Electron Configuration
Mapping the electrons
Electron Configuration

The way electrons are arranged
around the nucleus.
Quantum Mechanical Model
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1920’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 Schrodinger
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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.
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
Energy Sublevels
s
p
d
f
g
Orbitals

The principle quantum number, n,
determines the number of sublevels
within the principle energy level.
Orbital Quantum Number, ℓ
(Angular Momentum Quantum Number)

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Indicates shape of orbital sublevels
ℓ = n-1
ℓ
sublevel
0
1
2
3
4
s
p
d
f
g
Orbital

The space where there is a high
probability that it is occupied by a pair
of electrons.
Visualizing the orbitals
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
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Standard
Shorthand
Orbital
Diagram
for Fluorine
Blocks in the Periodic Table
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