1. Electron Configurations
Chemistry Notes
Electron Configurations

2. Electron Configurations
Studying the arrangement of electrons in atoms helps one understand chemical activity.
From an electron configuration you can determine:
Most stable electron arrangement
Charge
Bonding patterns
Etc.

3. Electron Configurations
Electron Configurations: Shows the Principle Energy Levels, the sublevels and the number of electrons in those sublevels.
Examples of electron configurations:
H  1s1
He  1s2
Li  1s22s1
O  1s22s22p4

4. Electron Configurations

5. Electron Configurations
Rule to remember when writing an electron configuration for a certain atom:
Auf Bau Principle – The lowest energy levels fill first in atoms
Some Energy Levels do overlap
In atoms a 4s level will fill before a 3d level because the 4s sublevel has a lower energy than the 3d.

6. Electron Configurations
Notice: the 4s is lower in energy than the 3d sublevel, therefore, it fills first.

7. Electron Configurations
Start at the top of the arrow, go down. Once you are at the head of the arrow go to the top of the next. Repeat until you have reached the desired number of electrons.
Using this diagram can help you understand how to write the correct electron configuration for each atom.

8. Electron Configurations
EX: Ag has 47 electrons
Fill sublevels until they add up to 47.
Remember how many electrons can go in each sublevel.
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d9
s = 2
p = 6
d = 10
f = 14
Notice: the last sublevel only contains 9 (not 10) electrons

9. Electron Configurations
Another Ex:  Titanium has 22 electrons
Ti: 1s2 2s2 2p6 3s2 3p6 4s2 3d2

10. Electron Configurations
Here is a similar diagram for EC

11. Electron Configurations
EC can be abbreviated  a noble gas configuration (seen below).
Element Z
Electron Configuration
Noble Gas Configuration
Scandium 21
1s2 2s2 2p6 3s2 3p6 4s2 3d1
[Ar] 4s2 3d1
Titanium 22
1s2 2s2 2p6 3s2 3p6 4s2 3d2
[Ar] 4s2 3d2
Vanadium 23
1s2 2s2 2p6 3s2 3p6 4s2 3d3
[Ar] 4s2 3d3
Notice: [Ar] represents the EC of Argon

12. Orbital Filling Diagrams
An orbital diagram gives more detailed information than an electron configuration.
Boxes or blanks are used to represent orbitals.
Arrows represent electrons.
Upward-pointing arrows represent electrons with +1/2 spin
Downward-pointing arrows represent electrons with -1/2 spin
Like EC but arrows are used instead of #’s

13. Orbital Filling Diagrams

14. Orbital Filling Diagrams
Rules to remember when writing an orbital filling diagram for a certain atom:
Hund’s Rule – each orbital gets one electron before any get two
EX: Nitrogen  each 2p orbital gets on e- before any get 2 e-.

15. Orbital Filling Diagrams
Hund’s Rule (cont.)
Notice that the 2p electrons are shown as…
rather than.
This is WRONG!!!

16. Orbital Filling Diagrams
Rules to remember when writing an orbital filling diagram for a certain atom:
Pauli Exclusion Principle – electrons in the same orbital must spin opposite directions.
This is why one arrow is drawn up and one is drawn down.

17. Orbital Filling Diagrams
Examples of An Orbital Filling Diagrams

18. OFD and EC

19. Summary Be able to… Explain what EC and OFD are Write and EC
Recall the Auf Bau Principle
Write and OFD
Recall Hund’s Rule
Recall the Pauli Exclusion Principle