1. 4.3 Electron Structure
Adapted from Kelly Deter’s Chemistry You Need to Know

2. Bohr Model Revisited-convenient way to show electrons in energy levels
It consists of the nucleus with protons & neutrons and electrons in concentric orbits (circles) outside the nucleus
The circle closest to the nucleus contains the lowest energy electrons
The 1st level can hold a max. of 2 electrons, the 2nd level can hold a max. of 8 electrons, the 3rd can hold a maximum of 18, and the 4th level a maximum of 32.
BE CAREFUL: At first, only 8 electrons enter the 3rd block, then 2 in the 4th and then any other remaining will enter back into the 3rd energy level. (This will be explained later.)

3. Bohr Model Revisited-convenient way to show electrons in energy levels
If electrons want to move to a higher energy level, they have to GAIN energy!
If electrons want to move to a lower energy level, they have to LOSE energy!

4. Pictures of the Bohr Models
Electron
Proton
Neutron
Hydrogen-1
Helium-4
Lithium-6
1 p 0 n 1 e p 2 n 2 e p 4 n 3 e

5. Examples Draw Bohr model diagrams for the following elements.
Nitrogen= __e- Magnesium=__e Iron=__e-

6. Electron Hotel f Tower Seven rooms per floor d Tower
Floor 3 CLOSED
Floor 2 CLOSED
Floor 2 CLOSED
The electron hotel is adapted from Kelly Deter’s revised PowerPoint presentation for Chemistry You Need to Know Chapter 4, section 3
Floor 1 CLOSED
f Tower
Seven rooms per floor
Floor 1 CLOSED
d Tower
Five rooms per floor
Floor 1 CLOSED
p Tower
Three rooms per floor
s Tower
One room per floor

7. Electron Hotel
The hotel is also built on a hill. As you can see, the first floor of f Tower is higher than the first floor of d Tower, which is higher than the first floor of p Tower, etc.
It is also important to note that the hill is so steep, the 3rd floor of d Tower is actually between the 2nd floor of s Tower and the 2nd floor of d Tower. The f tower has a similar structure
Please note that the lower floors of some towers are closed, so they cannot be filled (actually they were never even built ).

8. Electron Hotel There are some physical restrictions of the rooms.
Each room has two single beds, a top bunk (represented by an up arrow) and a bottom bunk (represented by a down arrow).
The Electron Hotel is managed by three basic rules. As the guests come in they are placed in rooms based only on these rules, so as the hotel fills, it always follows the same pattern.
Watch the following animation silently and see if you can figure out the three rules.

9. Electron Hotel f Tower Seven rooms per floor d Tower
Floor 3 CLOSED
Floor 2 CLOSED
Floor 2 CLOSED
It would be helpful to narrate the filling of “rooms” by announcing the “Tower”, (s, p, d, f) “Floor”, (1, 2, 3, etc) and “Bunk” (top or bottom), as they are filled
Floor 1 CLOSED
f Tower
Seven rooms per floor
Floor 1 CLOSED
d Tower
Five rooms per floor
Floor 1 CLOSED
p Tower
Three rooms per floor
s Tower
One room per floor

10. Rule 1 People MUST be placed in rooms on the lowest floor available
note again that the lowest floor built for the p Tower is floor 2, the lowest for d Tower is floor 3 and the lowest for f Tower is floor 4
Also remember that floor 3 for the d Tower is actually higher up than floor 4 for the s Tower but lower than floor 4 for the p Tower.

11. Electron Hotel f Tower Seven rooms per floor d Tower
Floor 3 CLOSED
Floor 2 CLOSED
Floor 2 CLOSED
Narrate the principal energy levels and subshell as they fill
Floor 1 CLOSED
f Tower
Seven rooms per floor
Floor 1 CLOSED
d Tower
Five rooms per floor
Floor 1 CLOSED
p Tower
Three rooms per floor
s Tower
One room per floor

12. Rule 2
A room may have a maximum of two people in it, and when two people are in the same room, they are ALWAYS in separate bunks, one in the top bunk, one in the bottom bunk.
The employees also will fill the top bunk before filling the bottom bunk.

