1. Chapter 5 Modern Atomic Models

2. Bohr’s Atom
Niels Bohr proposed a model of the atom that had electrons circling the nucleus, the ‘Planetary model’
Do you remember how many electrons can fit on each ring?

3. Bohr’s Atom You Try What does a Bohr model for Helium look like?
What about Fluorine?
You try Helium, Oxygen and Potassium

4. Bohr’s Atom cont’d Each ring has a certain energy
These are called ‘Principal energy levels’ (n)
Closer = less energy
Further = more energy

5. Today’s Vocab Words
Principle Energy Level
Sublevel
Orbital

6. Sublevels
For each energy level, we can divide the energy of electrons further into ‘sublevels’ – more on this later
The sublevels are determined by how many orbitals are present
Types of orbitals are s, p, d, f, g…
Principle Energy Level 1 has 1 sublevel (1s)
Principle Energy Level 2 has 2 sublevels (2s and 2p)
Principle Energy Level 3 has 3 sublevels (3s, 3p, 3d)

7. Sublevels You Try
How many sublevels does the 2nd Principle Energy Level have? What are their names?
What about Principle Energy Level 4?
Principle Energy Level 5?

8. Orbitals There is 1 s orbital There are 3 p orbitals
There are 5 d orbitals
There are 7 f orbitals
There are 9 g orbitals

9. Orbitals You Try How many p orbitals are there?
How many f orbitals are there?
How many total orbitals are there in Principle Energy Level 3?

10. Orbitals and Electrons
Each orbital can hold 2 electrons
S orbitals hold 2 electrons
P orbitals hold 6 electrons (3x2=6)

11. Orbitals and Electrons You Try
How many electrons can the 1s sublevel hold?
How many electrons can the 2nd Principle Energy Level hold?
How many electrons can the 2s sublevel hold?
How many electrons can the 3rd Principle Energy Level hold?

12. Bohr’s atom
Start at 5:25

13. Problems with Bohr’s model
Bohr’s model could not explain the differences in energy levels of atoms that were not Hydrogen
We can’t know both the momentum of an electron and its position
Instead we use probability distributions (orbitals)

14. The Quantum Mechanical Model
Atomic orbitals – describe the probability of finding an electron at a certain location

15. Orbitals cont’d
D orbitals (left) and F orbitals (right)

16. Orbital Diagrams: 3 rules
Aufbau principle: Electrons occupy the orbitals of lowest energy first
Lower energy = more stable
Will fill 1 -> 2 -> 3 -> 4 etc…
Will fill s –> p -> d -> f etc…

17. Pauli Exclusion Principle
No two electrons may have the same spin within an orbital
Electrons pair, one has up spin, one has down spin (what does this spin mean? Nothing, we made it up, don’t believe chemists they make up everything)

18. Hund’s Rule
When occupying orbitals, all orbitals must be occupied by electrons of the same spin PRIOR to pairing any electrons
Electrons like their space

19. Lets Try What does an orbital diagram look like for Lithium?
What about Silicon?

20. You Try What does the orbital diagram for Oxygen look like?
What about Potassium?

21. Orbital Diagrams Exceptions
These exceptions occur for metals in the d and f blocks only!
Think of D+1 and F+2
Notable Exceptions:
Fill 4s BEFORE 3d, 5s b4 4d, 6s b4 5d (D+1)
Fill 6s BEFORE 4f, 7s b4 5f (F+2)

22. Remember the Chart or the Exceptions

23. You Try Cont’d What does the orbital diagram for Silver look like?
What about Gold?

24. Electron Configurations? -> EZ
Just take the sublevel, and put a superscript for how many electrons are in that sublevel
For ex, Hydrogen:
1s1
Lithium:
1s22s1

25. You Try What is the electron configuration for Oxygen?
What about Chlorine?