Orbital Diagrams and
Electron Configurations
Vocabulary:
1. Electron
configuration
2. Aufbau Principle
3. Pauli Exclusion
Principle
4. electron spin
5. Hund’s Rule
6. Orbital diagram
Paul Klee, Greeting, 1922. American.
Subshells
• We’ve talked about the different orbitals
(subshells) that give us the probable location of
electrons of various energy states. But how do
we know which subshell any one electron will
occupy? Should it go in an s, p, d, or f orbital?
And which energy level?
• Luckily there are 3 rules to guide our
understanding of the position of ground state
electrons in an atom.
The rules:
1. The Aufbau Principle:
Electrons fill orbitals with
the lowest energy first.
“Aufbau” is German
for “Building up.”
The rules:
To follow the Aufbau principle, you must know the
order of orbital energy. The following chart will
help you with this order:
1st Energy level
1s
There is only an s
orbital on the 1st
energy level.
The rules:
To follow the Aufbau principle, you must know the
order of orbital energy. The following chart will
help you with this order:
1st Energy level
2nd Energy level
1s
2s 2p
There are only s and p
orbitals on the 2nd
energy level.
The rules:
To follow the Aufbau principle, you must know the
order of orbital energy. The following chart will
help you with this order:
1st Energy level
2nd Energy level
3rd Energy level
1s
2s 2p
3s 3p 3d
There are only s, p,
and d orbitals on the
3rd energy level.
The rules:
To follow the Aufbau principle, you must know the
order of orbital energy. The following chart will
help you with this order:
1st Energy level
2nd Energy level
3rd Energy level
4th Energy level
5th Energy level
6th Energy level
7th Energy level
1s
2s
3s
4s
5s
6s
7s
2p
3p
4p
5p
6p
7p
3d
4d 4f
5d 5f
6d 6f
7d 7f
The 4th, 5th, 6th, and
7th energy levels
contain all 4 types of
orbitals (although you
will not ever use the
6f , 7d, or 7f orbitals.)
The rules:
Sadly, the order of increasing energy does not follow
left to right, top to bottom on this chart. Instead you
need to add some arrows to help with the order.
Start here
1st Energy level
2nd Energy level
3rd Energy level
4th Energy level
5th Energy level
6th Energy level
7th Energy level
1s
2s
3s
4s
5s
6s
7s
2p
3p
4p
5p
6p
7p
3d
4d 4f
5d 5f
6d 6f
7d 7f
The rules
• So following the chart, the order of the
orbitals in increasing energy is:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s,
4f, 5d, 6p, 7s, 5f, 6d, and 7p.
The rules
2. The Pauli
Exclusion Principle:
Only two electrons can
occupy each orbital, but
each must have
opposite spin.
Wolfgang Pauli
(Austria):
Nobel prize in
Physics, 1945
The rules
•Spin refers to a magnetic field created by an
electron. Two electrons in the same orbital must
have opposite spin meaning they have opposite
magnetic field orientation.
•We’ll represent this using an up arrow for an
electron with + spin and a down arrow for an
electron with – spin.
 = electron with positive spin
 = electron with negative spin
The rules
3. Hund’s Rule: If two or more
orbitals of equal energy are
available, electrons will occupy
them singly before filling them in
pairs.
Friedrich
Hund
(German)
The rules
So for example, if you are placing 4 electrons
into the 2p orbitals, they would fill in the
following order due to Hund’s Rule:
correct
2p __ __ __
incorrect
2p __ __ __
So let’s see the rules in action!
• Draw the orbital diagram for carbon (6 electrons).
Rule 1: Use chart to fill lowest energy orbitals first.
Rule 2: Two electrons in each orbital with opposite spin.
Rule 3: Fill orbitals of equal energy 1 at a time and then pair up.
1s ___
2s ___
2p ___ ___ ___
3 lines because there are 3 types of p-orbitals.
So let’s see the rules in action!
• Draw the orbital diagram for carbon (6 electrons).
Rule 1: Use chart to fill lowest energy orbitals first.
Rule 2: Two electrons in each orbital with opposite spin.
Rule 3: Fill orbitals of equal energy 1 at a time and then pair up.
1s ___
2s ___
2p ___ ___ ___
The six arrows represent the positions of the six
electrons in a ground state carbon atom.
So let’s see the rules in action!
• Draw the orbital diagram for carbon (6 electrons).
Rule 1: Use chart to fill lowest energy orbitals first.
Rule 2: Two electrons in each orbital with opposite spin.
Rule 3: Fill orbitals of equal energy 1 at a time and then pair up.
1s ___
2s ___
2p ___ ___ ___
We can show this orbital diagram in a more
abbreviated form called an electron
configuration.
So let’s see the rules in action!
• Draw the orbital diagram for carbon (6 electrons).
Rule 1: Use chart to fill lowest energy orbitals first.
Rule 2: Two electrons in each orbital with opposite spin.
Rule 3: Fill orbitals of equal energy 1 at a time and then pair up.
1s ___
2s ___
2p ___ ___ ___
1s2 2s2 2p2
This is the electron
configuration for
carbon.
Let’s try another one.
• Draw the orbital diagram and write the electron
configuration for iron: 26 electrons.
1s __
2s __ 2p __ __ __
3s __ 3p __ __ __ 3d __ __ __ __ __
4s __ 4p __ __ __ 4d __ __ __ __ __
Electron Configuration:
1s22s22p63s23p64s23d6
Try one on your own.
• Draw the orbital diagram and write the electron
configuration for rubidium: 37 electrons.
Try one on your own.
• Draw the orbital diagram and write the electron
configuration for rubidium: 37 electrons.
1s __
2s __ 2p __ __ __
3s __ 3p __ __ __ 3d __ __ __ __ __
4s __ 4p __ __ __ 4d __ __ __ __ __
5s __
Electron Configuration:
1s22s22p63s23p64s23d104p65s1