1. Day 2 Quantum Numbers and Electron Configurations
Bono
"The less you know, the more you believe."
Chapter 13
Day 2
Quantum Numbers and
Electron Configurations

2. Models of the Atom
Dalton
Thomson
Rutherford
Bohr

3. Neils Bohr model of the Atom:
Electrons can be in 1 of many “principle energy levels”, but cannot be in between
any of these energy levels.
Each Principle Energy Level (n) is given a number
n=1
n=2
n=3
Electrons move around the nucleus like planets move around the sun.

4. Unfortunately, Bohr’s model of the Hydrogen atom turned out to be incorrect, so a new model was introduced.
But, This!
Not This!

5. What are the Quantum Numbers?
Remember – they give the approximate location of electrons in an atom.
They are actually represented by letters.
N – distance (size of orbital)
l – Shape of orbital
m – orientation in space of orbital
s – spin of the electron

6. Erwin Schrödinger, using complex mathematics, calculated the probability of where an electron is located.
The probability of an electron in the first principle energy level:
An orbital is drawn that encloses the region where the electron is found 90% of the time.

7. First Energy Level (n=1) can contain 1 sublevel orbital
Second Energy Level (n=2) can contain 2 sublevel orbitals
Third Energy Level (n=3) can contain 3 sublevel orbitals and so on…
There are many types of sublevels:

8. Shape
Name
Maximum # of electrons
Lowest
Energy s 2
Spherical p 6
Highest
Energy
Dumbell
Dumbell

9. Maximum # of electrons
Name
Shape
Lowest
Energy d 10 f
Highest
Energy 14 f

10. The next sublevel is g. How many electrons would it hold?
What type of sublevel orbital(s) would be found in the first principle energy level (n=1)? How many electrons will it hold?
What type of sublevel orbital(s) would be found in the second principle energy level (n=2)? How many electrons will it hold?
What type of sublevel orbital(s) would be found in the third principle energy level (n=3)? How many electrons will it hold?

11. 1s vs 2s vs 3s orbitals

12. Called the Pauli exclusion principle
Each sublevel orbital can hold 2 electrons, which have opposite magnetic fields. Therefore, we say that each electron has a spin, which is opposite of each other. This is symbolized by:
Called the Pauli exclusion principle

13. Electron Configurations

14. Electron Configurations
Using quantum numbers to give the arrangement of electrons around the nucleus.
There are three rules that must be followed!

15. Rule #1 AUFBAU principle Electrons fill low energy orbitals first
s,p,d then f
Filling order
1s2s2p3s3p4s3d4p5s4d5p6s4f5d6p7s5f6d7p

16. Rule #2 Pauli Exclusion Principle
Since there are two possible spins for an electron, no more than two electrons may fill an orbital.
Remember: s = 1 orbital, p = 3 orbitals, d = 5 orbitals and f = 7 orbitals

17. Rule # 3
Hund’s Rule
When multiple shapes are present, electrons fill orbitals with parallel spins before pairing up.
Must follow rule #2!
Example 2p

18. Write the following electron configurationsLi Na Be C Si

19. Using the Periodic Table
Read from left to right and top to bottom.
Stop when you:
Reach the end of a row
Change color
Reach the element of interest
Try the following Mg, B, Ne and Cl

20. Short-Cut
Skip back to the previous Noble Gas (core electrons) and start with the element after that.
Try: I, U, Fe