1. Quantum Numbers and Writing Electron Configurations
Electrons in Atoms
Quantum Numbers and Writing Electron Configurations

2. Quick Review - Nucleus Nucleus concentrated mass of p+ & n0
held together by the strong force
Thomson & Rutherford’s experiments

3. Quick Review - Electrons
The Bohr Model of the Atom
electrons orbiting the nucleus much like planets orbiting the sun - WRONG
(electrons are more like bees around a hive)
Electrons are in certain energy states

4. Quick Review - Electrons
Schrodinger – quantum mechanical model of the atom
Atomic orbitals describe the electron’s probable location

5. Arrangement of Electrons
Quantum numbers
Specify the “address” of each electron in an atom
UPPER LEVEL

6. Quantum Numbers Principal Quantum Number ( n ) Principle Energy level
Size of the orbital

7. Quantum Numbers f d s p Energy sublevels Shape of the orbital
Principle energy level 1 has 1 sublevel, principle energy level 2 has 2 sublevels,… f d s p

8. Quantum Numbers
Within each sublevel you have orbitals

9. Relative sizes of the spherical 1s, 2s, and 3s orbitals of hydrogen.

10. The three 2p orbitals.

11. The shapes and labels of the five 3d orbitals.

12. Quantum Numbers 2s 2px 2py 2pz
Orbitals combine to form a spherical shape. 2s
2pz
2py
2px

13. Quantum Numbers n = # of sublevels per level
n2 = # of orbitals per level

14. How principal levels can be divided into sublevels.

15. Principal level 2 shown divided into the 2s and 2p sublevels.

16. Energy Levels, Sublevels, Orbitals, Electrons
Sublevels in
main energy
level
(n sublevels)
Number of
orbitals per
sublevel
Electrons
per sublevel
electrons per
level (2n2) 1 s 2 p 3 6 8 d 5 10 18 4 f 7 14 32

17. Writing Electron Configuration
Electrons in Atoms
Writing Electron Configuration

18. Electron Configurations
No two electrons in an atom can have the same 4 quantum numbers.
Each e- has a unique “address”: 
energy level
sublevel (s,p,d,f)
orbital
electron

19. General Rules Aufbau Principle
Electrons fill the lowest energy orbitals first.
“Lazy Tenant Rule”

20. Filling Orbitals

21. General Rules Pauli Exclusion Principle
Each orbital can hold TWO electrons with opposite spins.

22. General Rules WRONG RIGHT Hund’s Rule
Within a sublevel, place one e- per orbital before pairing them.
“Empty Bus Seat Rule”
WRONG
RIGHT

23. Notation C 1s 2s 2p Orbital Diagrams a box for each orbital
An arrow for each electron
Label each box with principle quantum number and sublevel
Example:
orbital diagram for a ground state carbon atom C 1s 2s 2p

24. Orbital Diagram

25. Orbital Diagrams

26. 1s2 2s2 2p4 O Notation 1s 2s 2p 8e- Orbital Diagram
Electron Configuration
1s2 2s2 2p4

27. Notation Practice
Write the orbital diagrams and electron configurations for the following ground state atoms:
Lithium
Fluorine

28. S 16e- 1s2 2s2 2p6 3s2 3p4 S 16e- [Ne] 3s2 3p4 Notation Core Electrons
Longhand Configuration
S 16e-
1s2
2s2
2p6
3s2
3p4
Core Electrons
Valence Electrons
Shorthand Configuration
S 16e- [Ne] 3s2 3p4

29. Notation Practice
Write the shorthand (noble gas) electron configuration for the following atoms:
Sodium
Selenium
Na [Ne] 3s1
Se [Ar] 4s2 3d10 4p4

30. Order of Filling Orbitals

31. Orbitals being filled for elements in various parts of the periodic table.

32. CONGRATULATIONS! WOW! We sure covered a lot of territory!
You have finished a very difficult, but important,
chapter in Chemistry.
CONGRATULATIONS!

33. Review your notes & do practice problems!
Feeling overwhelmed?
Review your notes & do practice problems!