chemistry
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5.2
Electron Arrangement in
Atoms
>
Electron Configurations
The ways in which electrons are arranged in
various orbitals around the nuclei of atoms are
called electron configurations.
Three rules—the aufbau principle, the
Pauli exclusion principle, and Hund’s
rule—tell you how to find the electron
configurations of atoms.
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5.2
Electron Arrangement in
Atoms
>
Electron Configurations
Aufbau Principle
According to the aufbau principle, electrons
occupy the orbitals of lowest energy first. In the
aufbau diagram below, each box represents an
atomic orbital.
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5.2
Electron Arrangement in
Atoms
>
Electron Configurations
Pauli Exclusion Principle
According to the Pauli exclusion principle, no
two electrons in an atom can have the same four
quantum numbers.
What does that mean?
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Electron Arrangement in
Atoms
>
Quantum Numbers: like addresses for
electrons
•(n) size of cloud (all w same n are in same
energy level)
•(l) shape of cloud (depends on orbital)
•(m) orientation (depends on orbital)
•(s) spin (clockwise or counterclockwise)
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5.2
Electron Arrangement in
Atoms
>
Electron Configurations
Hund’s Rule
Hund’s rule states that electrons occupy orbitals
of the same energy in a way that makes the
number of electrons with the same spin direction
as large as possible.
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5.2
Electron Arrangement in
Atoms
>
Electron Configurations
Orbital Filling Diagram
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1s22s22p63s23p3
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5.2
Electron Arrangement in
Atoms
>
Exceptional Electron Configurations
Exceptional Electron Configurations
Why do actual electron configurations
for some elements differ from those
assigned using the aufbau principle?
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5.2
Electron Arrangement in
Atoms
>
Exceptional Electron Configurations
Some actual electron configurations
differ from those assigned using the
aufbau principle because half-filled
sublevels are not as stable as filled
sublevels, but they are more stable than
other configurations.
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5.2
Electron Arrangement in
Atoms
>
Exceptional Electron Configurations
Exceptions to the aufbau
principle are due to subtle
electron-electron
interactions in orbitals with
very similar energies.
Copper has an electron
configuration that is an
exception to the aufbau
principle.
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Electron Arrangement in
Atoms
>
Exception
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5.2 Section Quiz.
Assess students’ understanding
of the concepts in Section 5.2.
Continue to:
-or-
Launch:
Section Quiz
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5.2 Section Quiz.
1. Identify the element that corresponds to the
following electron configuration: 1s22s22p5.
a. F
b. Cl
c. Ne
d. O
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5.2 Section Quiz.
2. Write the electron configuration for the atom N.
a. 1s22s22p5
b. 1s22s22p3
c. 1s22s1p2
d. 1s22s22p1
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5.2 Section Quiz.
3. The electron configurations for some
elements differ from those predicted by the
aufbau principle because the
a. the lowest energy level is completely filled.
b. none of the energy levels are completely
filled.
c. half-filled sublevels are less stable than
filled energy levels.
d. half-filled sublevels are more stable than
`
some other arrangements.
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