13. Electron Hotel f Tower Seven rooms per floor d Tower
Floor 3 CLOSED
Floor 2 CLOSED
Floor 2 CLOSED
Floor 1 CLOSED
f Tower
Seven rooms per floor
Floor 1 CLOSED
d Tower
Five rooms per floor
Floor 1 CLOSED
p Tower
Three rooms per floor
s Tower
One room per floor

14. Rule 3
When a tower has more than one room per level, you must put one person in each room before putting two people in any of the rooms on that floor

15. Electron Hotel f Tower Seven rooms per floor d Tower
Floor 3 CLOSED
Floor 2 CLOSED
Floor 2 CLOSED
Floor 1 CLOSED
f Tower
Seven rooms per floor
Floor 1 CLOSED
d Tower
Five rooms per floor
Floor 1 CLOSED
p Tower
Three rooms per floor
s Tower
One room per floor

16. The rules
Fill all rooms on the lowest available floor before putting anyone in a room on a higher level floor.
Each room can have a maximum of two people, and when two people are in the same room, one must be in the top bunk, the other in the bottom bunk.
When a floor has more than one room, each room must have one person in it before putting a second person in any of them.

17. Electron Hotel f Tower Seven rooms per floor d Tower
Floor 3 CLOSED
Floor 2 CLOSED
Floor 2 CLOSED
Narrate “1s up, 1s down, 2s up, 2s down, 2p up, 2p up, 2p up, 2p down, 2p down, 2p down, 3s up, 3s down”
Floor 1 CLOSED
f Tower
Seven rooms per floor
Floor 1 CLOSED
d Tower
Five rooms per floor
Floor 1 CLOSED
p Tower
Three rooms per floor
s Tower
One room per floor

18. Assign 26 guests to the Electron Hotel
Floor 3 CLOSED
Floor 2 CLOSED
Floor 2 CLOSED
It would be helpful to narrate the filling of “rooms” by announcing the “Tower”, (s, p, d, f) “Floor”, (1, 2, 3, etc) and “Bunk” (top or bottom), as they are filled
Floor 1 CLOSED
f Tower
Seven rooms per floor
Floor 1 CLOSED
d Tower
Five rooms per floor
Floor 1 CLOSED
p Tower
Three rooms per floor
s Tower
One room per floor

19. Atoms are NOT hotels
Electrons, of course, are really in the electron cloud of an atom, not in a hotel, but the rules we learned still apply.
The rules are based on energy and stability, not on some arbitrary rules some hotel manager came up with.

20. Translations Hotel The electron cloud
Where all electrons in an atom are located
Floor
Principal energy level
How far an electron is from the nucleus and how much energy it has – designated 1, 2, 3, etc
Tower
subshell
Some energy levels have more than one subshell – the higher the principal energy level, the more subshells it can have
Room
Orbital
The higher the energy of the subshell (within the same principal energy level) the more orbitals it has, and the more complex the orbital shapes are
Bunk
Spin
The spin is the angular momentum of the electron. If two electrons occupy the same orbital, they must have opposite angular momentum.

21. Details
An electron cloud describes the area where the electrons of an atom are likely to be. It includes all subshells and orbitals
A subshell is a set of orbitals with equal energy
An orbital is an area of high probability of the location of the electron
There is always some uncertainty

22. Electron Configurations
What is an electron configuration?
It shows the position and grouping of electrons in an atom
The position and grouping of electrons in an atom determine when and how it can glow.
Chemical properties of elements are closely related to the arrangement of their electrons
Several ways to write electron configurations
Orbital notation (shows the most detail)
Full electron configuration (standard notation)
Noble gas configuration (a shorthand of the standard)

23. 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

24. Subshells!
As noted before, the higher the principal energy level the more subshells it can have.
Level 1 only has 1 subshell: s
Level 2 can have 2 subshells: s and p
Level 3 can have 3 subshells: s, p and d
Level 4 can have 4 subshells: s, p, d and f
Level 5 can have 5 subshells: s, p, d, f and “g”
No element that has been discovered to occur naturally, and no element that has been made in a laboratory has a g subshell in the ground state

25. Rules Review and Translation
Aufbau Principle (rule 1 in the hotel)
Pauli Exclusion Principle (rule 2 in the hotel)
Hund’s Rule (rule 3 in the hotel)

26. Rule 1/Aufbau Principle
Electrons fill subshells so that the total energy of the atom is minimum.
What does this mean?
This means you fill the lowest energy subshells first, and that a subshell must be completely full before beginning to fill any higher energy subshells.
The word aufbau comes from a German word that means “building up”. You “build up” the electrons from low energy to higher.

