Transcript Document
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5.2 Electron Arrangement in Atoms >
Chapter 5 Electrons In Atoms 5.1 Revising the Atomic Model
5.2 Electron Arrangement in Atoms
5.3 Atomic Emission Spectra and the Quantum Mechanical Model Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
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5.2 Electron Arrangement in Atoms > CHEMISTRY & YOU What gives gas-filled lights their colors?
An electric current passing through the gas in each glass tube makes the gas glow with its own characteristic color.
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5.2 Electron Arrangement in Atoms >
Light and Atomic Emission Spectra
Light and Atomic Emission Spectra
What causes atomic emission spectra?
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5.2 Electron Arrangement in Atoms >
Light and Atomic Emission Spectra
Atomic Emission Spectra When atoms absorb energy, their electrons move to higher energy levels. These electrons lose energy by emitting light when they return to their lower
(ground)
energy levels.
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5.2 Electron Arrangement in Atoms >
Light and Atomic Emission Spectra
Atomic Emission Spectra
A prism separates light into the colors it contains. White light produces a rainbow of colors.
5 Screen Light bulb Slit Prism Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Light and Atomic Emission Spectra
Atomic Emission Spectra
Light from a helium lamp produces discrete lines.
Helium lamp Screen Slit Prism Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
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5.2 Electron Arrangement in Atoms >
An Explanation of Atomic Spectra
An Explanation of Atomic Spectra
How is the color of light emitted by an atom related to changes of electron energies?
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5.2 Electron Arrangement in Atoms >
An Explanation of Atomic Spectra
The light emitted by an electron moving from a higher to a lower energy level has a color directly proportional to the energy change of the electron.
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5.2 Electron Arrangement in Atoms >
An Explanation of Atomic Spectra When an electron has its lowest possible energy, the atom is in its
ground state
.
• In the ground state, the principal quantum number (
n
) is equal to it’s energy level.
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5.2 Electron Arrangement in Atoms >
An Explanation of Atomic Spectra When an electron has its lowest possible energy, the atom is in its
ground state
.
• In the ground state, the principal quantum number (
n
) is equal to it’s energy level.
• Excitation of the electron by absorbing energy raises the atom to an excited state with
n
= 2, 3, 4 and so forth.
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5.2 Electron Arrangement in Atoms >
An Explanation of Atomic Spectra 11 When an electron has its lowest possible energy, the atom is in its
ground state
.
• In the ground state, the principal quantum number (
n
) is equal to it’s energy level.
• Excitation of the electron by absorbing energy raises the atom to an excited state with
n
= 2, 3, 4 and so forth.
• A quantum of energy in the form of light is emitted when the electron drops back to a lower energy level.
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An Explanation of Atomic Spectra Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
5.2 Electron Arrangement in Atoms >
Light and Atomic Emission Spectra
Atomic Emission Spectra
• The energy absorbed by an electron for it to move from its current energy level to a higher energy level is identical to the energy of the light emitted by the electron as it drops back to its original energy level.
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5.2 Electron Arrangement in Atoms >
Light and Atomic Emission Spectra
Atomic Emission Spectra
• The energy absorbed by an electron for it to move from its current energy level to a higher energy level is identical to the energy of the light emitted by the electron as it drops back to its original energy level. • The wavelengths of the spectral lines are characteristic of the element, and they make up the
atomic emission spectrum
of the element.
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5.2 Electron Arrangement in Atoms >
Light and Atomic Emission Spectra 15
Atomic Emission Spectra
• The energy absorbed by an electron for it to move from its current energy level to a higher energy level is identical to the energy of the light emitted by the electron as it drops back to its original energy level. • The wavelengths of the spectral lines are characteristic of the element, and they make up the
atomic emission spectrum
of the element.
• No two elements have the same emission spectrum.
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5.2 Electron Arrangement in Atoms > CHEMISTRY & YOU
16
What makes the electron configuration of an atom stable?
Having a completely filled valence level. Energy and stability play an important role in determining how electrons are configured in an atom.
