1. Electron Configuration
A detailed way of showing the order in which electrons fill in around the nucleus

2. Electron Configuration Symbols
# of e- in sub level
Electron Configuration Symbols
1s 2
Energy Level
Sub Level
(s, p, d, f )

3. We must follow 3 rules… Aufbau priciple
Electrons occupy energy levels with lowest energy first.

4. Pauli exclusion principle
If 2 electrons occupy the same energy level they must have opposite spins.

5. Hund’s rule…
Electrons that occupy orbitals of the same energy will have the maximum number of electrons with the same spin. 2p

6. To start we will use orbital filling diagrams to help us with electron configurations….
Example
Boron- has 5 electrons

7. Periodic table arrangement
22/09/99
the quantum theory helps to explain the structure of the periodic table.
n - 1 indicates that the d subshell in period 4 actually starts at 3 (4 - 1 = 3).

9. Order of Electron Subshell Filling: It does not go “in order”
2p6
3s2
3p6
3d10
4s2
4p6
4d10
4f14
5s2
5p6
5d10
5f14
6s2
6p6
6d10
7s2
7p6
1s2
2s2
2p6
3s2
3p6
4s2
3d10
4p6
5s2
4d10
5p6
6s2
4f14
5d10
6p6
7s2
5f14
6d10
7p6

10. Electron Configurations
Element
Configuration
H Z=1
1s1
He Z=2
1s2
Li Z=3
1s22s1
Be Z=4
1s22s2
B Z=5
1s22s22p1
C Z=6
1s22s22p2
N Z=7
1s22s22p3
O Z=8
1s22s22p4
F Z=9
1s22s22p5
Ne Z=10
1s22s22p6
(2p is now full)
Na Z=11
1s22s22p63s1
Cl Z=17
1s22s22p63s23p5
K Z=19
1s22s22p63s23p64s1
Sc Z=21
1s22s22p63s23p64s23d1
Fe Z=26
1s22s22p63s23p64s23d6
Br Z=35
1s22s22p63s23p64s23d104p5
Note that all the numbers in the electron configuration add up to the atomic number for that element. Ex: for Ne (Z=10), = 10

11. Electron Configurations
In the previous slide you will see arrows showing you the direction of the you follow the pattern to fill your electrons. The arrow points at the next highest orbital.
There is also an abbreviated form in which you put the closed noble gas (element on the far right) to the top of the element you are talking about in brackets and then finish the electron configuration from there.
Example: Aluminum: [Ne] 3s2 3p1