1. Quantum Number and Electron Configurations
The arrangement of electrons in an atom

2. Quantum Numbers
Scientists use quantum number to describe the probable region for finding an electron
There are 4 quantum numbers.

3. The Principle Quantum Number
Symbolized by n
Indicates the main energy level occupied the electron (the ring away from the nucleus)
Values of n are positive integers (1,2,3,4)
As n increases, so does the distance from the nucleus as well as the electron’s energy.

4. Angular Momentum Quantum Number
Represented by l
Represents the shape or type of orbital that corresponds to a particular suborbital
Each of these numbers is given a letter. We will only deal with the first four letters.
s, p, d, f

5. Magnetic Quantum Number
Represented by m
Indicates the number and orientations of orbitals around the nucleus
This will tell us how many boxes to make for each type of orbital when completing orbital diagrams
The shapes that result are on Page 96

6. Spin Quantum Number Symbolized by +1/2 and -1/2 or and
Indicates the orientation of the electrons’ magnetic field
Also known as spin

7. How many electrons can each level hold?
The formula used to calculate the number of electrons each level can hold is 2n2
Level # 1 2 3 4 5 6 7
Theoretical 8 18 32 50 72 98
Practical

8. So, those are the Quantum Numbers
But what do they mean?
The answer is in something called electron configurations

9. Aufbau Principle
How did you decide where to send the people at the Hotel Californium?
“Each electron occupies the lowest energy orbital available”
Lowest Energy Highest Energy
s p d f

10. Orbital Filling Sequence and Energy Levels
From Glencoe – Chemistry: Matter and Change

11. Pauli Exclusion Principle
“One person to a bed”
“A maximum of two electrons may occupy a single orbital sublevel, but only if the electrons have opposite spins”

12. Hund’s Rule The Family Situation
“Single electrons with the same spin must occupy each equal-energy orbital before additional electrons with opposite spins can occupy the same orbital.”

13. What does that mean in English?
Much like the family at Hotel Californium, electrons will space each other out as much as possible before occupying spaces close to other electrons.
Here’s another way to think about it:
How do strangers sit on a bus as it fills up?

14. In other words…
SPREAD THEM OUT!!!

15. With all this talk about electrons, here is a review question
With all this talk about electrons, here is a review question? Where can we find out how many electrons an atom has?

16. Now we know the rules and the number of electrons, what do we do with them?

17. Remember this from earlier?
Example: Nitrogen
Electrons? 7
Electron configuration:
1s2 2s2 2p3
Lowest Energy to Highest Energy
From Glencoe – Chemistry: Matter and Change

18. So, if you had the orbital filling sequence, can you fill in the electrons?
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p
Now, let’s take a look at Cl.
Cl has 17 electrons.
Orbital diagram 1s 2s 2p 3p 3s
Writing it without the boxes:
1s2 2s2 2p6 3s2 3p5
Electron Configuration

19. How can I remember all of those numbers and letters?p d f
The Diagonal Rule X 1
2 2 X X 1s 2s
2p 3s
3p 4s
3d 4p 5s X X
4d 5p 6s
4f 5d 6p 7s
5f 6d 7p X X X