Electron arrangement in atoms

Rules for determining how electrons fill their energy levels.

1. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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Chapter 5
Electron Arrangement
in Atoms

2. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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What are the three rules for
writing the electron
configurations of elements?
Electron Configurations
Electron ConfigurationsElectron Configurations

3. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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The ways in which electrons are arranged
in various orbitals around the nuclei of
atoms are called electron configurations.
Electron ConfigurationsElectron Configurations

4. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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Three rules—the aufbau
principle, the Pauli exclusion
principle, and Hund’s rule—tell
you how to find the electron
configurations of atoms.
Electron ConfigurationsElectron Configurations

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Aufbau Principle
Electron ConfigurationsElectron Configurations
According to the aufbau principle,
electrons occupy the orbitals of lowest
energy first. In the aufbau diagram,
each box represents an atomic orbital.
I
n
c
r
e
a
s
i
n
g

e
n
e
r
g
y
6s
5s
4s
3s
2s
1s
6p
5p
5d
4p
4d
4f
3p
3d
2p

6. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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Aufbau Principle
Electron ConfigurationsElectron Configurations
I
n
c
r
e
a
s
i
n
g

e
n
e
r
g
y
6s
5s
4s
3s
2s
1s
6p
5p
5d
4p
4d
4f
3p
3d
2p
The aufbau diagram shows the
relative energy levels of the various
atomic orbitals. Orbitals of greater
energy are higher on the diagram.

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Aufbau Principle
Electron ConfigurationsElectron Configurations
I
n
c
r
e
a
s
i
n
g

e
n
e
r
g
y
6s
5s
4s
3s
2s
1s
6p
5p
5d
4p
4d
4f
3p
3d
2p
The range of energy levels within a
principal energy level can overlap
the energy levels of another
principal level.

8. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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Pauli Exclusion Principle
•According to the Pauli exclusion principle,
an atomic orbital may describe at most two
electrons.
•To occupy the same orbital, two electrons
must have opposite spins; that is, the
electron spins must be paired.
Electron ConfigurationsElectron Configurations

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Pauli Exclusion Principle
•Spin is a quantum mechanical property of
electrons and may be thought of as
clockwise or counterclockwise.
•A vertical arrow indicates an electron and its
direction of spin (­ or ¯).
•An orbital containing paired electrons is
written as .
Electron ConfigurationsElectron Configurations

10. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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Hund’s Rule
According to Hund’s rule, 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.
Electron ConfigurationsElectron Configurations

11. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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Hund’s Rule
Three electrons would occupy three
orbitals of equal energy as follows.
Electron ConfigurationsElectron Configurations

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Hund’s Rule
Three electrons would occupy three
orbitals of equal energy as follows.
Electrons then occupy each orbital
so that their spins are paired with the
first electron in the orbital.
Electron ConfigurationsElectron Configurations

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Electron ConfigurationsElectron Configurations
Look at the orbital filling diagram of the oxygen atom.
Electron Configurations of Selected Elements
Element1s2s2p
x
2p
y
2p
z3s
Electron
configuration
H 1s
1
He 1s
2
Li 1s
2
2s
1
C 1s
2
2s
2
2p
2
N 1s
2
2s
2
2p
3
O 1s
2
2s
2
2p
4
F 1s
2
2s
2
2p
5
Ne 1s
2
2s
2
2p
6
Na 1s
2
2s
2
2p
6
3s
1
•An oxygen
atom contains
eight
electrons.

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Electron ConfigurationsElectron Configurations
Look at the orbital filling diagram of the oxygen atom.
Electron Configurations of Selected Elements
Element1s2s2p
x
2p
y
2p
z3s
Electron
configuration
H 1s
1
He 1s
2
Li 1s
2
2s
1
C 1s
2
2s
2
2p
2
N 1s
2
2s
2
2p
3
O 1s
2
2s
2
2p
4
F 1s
2
2s
2
2p
5
Ne 1s
2
2s
2
2p
6
Na 1s
2
2s
2
2p
6
3s
1
•The 1s orbital
has two
electrons of
opposite spin.

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Electron ConfigurationsElectron Configurations
Look at the orbital filling diagram of the oxygen atom.
Electron Configurations of Selected Elements
Element1s2s2p
x
2p
y
2p
z3s
Electron
configuration
H 1s
1
He 1s
2
Li 1s
2
2s
1
C 1s
2
2s
2
2p
2
N 1s
2
2s
2
2p
3
O 1s
2
2s
2
2p
4
F 1s
2
2s
2
2p
5
Ne 1s
2
2s
2
2p
6
Na 1s
2
2s
2
2p
6
3s
1
•The 1s orbital
has two
electrons of
opposite spin.
•The 2s orbital
also has two
electrons of
opposite spin.

16. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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Electron ConfigurationsElectron Configurations
Look at the orbital filling diagram of the oxygen atom.
•Each of the
three 2p orbitals
has one
electron. The
remaining
electron now
pairs with an
electron
occupying one
of the 2p
orbitals.
Electron Configurations of Selected Elements
Element1s2s2p
x
2p
y
2p
z3s
Electron
configuration
H 1s
1
He 1s
2
Li 1s
2
2s
1
C 1s
2
2s
2
2p
2
N 1s
2
2s
2
2p
3
O 1s
2
2s
2
2p
4
F 1s
2
2s
2
2p
5
Ne 1s
2
2s
2
2p
6
Na 1s
2
2s
2
2p
6
3s
1

17. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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•A convenient shorthand method for showing
the electron configuration of an atom involves
writing the energy level and the symbol for
every sublevel occupied by an electron.
Electron ConfigurationsElectron Configurations

18. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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•A convenient shorthand method for showing
the electron configuration of an atom involves
writing the energy level and the symbol for
every sublevel occupied by an electron.
•You indicate the number of electrons
occupying that sublevel with a superscript.
Electron ConfigurationsElectron Configurations

19. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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•For hydrogen, with one electron in a 1s
orbital, the electron configuration is
written 1s
1
.
Electron ConfigurationsElectron Configurations

20. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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•For hydrogen, with one electron in a 1s
orbital, the electron configuration is
written 1s
1
.
•For oxygen, with two electrons in a 1s
orbital, two electrons in a 2s orbital, and
four electrons in 2p orbitals, the electron
configuration is 1s
2
2s
2
2p
4
.
Electron ConfigurationsElectron Configurations

21. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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•For hydrogen, with one electron in a 1s
orbital, the electron configuration is
written 1s
1
.
•For oxygen, with two electrons in a 1s
orbital, two electrons in a 2s orbital, and
four electrons in 2p orbitals, the electron
configuration is 1s
2
2s
2
2p
4
.
Electron ConfigurationsElectron Configurations
Note that the sum of the superscripts
equals the number of electrons in the
atom.

22. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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Sample Problem 5.1
Analyze Identify the relevant concepts.
Phosphorus has 15 electrons. There is
a maximum of two electrons per
orbital. Electrons do not pair up within
an energy sublevel (orbitals of equal
energy) until each orbital already has
one electron.
1
When writing electron
configurations, the sublevels
within the same principal
energy level are written
together.

23. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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Sample Problem 5.1
SolveApply the concepts to
this problem.
•Use the aufbau diagram to place
electrons in the orbital with the lowest
energy (1s) first.
2
1s

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Sample Problem 5.1
SolveApply the concepts to
this problem.
•Use the aufbau diagram to place
electrons in the orbital with the lowest
energy (1s) first.
•Continue placing electrons in each orbital
with the next higher energy level.
2
1s2s 2p 3p3s 4s

25. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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Sample Problem 5.1
•The electron configuration of phosphorus
is 1s
2
2s
2
2p
6
3s
2
3p
3
.
•The superscripts add up to the number of
electrons.
2SolveApply the concepts to
this problem.
Write the electron configuration.

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Exceptional Electron Configurations
Electron ConfigurationsElectron Configurations
•You can obtain correct electron configurations
for the elements up to vanadium (atomic
number 23) by following the aufbau diagram for
orbital filling.

27. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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Exceptional Electron Configurations
•You can obtain correct electron configurations
for the elements up to vanadium (atomic
number 23) by following the aufbau diagram for
orbital filling.
•If you were to continue in that fashion, however,
you would assign chromium and copper the
following incorrect configurations.
Cr 1s
2
2s
2
2p
6
3s
2
3p
6
3d
4
4s
2
Cu 1s
2
2s
2
2p
6
3s
2
3p
6
3d
9
4s
2
Electron ConfigurationsElectron Configurations

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Exceptional Electron Configurations
•The correct electron configurations are as
follows:
Cr 1s
2
2s
2
2p
6
3s
2
3p
6
3d
5
4s
1
Cu 1s
2
2s
2
2p
6
3s
2
3p
6
3d
10
4s
1
•These arrangements give chromium a
half-filled d sublevel and copper a filled d
sublevel.
Electron ConfigurationsElectron Configurations

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Exceptional Electron Configurations
Some actual electron configurations
differ from those assigned using the
aufbau principle because although half-
filled sublevels are not as stable as
filled sublevels, they are more stable
than other configurations.
Electron ConfigurationsElectron Configurations

30. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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What is the correct electron
configuration of a sulfur atom?
A. 1s
2
2s
2
2p
4
3s
2
3p
6
B. 1s
2
2s
2
2p
6
3s
2
3p
3
C. 1s
2
2s
2
2p
6
3s
2
3p
4
D. 1s
2
2s
2
2p
6
3s
6
3p
2

31. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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What is the correct electron
configuration of a sulfur atom?
A. 1s
2
2s
2
2p
4
3s
2
3p
6
B. 1s
2
2s
2
2p
6
3s
2
3p
3
C. 1s
2
2s
2
2p
6
3s
2
3p
4
D. 1s
2
2s
2
2p
6
3s
6
3p
2

32. 5.2 Electron Arrangement in Atoms >5.2 Electron Arrangement in Atoms >
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Key ConceptKey Concept
Three rules—the aufbau principle, the Pauli
exclusion principle, and Hund’s rule—tell you
how to find the electron configurations of
atoms.