1. Section 4.3—Electron Addresses
The Electron Hotel-a relatively reasonable analogy.

2. Electron Configurations.
The purpose of this tutorial is to help you understand how electrons are arranged in their energy levels. You will learn how to write electron configurations, and how these electron arrangements relate to the shape and lay-out of the periodic table.
Because electrons are so important in chemistry, the way in which they are arranged around the nucleus plays a crucial role in determining the chemical reactivity of all the elements.

3. First let’s review a little:
As we have learned, electrons exist in very specific energy levels.
And when these electrons absorb energy…
They get energized up to higher levels.
Actually, the jump to higher levels is not a gradual transition as was just shown.
It is a “quantum” jump, and looks more like this:
Quantum means it happens all at once – instantaneously – because the electron can never exist between levels – not even for a second.

4. Once it is at this higher level (excited state), it doesn’t stay there long.
It quickly drops down to a lower level – again as a quantum leap – and as it does, it gives off a distinct band of light energy.
Also, notice how the electron doesn’t have to drop all the way back down to the lowest level. It can get energized up to any level, and from there it can drop to any lower level. AND the different drops each produce different frequencies of light.
And a 5  2 drop produces violet light
See how an electron dropping from the 3rd level to the 2nd level produced red light
A 4  2 electron drop produces blue light

5. The story of the Electron Hotel
Parking Garage
Shopping Center
Restaurant
A man built a hotel for electrons with a restaurant next door.
But he was making so much money that he decided to add on with some more rooms and a parking garage.
He still had high demand and decided to add on some more rooms and a shopping center.
He used the last space he could to put some rooms above the shopping center.

6. How the Electron Hotel Fills
Restaurant
Shopping Center
Parking Garage
This man had some very strange ideas about how to run his hotel. He insisted four things:
The lowest possible floor must be used first
There can only be one person in a room until all the rooms at that level have one person.
No more than 2 people to a room
When two people are in a room, they must be of opposite sex
If 8 people come to the hotel, where would he put them?

7. Another Example Shopping Center Parking Garage Restaurant
This man had some very strange ideas about how to run his hotel. He insisted four things:
The lowest possible must be used first
There can only be one person in a room until all rooms at that level have someone
No more than 2 people to a room
When two people are in a room, they must be of opposite sex
If 21 people come to the hotel, where would he put them?

8. Where are electrons really located? In Electron Clouds!
Electron Hotel
Which section of the hotel
Which floor
Which room
The electron cloud is made of energy levels
Principal energy levels
Subshells
Energy levels are composed of subshells
Orbitals
Subshells have orbitals.

9. Subshell versus Orbital
Subshell – A set of orbitals with equal energy (A set of rooms on the same floor)
Orbital – Area of high probability of the electron being located.
Each orbital can hold 2 electrons

10. What do the orbitals “look” like?
The Orbitals are actually probability regions.
The Orbitals aren’t visible. It is as if the electron has a force field that keeps it in that space.
Here are the “shapes” of the S and P subshells:
Looks like a dumbbell
Looks Spherical
Draw an example of each type of orbital in your notes now.

12. Number of equal energy orbitals Total number of electrons possible
Types of Subshells
Subshell
Begins in energy level
Number of equal energy orbitals
Total number of electrons possible s 1 1 2 p 2 3 6
Energy increases d 3 5 10 f 4 7 14
Some people do find good health ---- a quick way to remember subshell order!

13. What are electron configurations?
Think of it as an energy address for your electron!
Electron configurations use boxes for orbitals and arrows for electrons.

14. Energy and Subshells 6p 5d 4f 6s 5p 4d 5s 4p 3d 4s 3p 3s 2p
Subshells are filled from the lowest energy level to increasing energy levels. 2s
Energy
Does this look familiar? Electron Hotel! 1s

15. Aufbau Principle
The first of 3 rules that govern electron configurations
Aufbau Principle: Electrons must fill the lowest available subshells and orbitals before moving on to the next higher energy subshell/orbital. 1
Where did we see this “rule” in the Electron Hotel?

16. Auf Bau Filling Scheme
This scheme follows the filling order rules you JUST learned but it puts it in an easy to use and easy to remember format!
Total # electrons

17. Hund’s Rule
Hund’s Rule: Place electrons in unoccupied orbitals of the same energy level before doubling up. 2
How does this work?
If you need to add 3 electrons to a p subshell, add 1 to each before beginning to double up.
Where did we see this “rule” in the Electron Hotel?

