1. Physical Chemistry A Very Brief Introduction Aleksey Kocherzhenko March 14, 2013

2. What Is Physical Chemistry?
Physical Science
is that department of knowledge which relates to the order of nature, or in other words, to the regular succession of events.
All chemistry is a branch of physical science

3. What Is Physical Chemistry?
The name of physical science, however, is often applied in a more or less restricted manner to those branches of science in which the phenomena considered are of the simplest and most abstract kind, excluding the consideration of the more complex phenomena.
James Clerk Maxwell, “Matter and Motion”, 1876

4. What Is Physical Chemistry?
Chemistry started out as an empirical science
Synthetic chemists: think in terms of functional groups
Biochemists: concerned with the functionality of large molecules
Physical chemists: – often look at phenomena at an atomic and even subatomic level – describe phenomena in an abstract mathematical way

5. What Is Physical Chemistry?
Traditionally included are:
Thermodynamics
Kinetics
Quantum mechanics
as applied to molecular-level phenomena

6. A Great Textbook D. A. McQuarrie and J. D. Simon
Physical Chemistry: A Molecular Approach University Science Books, 1997

7. Quantum Mechanics and Chemistry
ortho
meta
para
Reactivity is determined by orbital symmetry…
… in many cases, so are functional properties!

8. Orbits vs. Orbitals Planetary atomic model Plum pudding atomic model
Ernest Rutherford
J.J. Thomson
Planetary atomic model
Plum pudding atomic model

9. Orbits vs. Orbitals
The absorption/emission spectra of atoms are discrete, not continuous!
Rydberg’s formula:

10. Principal quantum number n = 1, 2, 3, …
Orbits vs. Orbitals
Niels Bohr
Coulomb force
Centripetal force:
Angular momentum quantization:
Principal quantum number n = 1, 2, 3, …
Reduced Planck’s constant
Model of an H-like atom
where
Bohr radius

11. Orbits vs. Orbitals Energy levels of a hydrogen-like atom:
Rydberg constant, R
Planck constant:
Correct absorption frequency:
to satisfy Rydberg’s formula:
n = 1
n = 2
n = 3
n = ∞
E = 0
n = 4
E = –13.6
E = –3.40
E = –1.51
–0.85
E (eV) +

12. Orbits vs. Orbitals Photoelectric effect: light consists of particles?
Interference: light is a wave
Louis de Broglie
Light (and everything else) has both particle-like and wave-like properties
De Broglie wavelength:
Or:
(angular wavenumber)
(angular frequency)

13. Particle-wave duality

14. Orbits vs. Orbitals Particle in centrosymmetric potential:
“Old” quantum theory
n = 1
n = 2
n = 3
n = ∞
E = 0
n = 4
E = –13.6
E = –3.40
E = –1.51
–0.85
E (eV) +
Wave in centrosymmetric potential:
“New” quantum theory

15. Orbits vs. Orbitals
n = 1
n = 2
n = 3
n = ∞
E = 0
n = 4
E = –13.6
E = –3.40
E = –1.51
–0.85
E (eV) +
Electrons in atoms are found in stable (time-independent) states
Electrons behave as waves
Stable electronic states (orbitals) are standing waves

16. What a Typical PChem/QMech Course Covers:
0) Mathematical background and notation
Foundations of quantum mechanics
Postulates, equation of motion, stationary states
2) Simple model systems
Particle-in-a-box, harmonic oscillator, hydrogen atom, barriers
3) Multi-electron atoms
Approximate methods, spin
4) Molecules
Orbital hybridization, chemical bonding
5) Spectroscopy
Degrees of freedom, types of spectroscopy to probe them
6) The paradoxes of quantum mechanics and its relationship to classical mechanics