Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 109 - General Chemistry - Spring 2015

Lecture Notes 34: 22 April

PREVIOUS

Molecular Orbital Model of Bonding, cont.

Molecular Orbital Energy Levels and Bonding in Diatomic Homonuclear Molecules, Li2-Ne2
  Li2 Be2 B2 C2 N2 O2 F2 Ne2
sigma2p*               sigma orbital diagram with paired arrows
pi2p*           pi orbital diagram with 2 unpaired arrows pi orbital diagram with 2 sets of paired arrows pi orbital diagram with 2 sets of paired arrows
sigma2p         sigma orbital diagram with paired arrows pi orbital diagram with 2 sets of paired arrows pi orbital diagram with 2 sets of paired arrows pi orbital diagram with 2 sets of paired arrows
pi2p     pi orbital diagram with 2 unpaired arrows pi orbital diagram with 2 sets of paired arrows pi orbital diagram with 2 sets of paired arrows sigma orbital diagram with paired arrows sigma orbital diagram with paired arrows sigma orbital diagram with paired arrows
sigma2s*   sigma orbital diagram with paired arrows sigma orbital diagram with paired arrows sigma orbital diagram with paired arrows sigma orbital diagram with paired arrows sigma orbital diagram with paired arrows sigma orbital diagram with paired arrows sigma orbital diagram with paired arrows
sigma2s sigma orbital diagram with paired arrows sigma orbital diagram with paired arrows sigma orbital diagram with paired arrows sigma orbital diagram with paired arrows sigma orbital diagram with paired arrows sigma orbital diagram with paired arrows sigma orbital diagram with paired arrows sigma orbital diagram with paired arrows
Bonds  1 0 1 2 3 2 1 0
Paramagnetic N N Y N N Y N N

 

Homonuclear molecules, cont.

Last time we were looking at the various homonuclear molecules of Period 2. One of the problems of the model we used was that we would predict the sigma 2p orbital would be at a lowere enernergy than the pi 2p orbitals, but in the chartt above that is not the case. What is going on? The problem is that if we look at the orbitals one at a time (sigma separately from p) then the morsymmetrical sigma orbital will be lower in energy, but if we mix all three p orbitals in making our new molecular orbitals, then the energies shift to give us the combinations in the table. How do we knwo this is correct? Look at B2 and O2 where the Table predicts the molecules will be paramagnetic (they have unpaired electrons) where as the model with the sigma 2p at a lowere energy would give non-paramagnetic molecules.

Heteronuclear Molecules:

We've looked at homonuclear molecules where the initial orbital energies are identical, what about the more complex situation where two different atoms combine?

Molecular Orbital Energy Levels in NO
sigma2p*  
pi2p* pi orbital diagram with 1 unpaired arrow
sigma2p sigma orbital diagram with paired arrows
pi2p pi orbital diagram with 2 sets of paired arrows
sigma2s* sigma orbital diagram with paired arrows
sigma2s sigma orbital diagram with paired arrows
Bonds  2.5

H atom

HF molecule

F atom

up arrow

E
 

 empty sigma orbital diagram

sigma*

 

1ss orbital diagram with 1 unpaired arrows
 
 
 
 
 
 
 
 
 
 
p orbital diagram with 1 unpaired arrows2p
   

 sigma orbital diagram with paired arrows

sigma

 

Simple Models for Complex Molecules: Benzene texts

Models and theories:

Making molecular orbital theory work for larger molecules.

 

Solutions (Chapter 11)

Solution Concentrations-a Review & Some New Stuff.

Solutions —General Information

Solutions: a solution occurs when one chemical is completely dissolved or dispersed in another. We most commonly think of solutions as being liquid, but solid solutions also occur, such as the various metal alloys like steel, brass and bronze.

In a solution the substance present in highest concentration is considered to be the solvent, while components in lesser amounts are considered to be solutes. If you dissolve a sugar cube in water you get a sugar solution, where water is the solvent, and sugar is the solute.

FYI

Example:

  • What is the solvent in 80 proof rum: 80 proof = 40% alcohol in water, so water is the solvent.
  • What is the solvent in 151 proof rum: 151 proof = 75.5% alcohol in water, so alcohol is the solvent.

 Solubility

All gases are completely soluble in each other.

Liquid solutions

"Like dissolves like."

NEXT


Syllabus / Schedule
home "refractometer" icon
C109 Home
lecture "spectroscope" icon

C109 Lecture Notes

© R A Paselk

Last modified 20 April 2015