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5.2 Electron Arrangement in Atoms >
Electron Configurations
Electron Configurations
What are the three rules for writing the electron configurations of elements?
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5.2 Electron Arrangement in Atoms >
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 The ways in which electrons are arranged in various orbitals around the nuclei of atoms are called
electron configurations
.
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5.2 Electron Arrangement in Atoms >
Electron Configurations
Aufbau Principle
6
s
5
s
4
s
6
p
5
p
4
p
3
p
5
d
4
d
3
d
4
f
3
s
20 2
s
1
s
2
p
According to the
aufbau principle
, electrons occupy the orbitals of lowest energy first. In the aufbau diagram, each box represents an atomic orbital.
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5.2 Electron Arrangement in Atoms >
Electron Configurations
Aufbau Principle
6
s
5
s
4
s
6
p
5
p
4
p
3
p
3
s
2
p
2
s
1
s
5
d
4
d
3
d
4
f
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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5.2 Electron Arrangement in Atoms >
Electron Configurations 22
Aufbau Principle
6
s
5
s
4
s
6
p
5
p
4
p
3
p
3
s
2
p
2
s
1
s
5
d
4
d
3
d
4
f
The range of energy levels within a principal energy level can overlap the energy levels of another principal level. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
5.2 Electron Arrangement in Atoms >
Electron Configurations
Pauli Exclusion Principle
• According to the
Pauli exclusion principle
, an atomic orbital may describe at most two electrons. 23 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
5.2 Electron Arrangement in Atoms >
Electron Configurations
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.
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5.2 Electron Arrangement in Atoms >
Electron Configurations
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.
• The electron spins must be paired to fill the orbital.
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5.2 Electron Arrangement in Atoms >
Electron Configurations
Pauli Exclusion Principle
•
Spin
is a quantum mechanical property of electrons and may be thought of as clockwise or counterclockwise.
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5.2 Electron Arrangement in Atoms >
Electron Configurations
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 ).
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5.2 Electron Arrangement in Atoms >
Electron Configurations
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 .
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5.2 Electron Arrangement in Atoms >
Electron Configurations
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.
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5.2 Electron Arrangement in Atoms >
Electron Configurations
Hund’s Rule
Three electrons would occupy three orbitals of equal energy as follows.
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5.2 Electron Arrangement in Atoms >
Electron Configurations
Hund’s Rule
Three electrons would occupy three orbitals of equal energy as follows.
If more electrons are needing to be placed in those orbitals, then they would be paired starting with the electron in the first orbital.
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5.2 Electron Arrangement in Atoms >
Electron Configurations Look at the orbital filling diagram of the oxygen atom. 32 • An oxygen atom contains eight electrons.
Electron Configurations of Selected Elements Element 1s 2s 2p
x
2p
y
2p
z
3s Electron configuration
H 1
s
1 He Li C N
O
F Ne Na 1
s
2 1
s
2 2
s
1 1
s
2 2
s
2 2
p
2 1
s
2 2
s
2 2
p
3
1s 2 2s 2 2p 4
1
s
2 2
s
2 2
p
5 1
s
2 2
s
2 2
p
6 1
s
2 2
s
2 2
p
6 3
s
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5.2 Electron Arrangement in Atoms >
Electron Configurations Look at the orbital filling diagram of the oxygen atom. 33 • The 1
s
orbital has two electrons of opposite spin.
Electron Configurations of Selected Elements Element 1s 2s 2p
x
2p
y
2p
z
3s Electron configuration
H 1
s
1 He Li C N O F Ne Na 1
s
2 1
s
2 2
s
1 1
s
2 2
s
2 2
p
2 1
s
2 2
s
2 2
p
3
1s 2 2s 2 2p 4
1
s
2 2
s
2 2
p
5 1
s
2 2
s
2 2
p
6 1
s
2 2
s
2 2
p
6 3
s
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5.2 Electron Arrangement in Atoms >
Electron Configurations Look at the orbital filling diagram of the oxygen atom. 34 • The 1
s
orbital has two electrons of opposite spin.
