1. Electron Configuration and Chemical Periodicity
Chapter 8
Electron Configuration and Chemical Periodicity B 5
10.811 C 6
12.011 N 7
14.007 O 8
16.000 F 9
18.998 Ne 10
20.18

2. Stern-Gerlach Experiment
Vacuum
North
South
Ag atoms
Furnace 1000C
Ag vapor
Ag atoms

3. Stern-Gerlach Experiment
No Ag spots observed!
Walther Gerlach
Otto Stern
...as the story goes
...Stern smoked bad cigars
...Breathed on the collector plate (breath contained sulfur!)
Collector Plate
...Trace Ag converted to Ag2S
...Making the spots visible!
...Conclusion: Two types of electrons!

4. Stern-Gerach Experiment
Electrons come in two different types are identified by the electron spin quantum number ms
ms = +½ (“Spin up”)
ms = - ½ (“Spin down”)

5. Pauli Exclusion Principle
No two electrons can have the same set of four quantum numbers (n l ml ms) in the same atom.
2px
n = l = ml = -1
ms = +½
n = l = ml = -1
ms = +½
ms = -½
Maximum Capacity for 2px is 2 electrons!

6. Electron Count 2s 2px 2pz 2py n = 2 l = 0 ml = 0 ms = +½
n= 2: electrons from 2s electrons from 2p = 8 electrons total
Total electrons = 2  n2
= 2  22 = 8 electrons total!