Experiments That Show Wave Property of Light

Physical Chemistry 20130501 week 5 Wendesday May 1, 2013 page 1 experiments that show wave property of light:

1. diffraction 2. Interference particle property of light:

1. photoelectric effect E=hν E is particle concept ν is wave property

Niels Bohr (1913) applied quantization to hydrogen atom

R is Rydberg constant = 1.096776*105cm-1 cm-1 is wavenumber(unit of energy) see spectrum handout

Spectral lines at first were empirical.

Bohr’s postulates:

1. Energy of the hydrogen atom is quantized. energy levels E1, E2, E3,… with E1

Each energy level is called a stationary state or allowed energy. Why doesn’t electron fall into nucleus?

2. An electron in a stationary state does not radiate electromagnetic energy (radiation).

3. Emission line spectrum results from the transition between upper stationary state and a lower stationary state.

4. The electron in a hydrogen atom stationary state moves in a circular path around the nucleus.

5. The angular momentum of the electron is quantized. (from deBroglie’s theory)

4 and 5 are false.

1. eq A is a difference formula

2. eq A is energy formula

Planck’s quantum of energy is incorporated A hydrogen atom has one electron, which orbits the nucleus at radius r. It’s attracted to the nucleus by the electric force. The electron is under acceleration, otherwise it would go in a straight line and not be bound to the atom.

Coulomb’s Law: in cgs units for convenience

Etot=KE+PE kinetic energy + potential energy

from I, (mvr)v=ze2, substitute into v

v=9.4*107cm/s for n=1, the first orbit

for n=1: E=-2.18*10-18J=-13.6eV for n=2: E=-5.4*10-19J=-3.40eV for n=3: E=-2.42*10-19J=-1.51eV

For n↑, E gets less negative. As n→∞, E→0, in which case it would be no longer bound to the nucleus (free electron).

1eV=1.60*10-19J=8066cm-1 eV is electron volts

Substitute for v in equation I: 2 rn=(.529Å)n

That formula is correct, even though it was derived based on two false assumptions.

Heisenberg threw in a monkey wrench…