1. Electron Configuration

2. Why we study electrons
Knowing the position of electrons helps us with many topics:
Why chemical reactions occur
Why some atoms are more stable than others
Why some elements react with only certain atoms
We want to know how many electrons an atom has, and where they’re located.

3. Electrons Bohr model only begins to explain electrons…
Electrons don’t behave like normal particles. They also act like waves.
Because they act like waves, their exact location around the nucleus cannot be calculated.

4. Electrons Quantum mechanical model of the atom
Electrons are contained in orbitals around atoms. Orbitals are calculated regions of space where there is a high probablility of finding an electron in the atom.
Each orbital can hold 2 electrons
Orbital ≠ Orbit… think firefly

5. Quantum Numbers
There are 4 quantum numbers that describe the energy and approximate position of an electron
Principal Quantum Number (energy level): describes size of orbital
Angular Quantum Number (subshells): describe the shape of the orbital
Magnetic Quantum Number: describes the orientation in space of an orbital (x, y, z-axis)
Spin: clockwise or counterclockwise spin

6. Principal Energy Levels

7. Subshells s-orbital (sphere) p-orbital (peanut)
d- orbital (double peanut)
f-orbital (flower)

8. Periodic Patterns s p d (n-1) f (n-2) 1 2 3 4 5 6 7 6 7
© 1998 by Harcourt Brace & Company

9. Orbital Diagrams
Pathways that show us the order that electrons will fill an atom.
Start from the bottom and work your way up

10. Orbital Diagrams
When working out electron configuration, it’s important to understand orbital diagrams.
Here are 3 rules that will help us understand and interpret orbital diagrams.

11. General Rules Electrons fill the lowest energy orbitals available.
Aufbau Principle
Electrons fill the lowest energy orbitals available.
You cannot skip any orbitals

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

13. General Rules WRONG RIGHT Hund’s Rule
Within a sublevel, place one e- per orbital with the same spin before pairing them.
“Empty Seat Rule”
WRONG
RIGHT

14. A Few more things….
Each arrow you draw represents an electron. (remember the three rules!)
Each orbital holds 2 electrons and has different shapes
The S level has only 1 orbital= total of 2 e-
The P level has 3 orbitals = total of 6 e-
The D level has 5 orbitals = total of 10 e-
The F level has 7 orbitals = total of 14 e-

16. Practice - Fill in the orbital diagram for Magnesium
*Use Smartboard Program for Extra Practice

17. Practice Orbital Diagram WS
Abbreviated orbital diagram (Boxes or dashes)

18. Electron Configuration
An atom’s electron configuration…
Describes the location of electrons within the atom
Identifies the shape of the electron clouds
- regions where the electrons are held.
Uses numbers and letters to describe electrons’ location and which electron cloud it is part of.

19. 1s2 An example The “s” tells you the electron’s cloud shape.
In this case it’s a spherically shaped cloud. It is called the s sublevel. Sublevel = Shape
1s2
The “2” simply tells you how many electrons are in this cloud.
The “1” tells you how far from the nucleus the electrons can go.
In this case 2 electrons are creating the cloud.
In this case, its in the 1st energy level, which is the closest level to the nucleus.
Note: Every orbital can only hold 2 electrons. They must have opposite spins.

20. 1s2 2s2 2p4 O B. Notation 8e- 1s 2s 2p Orbital Diagram
Electron Configuration
1s2 2s2 2p4

21. C. Periodic Patterns Shorthand Configuration
This is a shorter way to do e- configurations
Steps…
1) Write the symbol of the element your doing
2) Find the noble gas (group 8) that comes before the element you are doing.
3) To begin, put that noble gas in [brackets]
4) Starting with that noble gas, finish the electron configuration

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

23. C. Shorthand practice
Example - Germanium
[Ar]
4s2
3d10
4p2

24. Practice these in shorthand
Li N Mg C

25. Draw this! This will help It is a way to remember
the order in which electrons
fill their orbitals.
When you reach the far
Left side, you reach a
“wall” and must go back to
The right hand side.