1. Chapter 5 Electron Configuration

2. Electrons in Energy Levels
The maximum number of electrons in any energy level is 2n2
Level 2n2 maximum number of electrons
1 2(1)2 2
2 2(2)2 8
3 2(3)
4 2(4)

3. Aufbau Principle
Electrons are “built-up” by filling various energy levels, starting with lower energies, filling orbitals two at a time.
They go into the orbitals one with spin +1/2 ( ), the other with spin - 1/2 ( ).
An orbital diagram is useful in showing this arrangement.

4. Writing Electron Configuration
s orbital = maximum 2 electrons (1 shell)
p orbital = maximum 6 electrons (3 shells)
d orbital = maximum 10 electrons (5 shells)
f orbital = maximum 14 electrons (7 shells)
Electron order determined by the Aufbau diagram (Aufbau = “building up”).

5. Writing Electron Configuration
Aufbau diagram

6. Writing Electron Configuration
Na 11: 1s2
2s2
2p6
3s1
Na 11 :1s22s22p63s1

7. Writing Electron Configuration
Si 14: 1s2
2s2
2p6
3s2
3p2
Si 14: 1s22s22p63s23p2

8. Writing Electron Configuration
Cl 17: 1s2
2s2
2p6
3s2
3p5
Cl 17: 1s22s22p63s23p5

9. Writing Atomic Orbitals
Use the number of electrons to fill in the atomic orbitals for an element:
C 6
1s 2s p 3s p

10. Writing Atomic Orbitals
Use the number of electrons to fill in the atomic orbitals for an element:
Na 11
1s 2s p 3s p

11. Writing Atomic Orbitals
Use the number of electrons to fill in the atomic orbitals for an element:
Si 14
1s 2s p 3s p