ELECTRON
CONFIGURATION
By Hilary Scurlock
Edited by Mrs. Rosenfield
Electron Configurations
• Describe the location of electrons
• Orbital = region of space (same as electron
cloud)
• Principle quantum # (n) = energy level
– n = 1, 2, 3, 4, 5 …
with increasing distance from the nucleus
• Energy Sublevels = s, p, d, f (see p. 133-134)
–s
sphere
1 orbital
max 2 electrons
–p
dumbbell 3 (x, y, z)
6
–d
clover leaf 5
10
–f
7
14
• Max 2 electrons in each orbital
Atomic Orbitals
http://winter.group.shef.ac.uk/orbitron/AOs/1s/index.html
This site shows 3-D versions of the atomic orbitals – I just thought you
would be interested
Some important info…
• There are 4 quantum numbers that are
associated with electron configurations:
– Principal quantum number (n) = energy level
– Angular momentum quantum number (l ) =
sublevel, which is the type of orbitals (s, p, d,
or f)
– Azmuthal quantum number (m l ) = number of
orbitals related to the sublevel
– Electron spin quantum number (ms) = tells if
electrons are spinning clockwise or counter
clockwise
• We can use the four quantum numbers to
label each unique electron in any orbital in
any atom, thus giving us electron
configuration.
• The quantum numbers are just like your
address!
• No two electrons will have the same four
quantum numbers
Principal quantum number (n)
• n can be any integer from 1 to infinity
• It tells you the energy level
• The larger the number the higher the
energy level
Angular momentum quantum
number (l )
•l
is any integer from
0 to n – 1
• It tells you the type of
sublevel
l
0
Sublevel
Type
sS
1
pP
2
dD
3
fF
value
Azmuthal quantum number (m l )
• Tells you the number of orbitals related to
the sublevel
• m l is any integer from – l to + l
Electron spin quantum number (ms)
• This tells if electrons are spinning
clockwise or counter clockwise
• ms is either + ½ or – ½
• For all electron configurations you will not
know if the electrons are clockwise or
counter clockwise but with orbital notation
you will.
For example
the electron configuration for Hydrogen is:
1s1
# of electrons in orbital or subshell
Principal
quantum # (n)
Angular momentum
quantum # (l)
NOTICE:
For electron configurations ml and ms are not used
Orbital Diagrams
• These show us the number of orbitals and
the spin of the electrons in those orbitals.
– Here ml and ms are used
This box represents
the orbital number
(ml)
H
1s1
The arrow denotes
one of the two
possible spinning
motions (ms)
It can also be given
as lines or circles
Knowing this, now we can draw out a
configuration and an orbital notation
• Helium
– 2 electrons
• Beryllium
– 4 electrons
• Lithium
– 3 electrons
• Helium
1s2
___
1s2
• Beryllium 1s22s2
___ ___
1s2 2s2
•
Lithium
1s22s1
___ ___
1s2 2s1
An Electron configuration is how the electrons are
distributed among the various atomic orbitals.
Some Rules to Configure By:
If you want to get these electron configurations/orbital
diagrams right there are some rules that we must follow.
PAULI EXCLUSION PRINCIPLE
• This principle states that two electrons in
the same orbital must have opposite spins.
• An example of the Pauli exclusion
principle:
• He (1s2): ____
____
1s2
1s2
HUND’S RULE
• Electrons entering a subshell containing more
than one orbital (Ex: p, d or f - orbitals) will be
the most stable if the electrons are arranged by
themselves in separate orbitals alone before
being paired up.
• An example of Hund’s rule:
• Nitrogen (1s2 2s2 2p3):
___ ___ ___ ___ ___
1s2
2s2
2p3
• What would fluorine look like?
AUFBAU PRINCIPLE
• Electrons start at the lowest energy orbitals first and then
continue to fill orbitals of increasing energy.
• How do we know the order????
Order of filling orbitals (p.135)
Those wacky d orbitals!
• When dealing with transition metals, which
have d orbitals, always fill the s-orbital in
the next energy level before filling the dorbital.
• For example, the configurations of
elements such as Sc are different than we
might expect, because, in the cases of this
element, the 4s orbital is filled before the
3d orbital.
• 1s2 2s2 2p6 3s2 3p6 4s2 3d1
• The electrons follow a
general pattern when
filling energy levels and
orbitals and guess what
object we can thank in
helping us figure this
out????
• THE PERIODIC TABLE
Review of Writing Electron
Configurations
Ask yourself these questions every time you have to
write an electron configuration or orbital notation:
1. Where is the element on the periodic table?
2. What is the atomic number?
3. How many electrons?
4. What is the row number?
5. How many energy levels?
6. What subshell(s) does the element have?
7. What is the electron configuration?
ONLY CONTINUE IF YOU HAVE TO WRITE ORBITAL
NOTATIONS:
8. How many orbitals in each subshell?
9. What is the orbital notation?
Some Examples:
• Give the electron configuration for the
following:
He
O
Ar
Be
Na
Te
• Give the orbital diagram for the following:
Li
C
V
K
Quick Quiz!
• What is wrong with
this configuration?
Al: 1s22s22p43s23p3
Where do the Lanthanide’s and
Actinide’s fit in???
• Lanthanides (f-block) Ce-Lu
• Actinides (f-block) Th-Lr
• Ce
1s22s22p63s23p64s23d104p65s24d105p66s24f15d1
• Cm
1s22s22p63s23p64s23d104p65s24d105p66s24f145d10
7s26d15f7
• Hg
1s22s22p63s23p64s23d104p65s24d105p66s24f145d10
A SHORTCUT 
• You do not have to write out all the info
Noble gas core
• Li = [He] 2s1
• P = [Ne] 3s23p3
• TRY
Oxygen
Zinc
Cesium
Exceptions to the Rules
• Just as with any good rule there are
exceptions!!!
• An atom with almost half or completely filled d and f orbitals are more stable when
you can fill them from an s-orbital
• Ex: Chromium = [Ar]4s13d5 OR
Copper = [Ar]4s13d10
• You try:
– Molybdenum = Mo
– Gold = Au
– Europium = Eu
Valence Electrons
• These electrons determine the chemical properties of an
element
• They are generally the electrons in the atom’s highest
energy levels.
– Determine the number of valence electrons using electron
configurations:
– S
[Ne] 3s2 3p4
= 6 valence e– Cs
[Xe] 6s1
= 1 valence e– Fe
[Ar] 4s2 3d6
= 2 valence e– Br
[Ar] 4s2 3d10 4p5 = 7 valence e-
• On the periodic table elements in the same column tend
to have the same number of valence electrons.
Electron-dot Structures
• Visual way to show valence electrons of
an element for bonding.
• Has element’s symbol in the middle and is
surrounded by dots representing the
atom’s valence electrons.
– Dots are placed one at a time on the four
sides of the symbol and then paired up until
they are all used.
Examples of Electron-dot
Structures
S
Cs
Fe
Br
See pg 140 – 141 for
more examples
DIAMAGNETISM and
PARAMAGNETISM
• Paramagnetic substances
are those that are
attracted by a magnet.
Because the electrons
have parallel spins, the
magnetic fields reinforce
each other.
• Diamagnetic substances
always repel magnets.
Because the electrons
have antiparallel spins,
the two magnetic fields
cancel each other out.
N
N
S
N
N
S
S
N
S
S
DIAMAGNETIC
PARAMAGNETIC
Electron Configurations of Ions
(“Noble” Configurations)
• So where do the electrons of ions add and
leave from?
• Octet Rule is the key
•
•
•
•
Examples:
N3Na+
Zn2+