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Electron Configuration
Mapping the electrons
Electron Configuration

The way electrons are arranged
around the nucleus.
Quantum Mechanical Model

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1920’s-1930’s
Werner Heisenberg (Uncertainty Principle)
Louis de Broglie (electron has wave
properties)
Erwin Schrodinger (mathematical equations
using probability, quantum numbers)
Heisenberg uncertainty
principle

it is impossible to
determine simultaneously both the
position and velocity of an electron or
any other particle with any great degree
of accuracy or certainty.
Erwin Schroedinger

Formulated equation that describes
behavior and energies of subatomic
particles.

Incorporates both particle and wave
behavior in terms of wave function:
is proportional to the probability of
finding an electron.
Erwin Schroedinger (cont’d)

Leads to Quantum Mechanics: we
cannot pinpoint an electron in an atom
but we can define the region where
electrons can be in a particular
time……. called a “probability map”….a
3-dimensional area in space called an
ORBITAL
Principal Quantum Number, n

Indicates main energy levels
n = 1, 2, 3, 4…

Each main energy level has sub-levels
s
p
d
f
Orbital Quantum Number, ℓ
(Angular Momentum Quantum Number)


Indicates shape of orbital sublevels
ℓ = n-1
ℓ
sublevel
0
1
2
3
4
s
p
d
f
g
Quantum numbers and orbital energies
Each electron in an atom has a unique set of quantum
numbers to define it
{ n, l, ml, ms }

n = principal quantum number

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l = azimuthal quantum number


for orbitals of same n, l distinguishes different shapes
(angular momentum)
ml = magnetic quantum number


electron’s energy depends principally on this
for orbitals of same n & l, ml distinguishes different
orientations in space
ms = spin quantum number

for orbitals of same n, l & ml, ms identifies the two
possible spin orientations

Energy level
n=1
Sublevel
1s (l = 0)
# of orbitals/sublevel
1 (ml has one value)

n=2
2s (l = 0)
2p (l = 1)
1 (ml has one value)
3 (ml has three values)

n=3
3s (l = 0)
3p (l = 1)
3d (l = 2)
1 (ml has one value)
3 (ml has three values)
5 (ml has five values)

n = principal
quantum
number
(energy)
l = azimuthal
quantum
number
(shape)
ml =
magnetic
quantum
number
(orientation)
Concept: Each electron in an atom has a unique set of quantum numbers to
define it
{ n, l, ml, ms }
11

The principle quantum number, n,
determines the number of sublevels
within the principle energy level.
Orbital


The space where there is a high
probability that it is occupied by a pair
of electrons.
Orbitals are solutions of Schrodinger’s
equations.
Orbitals
Visualizing the orbitals



s orbitals are
spherical
p orbitals are
“dumbell” shaped
d and f are harder
to visualize
Orbitals in Sublevels
Sublevel
s
p
d
f
# Orbitals
1
3
5
7
# electrons
2
6
10
14
Three rules are used to build
the electron configuration:
Aufbau principle
 Pauli Exclusion Principle
 Hund’s Rule

Aufbau Principle

Electrons occupy orbitals of lower
energy first.
Orbital
Diagram
Filling Order diagram
-Pauli Exclusion Principle
(Wolfgang Pauli, Austria, 1900-1958)
-Electron Spin Quantum Number


An orbital can hold only two electrons and
they must have opposite spin.
Electron Spin Quantum Number (ms):
+1/2, -1/2
Hund’s Rule
In a set of orbitals, the electrons will fill the
orbitals in a way that would give the
maximum number of parallel spins
(maximum number of unpaired electrons).
Analogy: Students could fill each seat of a
school bus, one person at a time, before
doubling up.
Orbital
Diagram for
Hydrogen
Orbital
Diagram
for Helium
Orbital
Diagram
for Lithium
Orbital
Diagram
for
Beryllium
Orbital
Diagram
for Boron
Orbital
Diagram
for Carbon
Orbital
Diagram
for
Nitrogen
Orbital
Diagram
Notations of Electron
Configurations


Standard
Shorthand
Orbital
Diagram
for Fluorine
Standard Notation
of Fluorine
2
1s
Number of electrons
in the sub level 2,2,5
2
2s
5
2p
Sublevels
Shorthand Notation

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Use the last noble gas that is located in
the periodic table right before the
element.
Write the symbol of the noble gas in
brackets.
Write the remaining configuration after
the brackets.
Ex: Fluorine: [He] 2s2 2p5
Blocks in the Periodic Table