1. Electron Configuration
How do you describe the electronic structure of an atom using Lewis dot structures, electron orbital diagrams and electron configuration notations?

2. Valence Electrons
Electrons that are lost/gained or shared when forming bonds
Electrons in the OUTERMOST shell of an atom
Represented in the group number
All elements want 8
Lets take a look…..

3. Lewis Dot structure
1st: determine the elements number of valence electrons
2nd: place dots around the symbol to represent the valence electrons
Ex:
You try: Aluminum
Chlorine

4. Electrons Bohr: placed electrons in energy levels
Energy levels aren’t perfect circles
With in each energy level we can give a more specific location of the electron
Kind of like a street address
Electron configuration: the “exact” location of an electron at a given time

5. Energy levels
Describes the likely position of electrons within the atom
Max # electrons per energy level (shell) = 2(n2), n is energy level
Each Energy level has the same number of sublevels (subshells)

6. So….. How many sublevels would you find in the 1st energy level?
Names?
How many sublevels would you find in the 2nd energy level?
How many sublevels would you find in the 3rd energy level?
How many sublevels would you find in the 4th energy level?

7. Orbitals Each sublevel is divided into specific number of ORBITALS
Each orbital can hold a MAX of 2 electrons
An orbital is represented by a line: 1s __

8. Summary
NOTE: Must fill the NEXT energy levels “s” sublevel PRIOR to filling the CURRENT energy levels “d” sublevel
You must know the following order of electron filling…..
1s22s22p63s23p64s23d104p65s24d10

9. Aufbau Principle
energy levels must be filled from the lowest to the highest and you may not move on to the next level unless the previous level is full.
The first example DOES NOT FOLLOW Aufbau because electrons have been placed in the 3rd energy level before the second was complete
The second example is FOLLOWS Aufbau because the second energy level is full before electrons have been placed in the 3rd energy level.

10. Hund’s Rule
When placing electrons in orbitals, place one electron in each orbital before doubling up
Singly occupy before doubly occupying
The ensures electrons are in order to arrive at the lowest energy configuration
Wrong
RIGHT

11. Pauli Exclusion Principle
States that when electrons do share an orbital, they must be of different “spin.”
Must put one UP arrow & one DOWN arrow in a doubly occupied orbital

12. Identify each error and corresponding rule

13. Configuration and the Periodic Table
Remember: the period numbers refer to the energy levels, so you can write electron configuration like you read a book when looking at the periodic table.

14. Parts of electron Configuration
1 = energy level
S = sublevel
2 = electron in the orbital
1s___
___ = orbital
2 arrows = electron in the orbital

15. Lets Practice: H He Be N Na Al Ca Br

16. Notations: Short Hand Long hand Noble Gas configuration
Ex. 1s22s22p63s2
Long hand
Ex. 1s __ 2s __2p __ __ __
Noble Gas configuration
Ex. [He] 2s22p4