27. Rule 2/Pauli Exclusion Principle
Two electrons that occupy the same orbital must have opposite spins.
What does this mean?
As you fill the electrons, whenever one orbital has two electrons, there must be one with positive spin (up arrow) and one with negative spin (down arrow).
We always fill the up arrow first, and the down arrow second

28. Rule 3/Hund’s Rule
Place electrons in unoccupied orbitals of the same energy before placing a second electron in an already occupied orbital.
What does this mean?
Fill all positive spin electrons (up arrows) in a subshell before putting any negative spin electrons (down arrows)
and remember you can’t have two “positive spins” in the same orbital
As a convention, we always fill the orbitals from left to right (within the same subshell).

29. Number of electrons
No matter what type of electron configuration you are showing, you must first determine the number of electrons in the atom
This is very simple for a neutral atom
# electrons = # protons = atomic number!
For an ion it only requires a little math
Charge = # protons − # electrons, so
# electrons = # protons – charge
Watch out for negative charges!!!!!

30. Orbital Notation Determine the number of electrons
Draw all the boxes for a subshell when you add the first electron in that subshell (we name only subshells).
The name of a subshell is the principal energy level and the subshell.
Example an electron in an orbital of the p subshell in the 3rd principal energy level would be in the “3p”
subshells are individually drawn starting from the left and moving to the right.
How many orbitals (drawn as boxes)?
s subshell has one, p has 3, d has 5, f has 7
Follow Aufbau Principle, Pauli Exclusion Principle and Hund’s Rule to fill in the electrons.

31. Example – Draw the orbital notation for chlorine
Determine the number of electrons.
Since there is no charge indicated, the atom must be neutral.
# electrons = # protons = Atomic Number
Atomic number is 17, so…
there are 17 electrons to fill.
Draw all boxes for a subshell when you add the first electron to that subshell
Follow Aufbau Principle, Pauli Exclusion Principle and Hund’s Rule to fill in the electrons. 1s 2s 2p 3s 3p

32. What is the order for subshells?
You won’t have that energy and subshells chart on your test, so how did I know the order to draw and fill the subshells without looking back at that chart?
There are three possible ways, listed here in order of increasing preference:
Memorize it
Use a mnemonic device
Use the periodic table
We’ll cover these later.
For right now, just use the chart in your notes.

33. Example – Draw the orbital notation for sodium
Determine the number of electrons.
Since there is no charge indicated, the atom must be neutral.
# electrons = # protons = Atomic Number
Atomic number is 11, so…
there are 11 electrons to fill.
Draw all boxes for a subshell when you add the first electron to that subshell
Follow Aufbau Principle, Pauli Exclusion Principle and Hund’s Rule to fill in the electrons. 1s 2s 2p 3s

34. Example – Draw the orbital notation for manganese
Determine the number of electrons.
Since there is no charge indicated, the atom must be neutral.
# electrons = # protons = Atomic Number
Atomic number is 25, so…
there are 25 electrons to fill.
Draw all boxes for a subshell when you add the first electron to that subshell
Follow Aufbau Principle, Pauli Exclusion Principle and Hund’s Rule to fill in the electrons. 1s 2s 2p 3s 3p 4s 3d

35. Full Electron Configuration (Standard Notation)
Often just called “electron configuration,”
A much shorter way to show the arrangement of electrons in an atom compared to orbital notation.
Keeps the most important parts that determine the atom’s chemical properties, including how it will interact with light (and glow!).
Of the three rules, only the Aufbau Principle will apply to this notation.
Sometimes called spectroscopic notation.

