1. Chemistry 141 Friday, December 1, 2017 Lecture 35
Chemistry 11 - Lecture 11
9/30/2009
Chemistry 141
Friday, December 1, 2017
Lecture 35
Kinetic Molecular Theory of Gases

2. Energy levels for 2p MOs σ*2p π*2p 2p 2p π2p σ2p σ*2s 2s 2s σ2s XA X2XB

3. s-p Orbital Interactions

4. Energy levels for 2p MOs σ*2p σ*2p π*2p π*2p 2p 2p 2p π2p σ2p σ2p π2pXA X2 XB XA X2 XB

5. MO Diagrams for 2nd Period Diatomics

6. Heteronuclear diatomics: NO
σ*2p
Example: NO (5 + 6 = 11 valence e–)
Electron configuration:
(σ2s)2(σ*2s)2(σ2p)2(π2p)4(π*2p)1
Where is the unpaired electron?
MO scheme suggests more density on N
This is in agreement with the Lewis structure:
π*2p 2p
π2p 2p
σ2p
σ*2s 2s 2s
σ2s N NO O
N O : .

7. Molecular Orbital Theory
Two models of bonding
Hybridization
Simple
Hybridization of valence shell s,p, and d orbitals on one atom to form new atomic orbitals with the correct geometry
Atomic orbitals on adjacent pairs of atoms overlap to form bonds
Electrons are shared by only 2 atoms
Molecular Orbital Theory
Simple only for diatomic molecules
Atomic orbitals on all atoms combine to form molecular orbitals
Electrons fill molecular orbitals; bonds form when there are more e- in bonding than antibonding orbitals
Electrons delocalized over molecule
Doesn’t handle resonance
excited states O2 paramagnetism
Does handle resonance
excited states O2 paramagnetism

8. Recall that for gases Pressure is proportional to temperature
Pressure is inversely proportional to volume
Can we explain these observations in terms of motions of individual gas molecules?

9. Principles of Kinetic Molecular Theory
A gas is many small particles in constant, linear motion.
The majority of the volume of a gaseous substance is empty space.
Particles collide with each other and with the walls of the container.
Intermolecular forces are negligible, other than collisions.
Total kinetic energy remains constant, though individual particles may gain or lose energy via collisions.

10. Distribution of speeds

11. Speed vs. molecular mass

12. Effusion & Diffusion
Effusion is the escape of gas molecules through a tiny hole into an evacuated space.
Diffusion is the spread of one substance throughout a space or a second substance.

13. Principles of Kinetic Molecular Theory
A gas is many small particles in constant, linear motion.
The majority of the volume of a gaseous substance is empty space.
Particles collide with each other and with the walls of the container.
Intermolecular forces are negligible, other than collisions.
Total kinetic energy remains constant, though individual particles may gain or lose energy via collisions.

14. Real Gases