1. Electron Configuration

2. Electron Configuration
The way electrons are arranged around the nucleus.

3. Quantum Mechanical Model
1920’s
Werner Heisenberg (Uncertainty Principle)
Louis de Broglie (electron has wave properties)
Erwin Schrodinger (mathematical equations using probability, quantum numbers)

4. Principal Quantum Number, n
What does n represent?
1.)
2.)
Each main energy level has sub-levels

5. Energy Sublevels
s p d f

6. The principle quantum number, n, determines the number of sublevels within the principle energy level.

7. Orbital Quantum Number, ℓ (Angular Momentum Quantum Number)
Indicates shape of orbital sublevels
ℓ = n-1
ℓ sublevel
0 s
1 p
2 d
3 f

8. Orbital
The space where there is a high probability that it is occupied by a pair of electrons.
Orbitals are solutions of Schrodinger’s equations.

9. Orbitals in Sublevels
Sublevel # Orbitals # electrons
s 1
p 3
d 5
f 7

10. Three rules are used to build the electron configuration:
Aufbau principle
Pauli Exclusion Principle
Hund’s Rule

11. Aufbau Principle
Electrons occupy orbitals of lower energy first.

12. Aufbau Diagram

13. -Pauli Exclusion Principle -Electron Spin Quantum Number
An orbital can hold only two electrons and they must have opposite spin.
Electron Spin Quantum Number (ms):
+1/2, -1/2

14. Hund’s Rule
In a set of orbitals, the electrons will fill the orbitals in a way that would give the maximum number of parallel spins (maximum number of unpaired electrons).
Analogy: Students could fill each seat of a school bus, one person at a time, before doubling up.

15. Aufbau Diagram for Hydrogen

16. Aufbau Diagram for Helium

17. Aufbau Diagram for Lithium

18. Aufbau Diagram for Beryllium

19. Aufbau Diagram for Boron

20. Aufbau Diagram for Carbon

21. Aufbau Diagram for Nitrogen

22. Notations of Electron Configurations
Standard
Shorthand

23. Aufbau Diagram for Fluorine

24. Standard Notation of Fluorine
Number of electrons
in the sub level 2,2,5
1s2 2s2 2p5
Main Energy Level Numbers 1, 2, 2
Sublevels

25. Energy Level Filling

26. Filling
Think back to Q.N….this is the reason we had to subtract n in the f & d block.
This will help you when determining e- configuration.

27. Blocks in the Periodic Table

28. Putting It All Together
When writing an e- configuration…do your Aufbau orbital diagram then write out the e- configuration.
Once you have done that, place the sublevels in correct numerical order.

29. Practice
Let’s try some practice with e- configurations

30. Practice Na

31. Practice Cu

32. Practice O

33. Practice Co

34. Practice Ag

35. Shorthand Notation
Based on Noble Gases

36. Shorthand Notation
Use the last noble gas that is located in the periodic table right before the element.
Write the symbol of the noble gas in brackets.
Write the remaining configuration after the brackets.
Ex: Fluorine: [He] 2s2 2p5

37. Practice Cs C Rb