1. Ch. 4.3 Electron Configuration
Atomic Structure

2. POINT > Define electron configuration
POINT > Explain the Aufbau principle
POINT > Explain the Pauli exclusion principle
POINT > Explain Hund’s rule
POINT > Demonstrate 3 methods to indicate electron configuration

3. POINT > Define electron configuration
Review: Recall that electrons in an atom can exist in different main energy levels (principle quantum number) Main energy levels may be divided into sublevels (angular momentum quantum number) A sublevel can contain multiple orbitals (magnetic quantum number) Each orbital can have a maximum of two electrons (spin quantum number)

4. POINT > Define electron configuration
The electron configuration shows where the electrons in an atom are located with respect to the quantum energy levels Three rules guide our understanding of electron configuration…..

5. POINT > Explain the Aufbau principle
1. The Aufbau principle states that electrons occupy the orbitals of lowest energy first Lowest energy levels are (usually) closer to the nucleus

6. POINT > Explain the Aufbau principle

7. POINT > Explain the Aufbau principle
Sublevels within an energy level can overlap sublevels of another principal energy level For example, the 4s orbital is a lower energy level than the 3d orbital

8. POINT > Explain the Aufbau principle

9. WB CHECK: Which shows the order that electrons fill orbitals?
1s  2s  3s  4s  2p  3p  4p  3d 
4d  4p  4s  3d  3p  3s  2p  2s 
1s  2s  2p  3s  3p  4s  3d  4p 
1s  2s  2p  3s  3p  3d  4s  4p 

10. POINT > Explain the Pauli exclusion principle
2. The Pauli exclusion principle: two electrons cannot have the same four quantum numbers
So, two electrons in a single orbital must have opposite spins
Spin is noted as arrows or
when paired

11. POINT > Explain the Pauli exclusion principle
Two electrons cannot have the same four quantum numbers. Example: Two electrons could have main energy level n = 2 and could both be in sublevel p and could both be in orbital px but they would have opposite spin

12. POINT > Explain Hund’s rule
3. Hund’s rule states that within a given sublevel, 1) A single electron goes to each orbital before any pairs are formed 2) The single electrons have the same spin

13. POINT > Demonstrate 3 methods to indicate electron configuration
1. Orbital notation of a hydrogen atom 2. Electron configuration notation: 1s1 1s 2s
2px
2py
2pz 3s

14. POINT > Demonstrate 3 methods to indicate electron configuration
Orbital notation of a lithium atom
E- config: 1s2 2s1 1s 2s
2px
2py
2pz 3s

15. POINT > Demonstrate 3 methods to indicate electron configuration
Orbital notation of a carbon atom:
E- config: 1s2 2s2 2p2 1s 2s
2px
2py
2pz 3s

16. POINT > Demonstrate 3 methods to indicate electron configuration
Orbital notation of an oxygen atom:
E- config: 1s2 2s2 2p4 1s 2s
2px
2py
2pz 3s

17. POINT > Demonstrate 3 methods to indicate electron configuration
Illustrate the orbital notation of a sodium atom
E- config: 1s2 2s2 2p6 3s1 1s 2s
2px
2py
2pz 3s

18. WB CHECK:
What atom is this? 1s 2s
2px
2py
2pz 3s

19. 1s22s22p63s23p4 Show the e- config notation of a sulfur atom:
WB CHECK:
Show the e- config notation of a sulfur atom:
1s22s22p63s23p4
Note: the sum of the superscripts = the number of electrons

20. 1s22s22p63s23p64s23d2 Show the e- config notation of a titanium atom:
WB CHECK:
Show the e- config notation of a titanium atom:
1s22s22p63s23p64s23d2

21. POINT > Demonstrate 3 methods to indicate electron configuration
By convention, after determining electron configuration, we group main energy levels together
(Theory) 1s22s22p63s23p64s23d2
(Actual) 1s22s22p63s23p63d24s2

22. 1s22s22p63s23p5 Show the e- config notation of a chlorine atom:
WB CHECK:
Show the e- config notation of a chlorine atom:
1s22s22p63s23p5

23. WB CHECK:
What atom is this?
1s22s22p63s23p64s23d7
Cobalt

24. POINT > Demonstrate 3 methods to indicate electron configuration
3. Noble gas notation is devised to save time:
Aluminum: 1s22s22p63s23p1
Neon: 1s22s22p6
Aluminum: [Ne]3s23p1

25. POINT > Demonstrate 3 methods to indicate electron configuration
Noble gas notation is devised to save time: Iron: 1s22s22p63s23p63d64s2 Argon: 1s22s22p63s23p6 Iron: [Ar]3d64s2

26. WB CHECK:
Show the noble gas notation of a titanium atom:
[Ar] 4s23d2

27. WB CHECK:
What is this atom?
[Kr] 5s24d9

28. POINT > Define electron configuration
Some configurations differ from those predicted by these rules
Some atoms prefer filled and half-filled sublevels to other configurations (copper & chromium)

29. POINT > Define electron configuration
Ex. Chromium Theoretical: 1s22s22p63s23p63d44s2 Actual: 1s22s22p63s23p63d54s1

30. Homework: Read pages 105-117 Practice #1-2 page 107 Practice #1A, 2-4 Page 115 F.A. #1-5 page 116