36. Full Electron Configuration (Standard Notation)
Determine the number of electrons in the atom.
Follow the Aufbau Principle for filling the subhells in order.
The name of each subshell is written in order
ex 1s
Only the subshells that have electrons in them are written
The number of electrons is written as a superscript after the name of the subshell
Ex 1s2

37. Full Electron Configuration (Standard Notation)
How many electrons can each subshell hold?
Remember orbital notation?
The s subshell has 1 orbital, p has 3 orbitals, d has 5 orbitals and f has 7 orbitals
Remember each orbital can hold two electrons (one positive spin, one negative spin)?
So the maximum electrons it can hold depends on the type of subshell
s can hold 2
p can hold 6
d can hold 10
f can hold 14

38. Write the electron configuration for chlorine
Determine the number of electrons in the atom. 17
Follow the Aufbau Principle for filling the subhells in order.
The name of each subshell is written in order
The number of electrons is written as a superscript after the name of the subshell
1s22s22p
1s22s2
1s22s
1s22s22p6
1s22s22p63s 1s
1s22s22p63s23p
1s22s22p63s23p5
1s22s22p63s2
1s2

39. Write the electron configuration for aluminum
Determine the number of electrons in the atom. 13
Follow the Aufbau Principle for filling the subhells in order.
The name of each subshell is written in order
The number of electrons is written as a superscript after the name of the subshell
1s22s22p63s23p1

40. Write the electron configuration for zinc
Determine the number of electrons in the atom. 30
Follow the Aufbau Principle for filling the subhells in order.
The name of each subshell is written in order
The number of electrons is written as a superscript after the name of the subshell
1s22s22p63s23p64s23d10

41. Write the electron configuration for cesium
Determine the number of electrons in the atom. 55
Follow the Aufbau Principle for filling the subhells in order.
The name of each subshell is written in order
The number of electrons is written as a superscript after the name of the subshell
1s22s22p63s23p64s23d104p65s24d105p66s1

42. Noble Gas Configuration
Also called shorthand configuration
Since we follow the same pattern every time, all electron configurations look just like a noble gas plus a few extra electrons
Exceptions: hydrogen and helium
Cannot be used for elements in the 1st period (the two exceptions above)
Generally not used for elements in the 2nd period (it can be used, but it doesn’t really save any writing, so it usually isn’t)

43. Noble Gas Configuration
Why use noble gases?
Noble gases are stable – they have a full valence (outermost) shell of electrons (usually 8)
Noble gases are at the far right of the periodic table, so they are easy to find.

44. Noble Gas Configuration
Determine the number of electrons in the atom
Determine the noble gas to use
Use the noble gas in the previous period
Example – chlorine is in period 3. Neon is the noble gas in period 2 – use Neon
Warning: you can’t use a noble gas if it has the same number of electrons you are filling in either, so for argon you must use neon (which is the noble gas in the previous period)
Use the Aufbau Principle to fill in the remaining electrons

45. Write the noble gas configuration for chlorine
Determine the number of electrons in the atom 17
Determine the noble gas to use
Use the noble gas in the previous period
Use the Aufbau Principle to fill in the remaining electrons
Don’t forget – we’ve already accounted for all the electrons before 3s
[Ne]3s23p
[Ne]3s23p5
[Ne]3s
[Ne]3s2
[Ne]

46. Using the periodic table
The noble gas is written in square brackets
The next subshell is always an s subshell
The principal energy level (the number in front of the s) is always the period number that the element is in.
Chlorine is in the 3rd period, so after [Ne] we wrote 3s

47. Write the noble gas configuration for potassium
Determine the number of electrons in the atom 19
Determine the noble gas to use
Use the noble gas in the previous period
Use the Aufbau Principle to fill in the remaining electrons
Don’t forget – we’ve start with the s subshell with the principal energy level equal to the period number for potassium
[Ar]4s1

48. Write the noble gas configuration for arsenic
Determine the number of electrons in the atom 33
Determine the noble gas to use
Use the noble gas in the previous period
Use the Aufbau Principle to fill in the remaining electrons
Don’t forget – we’ve start with the s subshell with the principal energy level equal to the period number for arsenic
[Ar]4s23d104p3

49. Write the noble gas configuration for antimony
Determine the number of electrons in the atom 51
Determine the noble gas to use
Use the noble gas in the previous period
Use the Aufbau Principle to fill in the remaining electrons
Don’t forget – we’ve start with the s subshell with the principal energy level equal to the period number for antimony
[Kr]5s24d105p3

50. Write the noble gas configuration for bismuth
Determine the number of electrons in the atom 83
Determine the noble gas to use
Use the noble gas in the previous period
Use the Aufbau Principle to fill in the remaining electrons
Don’t forget – we’ve start with the s subshell with the principal energy level equal to the period number for antimony
[Xe]6s24f145d106p3

