1. A beginners guide to atomic physics
Inside the atom
A beginners guide to atomic physics

2. Brief History JJ Thomson Rutherford Discovered the electron
Where is it?
Plum pudding Model
Rutherford
Gold foil experiment
Positive nuclear core

3. Problems with classical model
Coulomb force could make electrons orbit nucleus like planets, BUT…
Accelerated charge is supposed to emit EM waves…why is atom stable?
Also, why do atoms emit and absorb only discrete frequencies of radiation?

4. BOHR ATOM En= (-13.6 eV) 1/n2 (where n is an integer)
Circular electron orbits
Only “stationary” orbits allowed
The energy of each orbit is given by:
En= (-13.6 eV) 1/n2 (where n is an integer)
Photons of the correct energy are absorbed, “exciting” the atom into a higher energy orbit
Photons are emitted when the electron makes a transition to a lower energy orbit
The energy of the photons corresponds to energy difference of the two orbits DE=hf

5. Bohr atom (continued) Bohr atom...java applet
What wavelength of radiation would excite the hydrogen atom from the ground state (E1) to the third energy level?
E1 = eV/1 = eV E2 = -13.6/9 = -1.5 Ev
hc/l = 12.1 eV l = 1243 eV-nm / 12.1 eV = 100 nm

6. What possible wavelengths of light could be emitted when a hydrogen atom “de-excites” from the 4th energy level?
-0.82 eV
-1.51 eV
-3.4 eV
-13.6 eV

7. Stationary orbits Conservation of energy: KE + PE = Etot
½ mv2 – ke2/r = Etotal
Circular motion:
F=ma  ke2/r2 = mv2/r  ke2/r = mv2
Combined:
Etotal= mv2 – ½ mv2 = -½ mv2 OR
Etotal = ½ ke2/r – ke2/r = -½ ke2/r

8. Stationary orbits (continued)
Which orbits are allowed?
One way of getting the answer is to look at deBroglie wavelength of electrons.
l=h/mv
To “fit” in a particular orbit, 2pr=nl