Intermolecular Forces (Day 3)

2/6/14
Scribe Post: Juliette Ovadia

Agenda

First, Mrs. Friedmann checked in our homework. The homework was two worksheets, the Intermolecular Forces table and the eight questions on the Intermolecular forces worksheet. Next, we had a discussion about Solar Roadways which was brought up yesterday and other such innovations. We then went over the homework and Mrs. Friedmann answered our questions about the worksheets, web assigns, and review packet. We were supposed to also complete a lab, the Physical Properties of Liquids Lab, but we did not have time to complete it. 

Class Discussion

At the beginning of class, we watched a video about Solar Roadways. According to the website, "The Solar Roadway is a series of structurally-engineered solar panels that are driven upon. The idea is to replace all current petroleum-based asphalt roads, parking lots, and driveways with Solar Road Panels that collect energy to be used by our homes and businesses." 

More information can be found on this website: http://www.solarroadways.com/intro.shtml, and the video above is a short documentary about the innovation.

We also discussed the idea that it is the small solutions that make the greatest impact. For instance, in third-world and developing countries especially in Africa,  people have to trek for miles carrying heavy tanks to get water, and usually those making that trek are women. The Hippo Water Roller was invented as an easier, less taxing way of carrying water. The video above details the innovation.  

We also discussed solar power, and how we can innovate so that we are not so reliant on fossil fuels. Illinois uses a lot of nuclear energy, yet even nuclear energy comes with its own problems. There is a very interesting growing field called biophotovoltaics, which is working on artificial photosynthesis and how we can harness the power of the sun and plants for solar power. Specifically, a recent paper by Andreas Mershin and some researchers at MIT details how Photosystem I can be aggregated from discarded crops or timber, stabilized by some chemicals, and spread out on a "nanoforest" of semi-conducting electrodes of ZnO nanowires and TiO2 nanostructure that can produce an electric current when exposed to light. This could mean that in a few years people in third-world and developing countries could use discarded plants, a bag of chemicals and some written instructions and paint this/install this on their roof and have solar power. Right now the efficiency is only at 0.1-0.8% but the field is clearly advancing and such an innovation would be extremely useful and life-changing in developing countries. Click here for the link to the paper on this biophotovoltaics innovation 

Homework

We went over both of the worksheets in class today. Important things to remember about intermolecular forces:

• Nonpolar--> main IMF London Dispersion Forces even though LDF is at work in every molecule (symmetrical)

• Polar --> main IMF Dipole-Dipole (assymetrical)

• Usually, if polar w/out a hydrogen attracted to O, N, F (FON) --> dipole/dipole 

• If Nonpolar --> London Dispersion Forces

• Polar w/ H attracted to F, O, or N--> Hydrogen Bond

• In addition, these intermolecular forces are on a continuum. We learn the extremes, and the muddy area is for experimentation.  H Bond (strongest) <----------> London Dispersion Forces (weakest)

Key to Worksheet 8 Questions

We also discussed CH4O, methanol. The lewis structure is to the left. Remember, any molecule with an O-H bond is an alcohol (though not necessarily alcohol as in beer and wine). In CH4O, the main IMF is Hydrogen Bonding, which is stronger and better at sticking molecules together and therefore is the stronger/main IMF. Mrs. Friedmann also showed us the lewis structure for ethanol, which is what is in the beverage alcohol. The lewis structure for ethanol is above.  Ethanol also has an O-H bond so has H-bonding. Methanol is wood alcohol, a paint thinner that is dangerous to drink. During the Great Depression and Prohibition, alcoholics drank methanol as an alternative to beer and wine. The body metabolizes ethanol into ethaldihyde, however that same enzyme does the same chemical reaction to methanol and turns it into formaldihyde. Formaldihyde is dangerous because it freezes molecules into place and preserves them, essentially "pickling" the body. The "cure" is to drink a lot of alcohol. 

In addition, we discussed hydrocarbons. With an extremely long chain of hydrocarbons, even if there is an oxygen connected to a hydrogen, the main IMF would be London Dispersion Forces because of the great amount of hydrocarbons. The longer the non-polar side, the stronger the LDF and the increased viscosity.

Key to Worksheet w/ Table

On the second worksheet with the table, the answer to the motor oil question is as follows on the key:

Since motor oil is needed to quickly coat all surfaces of an engine to keep them from getting too hot, a low viscosity material is better than a high viscosity material. 

*Viscosity= measure of how well substances flow

*contains H-bond which means high velocity, motor oil has LDF only so it has low viscosity

We also went over sigma and pi bonds, that a pi bond is the last pair of electrons for example on the S in SO2 which spreads out and balances the structure. A pi bond is ultimately an area of space electrons can occupy, orbitals available. The key is that electrons don't stay stuck in between 2 atoms in a pi bond, if there is an empty pi bond they will smear onto it and occupy the entire space, and we show resonance to demonstrate this.

Had we done the lab, we would have worked with:

1) Hexane --> no polarity so main IMF is LDF and would evaporate quickly and have a low boiling point

Hexane

2) Vegetable Oil --> LDF and Dipole-dipole and polarity, but the predominant intermolecular force is LDF

3) Water --> Hydrogen bonding

Homework

Study for Unit 8 test tomorrow! 
A good way to study would be to work on the review packet. The key is posted on moodle. 

The next scribe post author is: Valerie Korol