Section 4.3—Electron
Structure
The Electron Hotel
The story of the Electron Hotel
Shopping Center
Parking Garage
Restaurant
A man built an 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.
How the Electron Hotel Fills
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 (actually it was the fire inspector
that insisted on this one)
• 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 8 people come to the hotel, where would he put them?
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 (actually it was the fire inspector
that insisted on this one)
• 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?
You Try
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 (actually it was the fire inspector
that insisted on this one)
• 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 42 people come to the hotel, where would he put them?
Where do electrons really live?
Electron Clouds
They don’t live in a hotel…They are in
the area outside of the nucleus where
the electrons reside.
Electron Clouds
Electron Hotel
Electron
cloud
Which section
of the hotel
Principal
energy levels
The electron cloud is
made of energy levels
Which floor
Subshells
Energy levels are
composed of subshells
Which room
Orbitals
Subshells have orbitals.
Subshell versus Orbital
Subshell – A set of orbitals with equal
energy
Orbital – Area of high probability of the
electron being located.
Each orbital can hold 2 electrons
Energy increases
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
d
3
5
10
f
4
7
14
Electron Configuration
What are electron configurations?
They show the grouping and position of
electrons in an atom.
The number and configuration of electrons
determines how something glows…so it’s
important to know “where the electrons live” for
an atom!
Electron configurations use boxes for orbitals and
arrows for electrons.
Energy and Subshells
6p
6s
5p
5d
4f
4d
5s
4p
3d
4s
3p
3s
2p
Energy
2s
Subshells are filled from
the lowest energy level to
increasing energy levels.
Does this look familiar? Electron Hotel!
1s
Aufbau Principle
The first of 3 rules that govern electron configurations
1
Aufbau Principle: Electrons fill subshells (and
orbitals) so that the total energy of atom is the
minimum
What does this mean?
Electrons must fill the lowest available subshells and orbitals before
moving on to the next higher energy subshell/orbital.
Where did we see this “rule” in the Electron Hotel?
Hund’s Rule
2
Hund’s Rule: Place electrons in unoccupied
orbitals of the same energy level before doubling
up.
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?
Pauli Exclusion Principle
3
Pauli Exclusion Principle: Two electrons that
occupy the same orbital must have different spins.
“Spin” describes the angular
momentum of the electron
How does this work?
“Spin” is designated with an up
or down arrow.
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?
Determining the Number of Electrons
Charge = # of protons – # of electrons
Atomic number = # of protons
Example:
How many
electrons
does Br-1
have?
Determining the Number of Electrons
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
Writing Electron Configurations
1
Aufbau Principle: Electrons fill subshells (and orbitals) so that
the total energy of atom is the minimum
2
Hund’s Rule: Place electrons in unoccupied orbitals of the
same energy level before doubling up.
3
Pauli Exclusion Principle: Two electrons that occupy the same
orbital must have different spins.
Example:
Write the
boxes &
arrows
configuration
for Cl
Writing Electron Configurations
1
Aufbau Principle: Electrons fill subshells (and orbitals) so that
the total energy of atom is the minimum
2
Hund’s Rule: Place electrons in unoccupied orbitals of the
same energy level before doubling up.
3
Pauli Exclusion Principle: Two electrons that occupy the same
orbital must have different spins.
Example:
Write the
boxes &
arrows
configuration
for Cl
1s
No charge written  Charge is 0
Atomic number for Cl = 17 = # of protons
0 = 17 - electrons
Electrons = 17
2s
2p
4
9
70
6
5
3
2
1
8
17
16
15
14
13
12
11
3s
3p
Spectroscopic Notation
Spectroscopic Notation
Shorthand way of showing electron
configurations
The number of electrons in a subshell are
shown as a superscript after the subshell
designation
1s
2s
2p
3s
1s2 2s2 2p6 3s2 3p5
3p
Writing Spectroscopic Notation
1
Determine the number of electrons to place
2
Follow Aufbau Principle for filling order
3
Fill in subshells until they reach their max (s = 2, p = 6, d = 10,
f = 14).
4
The total of all the superscripts is equal to the number of
electrons.
Example:
Write
spectroscopi
c notation for
S
No charge written  Charge is 0
Atomic number for S = 16 = # of protons
0 = 16 - electrons
1s 2 2s 2 2p 6 3s 2 3p 4
Electrons = 16
2 + 2 + 6 + 2 + 4 = 16
Noble Gas Configuration
Noble Gases & Noble Gas Notation
Noble Gas – Group 8 of the Periodic
Table. They contain full valence shells.
Noble Gas Notation – Noble gas is
used to represent the core (inner)
electrons and only the valence shell is
shown.
Br
Spectroscopic
Noble gas
1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 5
[Ar] 4s 2 3d 10 4p 5
The “[Ar]” represents the core electrons and only the valence electrons are shown
Which Noble Gas Do You Choose?
How do you know which noble gas to use to symbolize
the core electrons?
Think: Price is Right.
How do you win on the Price is Right?
By getting as close as possible without going over.
Choose the noble gas that’s closest without going over!
Noble Gas
# of electrons
He
2
Ne
10
Ar
18
Kr
36
Xe
54
Noble Gas Notation Example
1
Determine the number of electrons to place
2
Determine which noble gas to use
3
Start where the noble gas left off and write spectroscopic
notation for the valence electrons
Example:
Write noble
gas notation
for As
Noble Gas Notation Example
1
Determine the number of electrons to place
2
Determine which noble gas to use
3
Start where the noble gas left off and write spectroscopic
notation for the valence electrons
No charge written  Charge is 0
Atomic number for As = 33 = # of protons
Example:
Write noble
gas notation
for As
0 = 33 - electrons
[Ar] 4s 2 3d 10 4p 3
Electrons = 33
Closest noble gas: Ar (18)
Ar is full up through 3p
18 + 2 + 10 + 3 = 33