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ORBITAL NOTATION 9/06
SHELL (energy level, principle quantum number)
– probability cloud location of electrons.
SUBLEVEL – a division of a shell, s, p, d, f
ORBITAL (not orbit) a pair of electrons with
opposite spin.
1. s sublevel – one orbital, MAX 2
electrons.In all shells.
2. p sublevel- three orbitals, MAX 6
electrons. Shell 2 and higher.
3. d sublevel- five orbitals, MAX 10
electrons. Shell 3 and higher.
Electrons MUST fill inner sublevels first
(ground state). This is called the Aufbau
process as demonstrated below.
Electrons in the same orbital MUST have
opposite magnetic spin (Pauli Exculsion
Principle).
To fill “p sublevels” you add one electron to
each, then go back and add the second until you
have assigned all electrons, this is called
Hund’s rule and is demonstrated below.
FILLING ORDER FOR FIRST TWO SHELLS.
1s ↑↓
2s↑↓
2p ↑↓ ↑↓ ↑↓
EXAMPLE ONE – PREDICT THE GROUND STATE OF CARBON.
1. Look up the atomic number (PERIODIC TABLE),
this will equal the number of electrons in the
ground state (however, not in the ionic state)
2. Look at the notation for electrons under the
atomic number.
3. Begin filling the 1s, then the 2s, then the 2p
until you have assigned all electrons.
1- 6C carbon has an atomic number of 6,
therefore you must assign 6 electrons for the
ground state.
2- Under the atomic number you should see the
numbers 2-4, which means there are 2 electrons in
the first shell and four in the second shell.
3- Apply the Aufbau process and Hunds rule.
1st electron:
1s ↑
2s
2p __ __ __
2nd electron:
1s ↑↓
2s
2p __ __ __
3rd electron:
1s ↑↓
2s↑
2p __ __ __
4th electron:
1s ↑↓
2s↑↓
2p __ __ __
5th electron:
1s ↑↓
2s↑↓
2p ↑_ __ __
6th electron:
1s ↑↓
2s↑↓
2p ↑
↑
__
 at this point you have assigned all electrons
and are finished, the configuration is
1s2
2s2 2p4
NOTE the superscripts are NOT
exponents, they indicate how many electrons are in a
sublevel.
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EXAMPLE TWO – PREDICT THE GROUND STATE OF OXYGEN.
1. Look up the atomic number (PERIODIC TABLE),
this will equal the number of electrons in the
ground state (however, not in the ionic state)
2. Look at the notation for electrons under the
atomic number.
3. Begin filling the 1s, then the 2s, then the 2p
until you have assigned all electrons.
1- 8O carbon has an atomic number of 8,
therefore you must assign 6 electrons for the
ground state.
2- Under the atomic number you should see the
numbers 2-6, which means there are 2 electros in
the first shell and six in shell 2.
3- Apply the Aufbau process and Hunds rule.
1st electron:
1s ↑
2s
2p __ __ __
2nd electron:
1s ↑↓
2s
2p __ __ __
3rd electron:
1s ↑↓
2s↑
2p __ __ __
4th electron:
1s ↑↓
2s↑↓
2p __ __ __
5th electron:
1s ↑↓
2s↑↓
2p ↑_ __ __
6th electron:
1s ↑↓
2s↑↓
2p ↑
↑
__
7th electron:
1s ↑↓
2s↑↓
2p ↑
↑
↑
8th electron:
1s ↑↓
2s↑↓
2p ↑↓ ↑
↑
 at this point you have assigned all electrons
and are finished, the configuration is
1s2
2s2 2p4
NOTE the superscripts are NOT
exponents, they indicate how many electrons are in a
sublevel.