ELECTRON
CONFIGURATION
THE QUANTUM MECHANICAL MODEL



The e- is found inside a
blurry “electron cloud”
An area where there is
a chance of finding an
electron.
Only found with 90%
accuracy in the area
WHERE CAN WE FIND ELECTRONS?

Each element has its own e- configuration for
its ground state
 No

charges
We base them on where the LAST e- is
placed
IT’S LIKE AN ADDRESS…
State – city – street – house #
 State is called the Principle Energy level
 City is called the sublevel
 Street is called the orbital
 House # is the e- spin direction

PRINCIPLE ENERGY LEVELS
We have 1-7
 Highest occupied ground state energy level =
PT period #
 Main energy levels Bohr found

SUBLEVELS

Each energy level has increasing number of
sublevels
 Level
1 has 1 sublevel
 Level 2 has 2 sublevels
 Level 3 has 3 sublevels
 And so on….

Though 7 major levels…only 4 main
sublevels are needed to describe existing
atoms
SUBLEVEL
Sublevels are distinguished by the shape of
orbitals in them
 There are currently four of them
s
p
d
f

ORBITALS
In each sublevel there are specific orbitals
 An Orbital is a 3-D region in space an e- can
be found

 Does
not have “hard and fast” boundaries
 See
next slide
Each orbital can hold only 2 e Mathematically found through wave function

WHAT’S GOING ON…
S - SUBLEVEL
1 orbital in this sublevel
 Sphere shape
 Total 2 e- possible
 Same shape in each
level…just bigger
 Found in ALL energy
levels

p - SUBLEVEL
3 orbitals in this sublevel
 Dumbbell shaped
 Total 6 e Found in Energy Level 2 or Higher
 Node between each half of each orbital

 Intermediate
area between high probability areas
d - SUBLEVEL
5 orbitals in this sublevel
 Clover shape
 Total 10 possible e Found in Energy Level 3 or higher.

f - SUBLEVEL
7 orbitals in this sublevel
 Total 14 e- possible
 Complex shape
 Found in Energy Level 4 or higher

ENERGY - SUBLEVEL
Sublevels
1
2
s
s, p
3
4
5
s, p, d
s, p, d, f
s, p, d, f, g
6
7
s, p, d, f, g, h
s, p, d, f, g, h, i
We will only commonly use s, p, d, and f!!
HOW WE WRITE WHERE E- ARE
State – city – street – house #
 State is called the principle E level
 City is called the sublevel
 Street is called the orbital
 House # is the e- spin direction

5
32 e18 e8 e2 e-
4
3
2
1
f
d
p
s
nucleus
Increasing energy
7s
6s
5s
7p
6p
5p
4p
4s
3p
3s
2p
2s
1s
6d
5d
4d
3d
5f
4f
7s
6s
5s
7p
6p
6d
5f
5d
5p
4f
4d
4p
3d
4s
3p
3s
2p
2s
1s
1s
2
=
1s
ELECTRON CONFIGURATION RULES
 The

way electrons are arranged in atoms.
Aufbau principle- electrons enter the
lowest energy first.
 Must
fully fill before move to next
 This causes difficulties because of the
overlap of orbitals of different energies.
RULES CONTINUED

Pauli Exclusion Principle- no 2 e- can have
same set of 4 quantum #
 at

most 2 electrons per orbital - different spins!!
Hund’s Rule- “up, up, up before down,
down, down”
 All
orbitals need to be filled w/one “up” spin
(positive--clockwise) before any in the sublevel is
filled with a “down” spin (negative-counterclockwise)
DRAWING ORBITAL NOTATION
 A box is used to represent each orbital.
 Arrows are used to represent each electron.
**remember opposite spins.
Example: the orbital notation for carbon is:
1s
2s
2p
ORBITAL NOTATION
Lets try a few:
 Orbital Notation for O

O
= 8 e1s

2s
2p
Orbital Notation for Cl
 Cl
1s
= 17e-
2s
2p
3s
3p
Electron Configuration
# of electrons
1s
Principle
Energy Level
2
sublevel
Interpret the following
Electron Configuration
4 electrons
4
3p
3rd Energy Level
p sublevel
WHEN DOING A CONFIGURATION…
Use the total number of e Slowly place e- in order till run out of e Example

B
5e-
2 in 1s2…3 left over
 Next 2 can go is 2s2 …1 left over
 Last one goes in 2p, but since only 1 left it is 2p1
 Final configuration
1s2 2s2 2p1
 First
TRY A FEW
K
 Cl
 Fe
 Pb

ANSWERS

K
 1s2 2s2 2p6 3s2 3p6 4s1

Cl
 1s2 2s2 2p6 3s2 3p5

Fe
 1s2 2s2 2p6 3s2 3p6 4s2 3d6

Pb
 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6
6s2 5d10 6p2
5s2 4d10 5p6
TONIGHT’S HOMEWORK

Write out the e- configuration for elements
Hydrogen through and including Yttrium
DO NOW:

Box all things written with the HIGHEST
PRINCIPLE energy level for each configuration
of your homework
 Ex:

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3
Circle the LAST THING WRITTEN for each
configuration of your homework
 Ex:
1s2 2s2 2p6 3s2 3p6 4s2 3d6
OUTERLEVEL (SHELL) CONFIGURATION

Everything is the outside/highest PRINCPLE
ENERGY LEVEL
 Max
is 8 e- total
 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3
EXAMPLES
Ga
 Ra
 Mn
 Se
 Am
 Br

EXAMPLES
Ga- 4s24p1
 Ra- 7s2
 Mn- 4s2
 Se- 4s24p4
 Am- 7s2
 Br- 4s24p5

SUBLEVEL (SHELL) CONFIGURATION

The last thing written for the e- configuration
 1s2 2s2 2p6 3s2 3p6 4s2 3d6
 Every
element has its own ground level subshell
configuration unique to itself
EXAMPLES
F
 Ca
 Al
 Pa
 Mo
 Xe

EXAMPLES
F- 2p5
 Ca- 4s2
 Al- 3p1
 Pa- 5f3
 Mo- 4d4
 Xe- 5p6

NOBLE GAS CONFIGURATIONS

In order to save time and your hand when
writing out electron configurations, one may
use the Noble Gas Notation.
A
noble gas symbol is used in place of a long list of
electron configurations.
 Example: Ar: 1s2 2s2 2p6 3s2 3p6 = [Ar]
 Noble Gas Shorthand Configuration for Ca
 Ca:
[Ar] 4s2
EXAMPLES – NOBLE GAS CONFIGURATIONS

Sr

W

Hg

Cl
CHARGED ATOMS

Can do e- configurations for ions, but must
make sure to note that that is what you are
doing!
 Same
way, just use the number of e- in the ion
involved