1. Section 4: Electron Configurations

2. 2s 2p 1s 3s Electron energy levels have sublevels of different shapes
orbital
Nucleus 2p
orbitals 1s
orbital 3s
orbital

3. How do electrons fill these orbitals?
Electron Configurations:
location of e–’s in different orbitals
3 principles
Describe the
electron configuration
of any atom:
the aufbau principle
the Pauli exclusion principle
and Hund’s rule

4. This aufbau diagram shows the energy levels of the various atomic orbitals. Orbitals of greater energy are higher on the diagram. Using Tables Which is of higher energy, a 4d or a 5s orbital?
Aufbau Principle
(building up), electrons fill the orbitals of lowest energy first.

5. ↑ ↓ s Pauli Exclusion Principle
an atomic orbital may describe at most two electrons that must have opposite spins; that is, the electron spins must be paired. ↑ ↓ s

6. ↑ ↓ ↑ ↓ ↑ ↓ px py pz Hund’s Rule
electrons occupy orbitals of the same energy with as many of the same spin as possible before opposite spin. ↑ ↓ ↑ ↓ ↑ ↓ px py pz

7. Electron configuration
Element
# of electrons
Orbital notation
Electron configuration
Lithium 3
____ ____ ____ ____ ____
1s s p
1s22s1
Beryllium 4
1s22s2
Boron 5
1s22s22p1
Carbon 6
1s22s22p2
Nitrogen 7
1s s p
1s22s22p3
Oxygen 8
1s22s22p4
Fluorine 9
1s22s22p5
Neon 10
1s22s22p6

8. Write the electron configuration for phosphorus (P):
nucleus

9. 1s2 2s2 2p6 3s2 3p3 valence electrons:
Write the electron configuration for phosphorus (P):
1s2
2s2
2p6
3s2
3p3
valence electrons:
e–’s in the outer most (highest) energy level
How many valence e–’s in phosphorus (P)? 5
nucleus

10. Write the electron configuration for Krypton (Kr):
1s2
2s2
2p6
3s2
3p6
4s2
3d10
4p6
-Where should we start placing electrons first? -Opposite spin alleviates repulsion. -All single before double.
nucleus

11. valence electrons: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6
Write the electron configuration for Krypton (Kr):
1s2
2s2
2p6
3s2
3p6
4s2
3d10
4p6
valence electrons:
e–’s in the outer most (highest) energy level
-Where should we start placing electrons first? -Opposite spin alleviates repulsion. -All single before double.
How many valence e–’s in Krypton (Kr)? 8
nucleus

12. Quick Quiz!
1. Identify the element that corresponds to the following electron configuration: 1s22s22p63s2 Ca Ne Na Mg

13. Quick Quiz.
2. Write the electron configuration for the atom N.
1s22s22p5
1s22s22p3
1s22s1p2
1s22s22p1

14. Quick Quiz.
3. What is the first (lowest-numbered) principal energy level in which p orbitals are found? 1 2 3 4

15. Electron Configurations and the Periodic Table
The period number tells you the energy level (remember, the d block is one energy level lower).
The group # tells you the # of valence electrons.
Group 1 elements have 1.
Group 7A have 7.

16. Noble Gas Core Configuration
Noble Gases are group 18
Na:
1s2
2s2
2p6
3s1
Ne:
1s2
2s2
2p6
Noble gas e- config for Na:
[Ne]
3s1 Ne

17. Write the full electron configuration for Gallium (Ga), atomic number 31.
1s2
2s2
2p6
3s2
3p6
4s2
3d10
4p1
[Ar]
4s2
3d10
4p1 OR Ar

18. P Lewis dot diagrams valence e–’s are shown as dots around
the symbol of the element
Phosphorus (P):
1s2 2s2 2p6 3s2 3p3
# valence e–’s: ___ 5
[Ne]3s2 3p3
Group # : ___ 5A
Lewis dot diagram: P

19. Br Lewis dot diagrams valence e–’s are shown as dots around
the symbol of the element
Bromine (Br):
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
[Ar]4s2 3d10 4p5
# valence e–’s: ___ 7
Group # : ___ 7A
Lewis dot diagram: Br