1. ELECTRON CONFIGURATION
MAKING SENSE OF THE PERIODIC TABLE

2. Why are electrons so important?
Electrons determine how an atom behaves; what it will or won’t bond with.
Neutral Atoms
Electrons = Negative Protons = Positive
This means that neutral atoms have equal numbers of protons and electrons
So the atomic number not only tells you the number of protons in the atom, but also the number of electrons
EX) How many electrons does a neutral atom of iron have?

3. Layers are called “shells” or “energy levels”
Bohr’s idea of layers
Bohr’s idea that electrons orbit in layers of the atom is very useful to help us visualize the chemistry of atoms.
Think of the layers as “regions” of the electron cloud.
Layers are called “shells” or “energy levels”

4. Electron Configuration
Visualize each energy level split into sub- layers, called “subshells” or “orbitals”
They are named the “s”, “p”, “d”, and “f” orbitals
Each Layer contains certain orbitals
Each orbital can hold a certain number of electrons before it is “full”
s orbital = 2 electrons
p orbital = 6 electrons
d orbital = 10 electrons
f orbital = 14 electrons

5. THE Electron Configuration Hotel
Imagine the atom as a seven-story hotel:
Each floor of the hotel represents a layer of the atom
Each floor has a certain number of rooms
Each room represents an orbital within that layer
Each room type can hold a certain number of guests (s=2, p=6, d=10, f=14)
The number of guests in each room represent the electrons in that orbital

6. The Electron Configuration Hotel Blueprints
7d - 10
7f - 14
6s - 2
6p - 6
6d – 10
6f – 14
5s - 2
5p - 6
5d – 10
5f – 14
4s - 2
4p - 6
4d – 10
4f – 14
3s - 2
3p - 6
3d – 10
Parking Garage
2s - 2
2p - 6
Restaurant
1s - 2
Lobby
Room Types: s (1 bed), p (3 beds), d (5 beds), f (7 beds) – 2 guests per bed

7. Electron Configuration
Sometimes, the orbitals in different layers overlap each other
This causes the orbitals to fill up in a certain order:
Electrons always fill up orbitals of lower energy first.

8. Electron Configuration

9. Why is the periodic table shaped so weird?

10. Electron Configuration
Electron Configuration is a way to mathematically represent an element
Layer (1-7)
Orbital (s, p, d, or f)
Number of Electrons (superscript) (s1-2, p1-6, d1-10, or f1-14)
EX) Hydrogen (atomic # = 1)  1 electron
H: 1s1
EX) Nitrogen (atomic # = 7)  7 electrons
N: 1s22s22p3

11. Electron configuration practice
Sodium (atomic # = 11)
Na: 1s22s22p63s1
Calcium (atomic # = 20)
Ca:1s22s22p63s23p64s2
Bromine (atomic # = 35)
Br: 1s22s22p63s23p64s23d104p5

12. Shows the total number of electrons on each energy level. EX) Boron
Bohr Diagram
Shows the total number of electrons on each energy level.
EX) Boron

13. Be Drawing a Bohr Diagram Draw the Nucleus (element symbol)
Draw the layers
Use the electron configuration
Start filling up the layers with electrons
Follow the electron configuration
EX) Beryllium
Be: 1s22s2 Be

14. Bohr Diagram PRactice
EX) Chlorine
Cl: 1s22s22p63s23p5 Cl

15. Each element has a specific number of valence electrons
Valence Electrons are the electrons located on the outer shell
They are important in determining how elements react with one another

16. Determining the Valence Electrons
A trick to using the periodic table to learn how many valence electrons an element has:
Look at the group number (ones digit)
Group 1 = 1 valence electron
Group 2 = 2 valence electrons
Group 13 = 3 valence electrons
Group 14 = 4 valence electrons
Group 18 = 8 valence electrons
Only used for groups & 13-18
S and P block elements
D and F orbitals are “overlapped” by S and P orbitals

17. Octet Rule
Octet Rule: An atom’s outer shell is full when it has 8 valence electrons
Atoms want a full outer shell (fill s and p orbitals = 8 valence e-)
Noble Gases have 8 valence electrons  they do not react often
Other elements react in order to fill their outer shell
NOTE:
Helium is full with only 2 valence electrons
(s orbital only holds 2)
Periods 4-7 must fill up the previous d/f orbitals
To simplify, we’ll focus on elements 1-18 (periods 1-3)

18. Shows the number of valence electrons
Electron Dot Diagram
Shows the number of valence electrons
Useful in predicting/visualizing chemical bonds
Dots surrounding the element symbol represent valence electrons
If an element is surrounded by 8 valence electrons, it is a noble gas (except helium which only has 2)

19. F Electron Dot Diagram Write the symbol of the element EX) Fluorine
Determine the number of valence electrons
Draw the first two on the right of the symbol
These represent the s orbital – 2
Draw the remaining dots one at a time going counter-clockwise until you finish
top, left, and bottom represent the p orbital – 6
Note, each of the four sides has room for two valence electrons
EX) Fluorine F

20. Electron Dot Diagram
EX) Nitrogen N

21. Electron Dot Diagram
EX) Beryllium Be

22. Putting it All Together
EX) Aluminum
Electron Configuration
1s22s22p63s23p1
Bohr Diagram
Electron Dot Diagram Al Al