• The 2
s
orbital also has two electrons of opposite spin.
Electron Configurations of Selected Elements Element 1s 2s 2p
x
2p
y
2p
z
3s Electron configuration
H 1
s
1 He Li C N
O
F Ne Na 1
s
2 1
s
2 2
s
1 1
s
2 2
s
2 2
p
2 1
s
2 2
s
2 2
p
3
1s 2 2s 2 2p 4
1
s
2 2
s
2 2
p
5 1
s
2 2
s
2 2
p
6 1
s
2 2
s
2 2
p
6 3
s
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5.2 Electron Arrangement in Atoms >
Electron Configurations Look at the orbital filling diagram of the oxygen atom. • Each of the three 2
p
has one orbitals electron. The remaining electron now pairs with an electron occupying one of the 2
p
orbitals.
Element
H He Li C N
O
F Ne Na
Electron Configurations of Selected Elements 1s 2s 2p
x
2p
y
2p
z
3s Electron configuration
1
s
1 1
s
2 1
s
2 2
s
1 1
s
2 2
s
2 2
p
2 1
s
2 2
s
2 2
p
3
1s 2 2s 2 2p 4
1
s
2 2
s
2 2
p
5 1
s
2 2
s
2 2
p
6 1
s
2 2
s
2 2
p
6 3
s
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5.2 Electron Arrangement in Atoms >
Electron Configurations • A method for showing the electron configuration of an atom involves writing the energy level and the symbol for every sublevel occupied by an electron.
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5.2 Electron Arrangement in Atoms >
Electron Configurations • A 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.
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5.2 Electron Arrangement in Atoms >
Electron Configurations • For hydrogen, with one electron in a 1
s
orbital, the electron configuration is written
1s 1
.
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5.2 Electron Arrangement in Atoms >
Electron Configurations • For hydrogen, with one electron in a 1
s
orbital, the electron configuration is written
1s 1
.
• For oxygen, with two electrons in a 1
s
orbital, two electrons in a 2
s
orbital, and four electrons in 2
p
orbitals, the electron configuration is
1s 2 2s 2 2p 4
.
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5.2 Electron Arrangement in Atoms >
Electron Configurations • For hydrogen, with one electron in a 1
s
orbital, the electron configuration is written
1s 1
.
• For oxygen, with two electrons in a 1
s
orbital, two electrons in a 2
s
orbital, and four electrons in 2
p
orbitals, the electron configuration is
1s 2 2s 2 2p 4
.
Note: The sum of the superscripts equals the number of electrons in the atom.
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Explain why the correct electron configuration of oxygen is 1s
2
2s
2
2p
4
and not 1s
2
2s
2
2p
3
3s
1
.
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Explain why the correct electron configuration of oxygen is 1s
2
2s
2
2p
4
and not 1s
2
2s
2
2p
3
3s
1
.
The 2p orbitals are lower in energy than the 3s orbital, so they will be completely filled before any electrons will be found in the 3s orbital. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
5.2 Electron Arrangement in Atoms > Sample
Problem
Writing Electron Configurations
The atomic number of chlorine is 17. Write the electron configuration of a chlorine atom.
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Sample
Problem
1 Analyze
Identify the relevant concepts.
Chlorine has 17 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.
When writing electron configurations, the sublevels within the same principal energy level are written together.
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Sample
Problem
2 Solve
Apply the concepts to this problem.
• Use the aufbau diagram to place electrons in the orbital with the lowest energy (1
s
) first.
1
s
2
s
2
p
3
s
3
p
4
s
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5.2 Electron Arrangement in Atoms > Sample
Problem
2 Solve
Apply the concepts to this problem.
• Use the aufbau diagram to place electrons in the orbital with the lowest energy (1
s
) first.
• Continue placing electrons in each orbital with the next higher energy level.
1
s
2
s
2
p
3
s
3
p
4
s
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Sample
Problem
2 Solve
Apply the concepts to this problem.
