1. Electron Configuration

3. Electron Configuration
Electron configuration is a shorthand notation that shows electron arrangement within orbitals.
Electron configuration can be written in one of 3 methods:
Energy-Level Diagrams (orbital diagram)
Complete electron configuration
Condensed electron configuration (AKA noble gas configuration)

4. Electron Configuration
Principal quantum number “n”
Secondary quantum number “l”

5. Energy Level Diagram

6. Pauli’s Exclusion Principle
No two electron’s have the same 4 quantum numbers
One electron will spin up, the other will spin down
Conventionally we write the electron that spins up first.

7. Aufbau Principle
The number of electrons in an atom is equal to the atomic number
Each added electron will enter the orbitals in the order of increasing energy
Orbitals of lowest energy are filled first
An orbital cannot take more than 2 electrons.
Analogy: You’re very tired after a night out. It’s easier to sleep downstairs on the couch than to climb the stairs to your bedroom. If your friend is already sleeping on the couch, then you will go upstairs.

8. Aufbau Principle

9. Hund’s Rule
Every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied
All electrons in singly occupied orbitals have the same spin.
Analogy: When boarding the bus, you would take an empty seat rather than sit beside someone.

10. Examples
Lithium
Nitrogen
Manganese

11. Electron Configuration for Ions
For anions: add extra electrons
For cations: draw the neutral atom, then subtract the required number of electrons from the orbital with the highest principal quantum number “n”
Examples S2-, Na+, Zn2+

12. Practice
Activity
P. 191 #1-5
P. 194 #6-11

13. Electron Configuration: Finding Trends
Group 1
Group 2
Group 13
Group 14
Group 15
Group 16
Group 17
Group 18
In a chart, write condensed electron configurations and energy level diagrams for the elements in periods 2 and 3.
What patterns do you notice? What generalizations can you make?