1. 𝑭𝒐𝒓𝒄𝒆=𝒌 𝒒 𝟏 𝒒 𝟐 𝒓 𝟐 Bohr Model (Shell Model)
Evidence suggested electrons occupied specific energy levels (shells) while “orbiting” around nucleus
Essentially based on Coulomb’s Law
k = coulomb’s constant
q = object with a charge
r = radius (distance between the 2 charged particles)
𝑭𝒐𝒓𝒄𝒆=𝒌 𝒒 𝟏 𝒒 𝟐 𝒓 𝟐
Was used to help explain why electrons didn’t come “crashing” into the nucleus (since opposites attract)
Attractive force between nucleus and electron is balanced by electron’s centrifugal force
The Bohr model makes great predictions BUT there’s a couple things about electrons we discovered:
Uncertainty
Electron spin

2. Orbital Electrons have a Spin Uncertainty: We can never know BOTH the:
- Heisenberg Uncertainty Principle
We can never know BOTH the:
Location of an electron
Momentum of an electron
Because of this, we realized that electrons live in these “clouds” of probability
Don’t follow specific orbits
Orbital
Where electrons spend their time
Electrons have a Spin
Clockwise or counter-clockwise magnetic spin
As a result of this electron spin:
Only two (max) electrons can exist in an orbital
This forced us to modify our “shell” (Bohr) model in order to better align with the evidence of reality
Quantum mechanical model of the atom
Computers allowed us to complete complex equations and software to predict how atoms are going to interact

3. Orbitals s orbital d orbitals p orbitals f orbitals
ALL of these orbitals simply represent “clouds” of probability where electrons sit
p orbitals
f orbitals

4. Quantum Numbers Size (n) Shape (l) Orientation (ml) Spin (ms)
Size of the orbital
As n gets larger then the area in which the electron occupies gets larger as well
These numbers allow us to predict WHERE electrons are most likely to be found which allows us to predict:
What an atom looks like
How atoms are going to interact
Shape (l)
Shape of the orbital
Can be either an s, p, d, f
Orientation (ml)
Tells us the number of orientations the orbitals can have
s orientation
p orientations
d orientations
f orientations
Spin (ms)
Clockwise (+1/2)
Counter-clockwise (-1/2)
Dictates that only 2 electrons can exist in an orbital

5. Electron Configuration
Distribution of electrons
Where the electrons are found in atoms OR in ions
Ionization energy
Amount of energy it takes to remove an electron
Can be quantified using Coulomb’s Law
Multielectron atoms or ions
Shells, subshells, and orbitals similar ionization energy
Nucleus
Core electrons
Valence electrons
shield

6. hydrogen Atomic number Each box represents and orbital
Each arrow represents an electron

7. helium Atomic number Each box represents and orbital
Each arrow represents an electron

8. lithium Atomic number Each box represents and orbital
Each arrow represents an electron

9. beryllium Atomic number Each box represents and orbital
Each arrow represents an electron

10. boron Atomic number Each box represents and orbital
Each arrow represents an electron

11. carbon Atomic number Each box represents and orbital
Each arrow represents an electron

12. nitrogen Atomic number Each box represents and orbital
Each arrow represents an electron

13. oxygen Atomic number Each box represents and orbital
Each arrow represents an electron

14. fluorine Atomic number Each box represents and orbital
Each arrow represents an electron

15. neon Atomic number Each box represents and orbital
Each arrow represents an electron

16. sodium Atomic number Each box represents and orbital
Each arrow represents an electron

17. magnesium Atomic number Each box represents and orbital
Each arrow represents an electron

18. Periodicity 1s1 hydrogen 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f

19. Periodicity 1s22s22p1 boron 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f

20. Periodicity 1s22s22p6 neon 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f

21. Periodicity 1s22s22p63s1 sodium 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f

22. Periodicity 1s22s22p63s23p64s23d4 chromium [Ar]4s23d4 1s 2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d
7s 7p
chromium
1s22s22p63s23p64s23d4
Same thing
[Ar]4s23d4