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


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 f d s p g

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

Orbitals in Sublevels
Sublevel # Orbitals # electrons f d s p g
1
3
5
7
9
2
6
10
14
18

Three rules are used to build the electron configuration:
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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 (m s
):
+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
Number of electrons in the sub level 2,2,5
1 s 2 2 s 2 2 p 5
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] 2 s 2 2 p 5

Blocks in the Periodic Table