51. Periodic Table and Electron Configurations
How does the periodic table relate to electron configurations?
The periodic table has its “funny shape” because it is arranged based on electron configurations.
There are 4 distinct areas on the periodic table
2 groups on the far left
6 groups on the far right
10 groups in the middle (the transition metals!)
14 groups moved to the bottom (the inner transition metals)

52. Periodic Table and Electron Configurations
What is the highest energy subshell that has electrons for each of the alkali metals?
Write the noble gas configuration for each
Lithium [He] 2s1
Sodium [Ne] 3s1
Potassium [Ar] 4s1
Rubidium [Kr] 5s1
Cesium [Xe] 6s1
Francium [Rn] 7s1
They all have one electron in an s subshell
For group 2 they all have 2 electrons in an s subshell
Groups 1 and 2 are called the “s block” on the periodic table
Any s subshell can hold a maximum of 2 electrons… the “s block” is two groups wide!

53. Periodic Table and Electron Configurations
Look back at the noble gas configuration examples you did for arsenic, antimony and bismuth
They all have 3 electrons in a p subshell
How many electrons do you think nitrogen has in the 2p subshell?
How many electrons do you think phosphorous has in the 3p subshell?
Groups 13 through 18 are known as the “p block” since the subshell with the highest energy is a p subshell for each of those elements
Exception: helium
Any p subshell can hold a maximum of 6 electrons… the “p block” is six groups wide!

54. Periodic Table and Electron Configurations
The transition metals consist of 10 groups…
Which subshell has a maximum of 10 electrons?
The 10 groups of the transition metals, groups 2 through 12 are known as the d block
The inner transition metals are 14 across
An f subshell can hold up to 14 electrons
The inner transition metals are known as the f block

55. Electron configurations and the periodic table
Don’t forget helium!!!
s block
p block
d block
f block

56. What is the order for subshells?
Now lets figure out how to remember the proper order to fill the subshells in an atom
There are three possible ways, listed here in order of increasing preference:
Memorize it
Use a mnemonic device
Use the periodic table
We’ll cover these in reverse order, starting with Use the periodic table.

57. Electron configurations and the periodic table What is the order for subshells?
No matter which method you use to remember the order of the subshells, there are some important facts:
Remember that the lowest energy p subshell is 2p (1p doesn’t exist)
The lowest d subshell is 3d
The lowest f subshell is 4f
So we can label our periodic tables to help us with electron configurations (method 3 – Use the periodic table)

58. Electron configurations and the periodic table
Don’t forget helium!!!
s block
p block
d block 1s 1s 2s 3s 4s 5s 6s 7s 1s 2p 3p 4p 5p 6p 3d 4d 5d 6d 4f 5f
f block

59. Electron configurations and the periodic table What is the order for subshells?
If you label your periodic table this way, you can simply follow the periodic table to figure out what order to fill sublevels for the Aufbau Principle.
Start with hydrogen and keep adding sublevels until you run out of electrons!

60. What is the order for subshells?
Method 2 – use a mnemonic device.
The problem with this, is that you still have to remember how to make the mnemonic device, as well as how to use it.
I don’t like this very much, but its better than Method 1 “memorize it”

61. Mnemonic Device 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d
Construct a grid – it helps if your boxes are perfectly square
In the first column, start with 1s and end with 6s
In the second column, start with 2p (remember 1p doesn’t exist!) and end with 6p.
Be sure that 2p is in the same ROW as 2s
3d to 6d goes in the 3rd column
4f and 5f go in the last column
Mnemonic Device 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d

62. Mnemonic Device 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d
Now draw diagonal arrows starting in the upper right corner of the top box in the first column
Continue drawing arrows for each box across the top row… extend the arrows through to the far left of the grid
Now move down the right column until you run out of boxes
To help you remember what order to follow the arrows you may want to number them (in the order that we drew them)
Mnemonic Device 1 2 3 4 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 5 6 7 8

63. Mnemonic Device 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 1s
To correctly order the subshells, simply follow the arrows.
And so on
Mnemonic Device 1 2 3 4 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 1s 2s 2p 3s 3p 4s 3d 4p 5s 5 6 7 8