Write the electron configuration.
• The electron configuration of chlorine is 1
s
2
2
s
2
2
p
6
3
s
2
3
p
5
.
• The
superscripts
add up to the number of electrons found in a chlorine atom (
17
).
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5.2 Electron Arrangement in Atoms >
Electron Configurations
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.
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5.2 Electron Arrangement in Atoms >
Electron Configurations
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 continued, 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 49
2 2s 2 2p 6 3s 2 3p 6 3d 9 4s
2
or
Cr 1s
2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 4
Cu 1s
2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 9
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5.2 Electron Arrangement in Atoms >
Electron Configurations 50
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 or
Cr 1s
2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5
Cu 1s
2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 10
• These arrangements give chromium a half-filled sublevel.
d
sublevel and copper a filled
d
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5.2 Electron Arrangement in Atoms >
Electron Configurations
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 are more stable than other configurations.
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What is the correct electron configuration of a sulfur atom?
A.
1
s
2 2
s
2 2
p
4 3
s
2 3
p
6
B.
1
s
2 2
s
2 2
p
6 3
s
2 3
p
3
C.
1
s
2 2
s
2 2
p
6 3
s
2 3
p
4
D.
1
s
2 2
s
2 2
p
6 3
s
6 3
p
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What is the correct electron configuration of a sulfur atom?
A.
1
s
2 2
s
2 2
p
4 3
s
2 3
p
6
B.
1
s
2 2
s
2 2
p
6 3
s
2 3
p
3
C. 1s
2
2s
2
2p
6
3s
2
3p
4
D.
1
s
2 2
s
2 2
p
6 3
s
6 3
p
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5.2 Electron Arrangement in Atoms >
Electron Configurations
Shorthand Method to Electron Configuration
1.)
Write the chemical symbol of the Noble gas at the end of the row above the one containing the element you are working on.
2.)
Place brackets [ ] around that symbol.
3.)
Write the electron configuration for the last row containing the element you are working on.
ex.:
manganese 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5
4s 2 3d 5
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5.2 Electron Arrangement in Atoms >
Electron Configurations 55
Every electron has four (4) quantum numbers assigned to it.
The Pauli Exclusion Principle says “No two electrons can have the exact same quantum numbers.”
1.)
The first number is the principle quantum number and corresponds to the electron’s energy level.
(n)
2.)
The second number is the angular momentum {azimuthal} and corresponds to the orbital shape.
( ℓ)
3.)
The third number is the magnetic and corresponds to the orbital order or sequence.
(m ℓ )
4.)
The fourth number is the spin and corresponds to the direction of motion (clockwise or counter clockwise).
(m s )
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5.2 Electron Arrangement in Atoms >
Electron Configurations Quantum numbers assigned to electrons.
Summary of Quantum Numbers and Orbital Designations
56
1.) Principal Energy Level
(n)
1 2 3 4
2.) Angular Momentum (Azimuthal)
( ℓ)
0 0 1 2 3 0 1 0 1 2
3.) Magnetic
(m ℓ )
4.) Spin
(m s )
Maximum Number of Electrons
0 0 -1, 0 , +1 0 -1, 0, +1 -2, -1, 0, +1, +2 0 -1, 0, +1 -2, -1, 0, +1, +2 -3, -2, -1, 0, +1, +2, +3 ± ½ ± ± ± ± ± ± ± ± ± ½ ½ ½ ½ ½ ½ ½ ½ ½ 2 8 18 32 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
What are the four (4) quantum numbers associated with manganese.
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What are the four (4) quantum numbers associated with manganese.
• n = 4 • ℓ = 2 • m ℓ = +2 • m s = +½ Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
5.2 Electron Arrangement in Atoms >
Key Concepts and Key Equations When atoms absorb energy, their electrons move to higher energy levels. These electrons lose energy by emitting light when they return to lower energy levels.
The light emitted by an electron moving from a higher to a lower energy level has a color directly proportional to the energy change of the electron.
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 > END OF 5.2
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