and gumdrop models like this. 

This was the second half of the VSEPR packet that we did. These models show the molecular geometry, which usually looks different from the electron domain geometry. They look so different because the balloon models show where each electron is likely (LIKELY) to be at any given moment. The gumdrop models show more the angles at which each atom is bonded to the central atom. The central atom isn't visible in the electron domain geometry, but it is visible in molecular geometry. The biggest difference is that molecular geometry models only physically show the electrons that exist in bonds, while electron domain geometry models also show nonbonded valence electrons. The point of this exercise was to make us have to actively think and work on how these models work with each other, rather than only having us do the lectures (which can get hypnotic and bland at times). As Dr. Finnan seems to think, others' failure is an excellent way to learn. Which is true.
In my understanding, the main idea of VSEPR is that the electrons and protons within each molecule naturally repel each other and attract each other. This makes them settle into certain shapes to be the least repellent and volatile. Kind of how the balloons settle to have the least friction.
Other things we did this week:

• Formal charges. Formula for calculating formal charge: FC = V - N - (B/2). You put the formal charge in the Lewis structure, then add them all up for the molecule. You always want the structure with the lowest charges, because it's more correct. 
• Hypervalency (and electron deficiency). Hypervalency is when a central atom holds more than eight valence electrons. This can only happen in periods 3-7 on the periodic table. 
  
  Phosphorus pentachloride, pictured above, is a prime example. Boron and beryllium may be electron deficient, given their number of orbitals. 
  
  
  Weekly chemistry joke: Helium walks into a bar and orders a drink. The bartender curses and yells "We don't serve noble gases here!"
  Helium doesn't react.
  Ba-dum-chhhh.