18. Pauli Exclusion Principle
Pauli Exclusion Principle: Two electrons that occupy the same orbital must have different spins. 3
“Spin” is designated with an up or down arrow.
How does this work?
If you need to add 4 electrons to a p subshell, you’ll need to double up. When you double up, make them opposite spins.
Where did we see this “rule” in the Electron Hotel?

19. Determining the Number of Electrons
Charge = # of protons – # of electrons
Atomic number = # of protons
Example:
How many electrons does Br-1 have?

20. Determining the Number of Electrons that you will configure or address
Charge = # of protons – # of electrons
Atomic number = # of protons
Example:
How many electrons does Br-1 have?
Charge = -1
Atomic number for Br = 35 = # of protons
-1 = 35 - electrons
Electrons = 36

21. Writing Electron Configurations
Example:
Write the boxes & arrows configuration for Cl

22. Electron Configurations
Shorthand way of showing the Box diagram configurations
The number of electrons in a subshell are shown as a superscript after the subshell designation 1s 2s 2p 3s 3p
1s2 2s2 2p6 3s2 3p5

23. Writing Electron Configurations:1
Determine the number of electrons to place 2
Follow Aufbau Principle for filling order
Fill in subshells until they reach the desired number of electrons. Remember the maxs are (s = 2, p = 6, d = 10, f = 14). 3
The total of all the superscripts is equal to the number of electrons. 4
Example:
Write the electron configuration for S
No charge written  Charge is 0
Atomic number for S = 16 = # of protons
0 = 16 - electrons 1s 2s 2p 3s 3p 2 2 6 2 4
Electrons = 16 2 + 2 + 6 + 2 + 4 = 16

24. Writing Electron Configurations using Box Diagrams!
Example:
Use box diagrams to determine the electron configuration for Cl
No charge written  Charge is 0
Atomic number for Cl = 17 = # of protons
0 = 17 - electrons
Electrons = 17 4 9 7 5 6 12 11 10 2 3 5 1 1s 2s 2p 3s 3p

25. Electron Configuration
1s1
group #
# valence e-
possibilities are:
s: 1 or 2
p: 1-6
d: 1-10
f: 1-14
Total e- should equal
Atomic #
row #
shell #
possibilities are 1-7
7 rows
subshell
possibilities are
s, p, d, or f
4 subshells
What element has an electron configuration of 1s1?

26. s p d f 1 2 3 4 5 6 7 1A 2A 3B 4B 5B 6B 7B 8B 1B 2B 3A 4A 5A 6A 7A 8A
group # = # valence (outside) e- s 1 2 3 4 5 6 7 p
Row =
# shells d f

27. Subshells d and f are “special”
group # = # valence e- 1 2 3 4 5 6 7 3d d
period # = # e- shells 4d 5d 6d f 4f 5f

28. Noble Gases & Noble Gas Notation
Noble Gas – Group 8 of the Periodic Table. They contain full outer electron or valence shells.
Noble Gas Notation – used to represent the core (inner) electrons and only the valence shell is shown. Br
Full Configuration 1s 2s 2p 3s 3p 2 6 4s 3d 10 4p 5
Noble gas
[Ar] 4s 2 3d 10 4p 5
The “[Ar]” represents the core electrons and only the valence electrons are shown

29. Noble Gas Notation Example1
Determine the number of electrons to place 2
Determine which noble gas to use
Start where the noble gas left off and write the electron configuration for the valence electrons remaining 3
Example:
Write noble gas notation for As

30. Noble Gas Notation Example1
Determine the number of electrons to place 2
Determine which noble gas to use
Start where the noble gas left off and write spectroscopic notation for the valence electrons 3
No charge written  Charge is 0
Example:
Write noble gas notation for As
Atomic number for As = 33 = # of protons
0 = 33 - electrons
[Ar] 4s 3d 4p 2 10 3
Electrons = 33 18 + 2 + 10 + 3 = 33
Closest noble gas: Ar (18)
Ar is full up through 3p

31. Practice: Ask these questions every time you have to write an electron configuration
Lithium:
find the element on the periodic table
what is the period number?
how many shells?
what is the group number?
how many valence electrons?
what subshell(s) does Li have?
what is the electron configuration?
atomic # = 3 2 2 1 1 s
1s2 2s1

32. Practice: Ask these questions every time you have to write an electron configuration
Boron:
find the element on the periodic table
what is the row #?
how many shells?
what is the group #?
how many valence electrons?
what subshell(s) does B have?
what is the electron configuration?
atomic # = 5 2 2 3 3 p
1s2 2s2 2p1