1. The Electron Configuration

2. Understand and illustrate Aufbau, Pauli and Hund rules.
Write the electron configuration of atoms and ions.
Write the valence electron configuration of an atom or ion.

3. Each orientation for a sublevel contains a maximum of 2 e-.
Pauli Exclusion Principle
Electrons are constantly spinning which results in a magnetic field. Two electrons can occupy the same orbital only if they have opposite spins.
Each orientation for a sublevel contains a maximum of 2 e-.

4. Energy Level
Sublevels
Total #
e- capacity 1 s 2
s,p
1+3 = 4 8 3
s,p,d
1+3+5 = 9 18 4
s,p,d,f
= 16 32 n
n types n2
2n2

5. n = 3 1s 2s 2p 3s 3p 3d
n = 2
n = 1

6. Aufbau Principle
Unexcited electrons fill the lowest, most stable, energy orbital available – ground state.
Range of energies contains some overlap between higher principle levels.

7. Electron Configuration
Orbital Box Diagrams 1s 2s 2p 3s 3p 3d 4s

8. Hund rule
Electrons must enter empty orbitals of equal energy first before joining occupied orbitals.

9. Draw orbital box and electron config for carbon.1s 2s 2p 3s 3p 3d 4s
C: 1s2 2s2 2p2
Draw orbital box and electron config for Mg. 1s 2s 2p 3s 3p 3d 4s
Mg: 1s2 2s2 2p6 3s2

10. Draw electron config for germanium.
Ge – atomic number 32
Ge: s2 3d10 4p2
1s2 2s2 2p6 3s2 3p6
[Ar]
Shorthand notation using noble gas “kernels.”
Ge: [Ar] 4s2 3d10 4p2

11. Periodic Table shows orbital filling for the electron configuration of elements.
Energy level (n) of valence electrons is the same as the period of the atom.

13. Use the periodic table to help write the shorthand configurations for Mn and Ag.1 2 3 4 5
Mn: [Ar] 4s2 3d5
Ag: [Kr] 5s2 4d9

14. Valence electrons are the electrons found in the outer-most or highest quantum level (n).
F = 9 electrons
1s2 2s2 2p5
The valence configuration is 2s2 2p5
Ge = 32 electrons
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p2
The valence configuration is 4s2 4p2

15. F- = 9 electrons + 1
1s2 2s2 2p5
The ION configuration is 2s2 2p6
Valence electrons also removed from highest quantum level (n) in positive ions.
Fe+2 = 26 electrons - 2
1s2 2s2 2p6 3s2 3p6 4s2 3d6
The ION configuration is 1s2 2s2 2p6 3s2 3p6 3d6

16. Some exceptions to the rule:

17. Exceptions exist as the energy differences between higher energy sublevels become smaller.
Half-filled and completely filled subshells have extra stability – causes electron promotion.

18. Actual configurations: Cr: [Ar] 4s1 3d5 Cu: [Ar] 4s1 3d10
Electron promotion accounts for multiple ionization states (Fe+2, Fe+3…)