Transcript Document

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
1
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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.
2
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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?
3
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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.
4
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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.
Screen
Light
bulb
5
Slit
Prism
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Light and Atomic
Emission Spectra
Atomic Emission Spectra
Light from a helium lamp produces
discrete lines.
Screen
Helium
lamp
Slit
Prism
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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?
7
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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.
8
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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.
9
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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.
10
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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.
• A quantum of energy in the form of light is
emitted when the electron drops back to a
lower energy level.
11
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An Explanation of
Atomic Spectra
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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.
13
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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.
14
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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.
• No two elements have the same emission
spectrum.
15
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5.2 Electron Arrangement in Atoms >
CHEMISTRY
& YOU
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.
16
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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?
17
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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.
18
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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.
19
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5.2 Electron Arrangement in Atoms > Electron Configurations
Aufbau Principle
6p
6s
5p
Increasing energy
5s
4f
4d
4p
3d
4s
3p
3s
2p
2s
1s
20
5d
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
6p
6s
5p
Increasing energy
5s
4f
4d
4p
3d
4s
3p
3s
2p
2s
1s
21
5d
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
Aufbau Principle
6p
6s
5p
Increasing energy
5s
4f
4d
4p
3d
4s
3p
3s
2p
2s
1s
22
5d
The range of energy levels within a
principal energy level can overlap
the energy levels of another
principal level.
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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.
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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.
24
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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.
25
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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.
26
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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 ).
27
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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 .
28
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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.
30
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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.
• An oxygen
atom contains
eight
electrons.
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Electron Configurations of Selected Elements
Element
1s
2s
2px 2py 2pz
3s
Electron
configuration
H
1s1
He
1s2
Li
1s22s1
C
1s22s22p2
N
1s22s22p3
O
1s22s22p4
F
1s22s22p5
Ne
1s22s22p6
Na
1s22s22p63s1
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5.2 Electron Arrangement in Atoms > Electron Configurations
Look at the orbital filling diagram of the oxygen atom.
Electron Configurations of Selected Elements
• The 1s orbital
has two
electrons of
opposite spin.
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Element
1s
2s
2px 2py 2pz
3s
Electron
configuration
H
1s1
He
1s2
Li
1s22s1
C
1s22s22p2
N
1s22s22p3
O
1s22s22p4
F
1s22s22p5
Ne
1s22s22p6
Na
1s22s22p63s1
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5.2 Electron Arrangement in Atoms > Electron Configurations
Look at the orbital filling diagram of the oxygen atom.
Electron Configurations of Selected Elements
• The 1s orbital
has two
electrons of
opposite spin.
• The 2s orbital
also has two
electrons of
opposite spin.
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Element
1s
2s
2px 2py 2pz
3s
Electron
configuration
H
1s1
He
1s2
Li
1s22s1
C
1s22s22p2
N
1s22s22p3
O
1s22s22p4
F
1s22s22p5
Ne
1s22s22p6
Na
1s22s22p63s1
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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 2p orbitals
has one
electron. The
remaining
electron now
pairs with an
electron
occupying one
of the 2p
orbitals.
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Electron Configurations of Selected Elements
Element
1s
2s
2px 2py 2pz
3s
Electron
configuration
H
1s1
He
1s2
Li
1s22s1
C
1s22s22p2
N
1s22s22p3
O
1s22s22p4
F
1s22s22p5
Ne
1s22s22p6
Na
1s22s22p63s1
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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 1s
orbital, the electron configuration is
written 1s1.
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5.2 Electron Arrangement in Atoms > Electron Configurations
• For hydrogen, with one electron in a 1s
orbital, the electron configuration is
written 1s1.
• 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 1s22s22p4.
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5.2 Electron Arrangement in Atoms > Electron Configurations
• For hydrogen, with one electron in a 1s
orbital, the electron configuration is
written 1s1.
• 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 1s22s22p4.
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
1s22s22p4 and not 1s22s22p33s1.
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Explain why the correct electron
configuration of oxygen is
1s22s22p4 and not 1s22s22p33s1.
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.
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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 (1s) first.
1s
2s
2p
3s
3p
4s
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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 (1s) first.
• Continue placing electrons in each orbital
with the next higher energy level.
1s
46
2s
2p
3s
3p
4s
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Sample Problem
2 Solve Apply the concepts to
this problem.
Write the electron configuration.
• The electron configuration of chlorine is
1s22s22p63s23p5.
• 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.
48
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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 1s22s22p63s23p63d44s2
Cu 1s22s22p63s23p63d94s2
49
or
Cr 1s22s22p63s23p64s23d4
Cu 1s22s22p63s23p64s23d9
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5.2 Electron Arrangement in Atoms > Electron Configurations
Exceptional Electron Configurations
• The correct electron configurations are as
follows:
Cr 1s22s22p63s23p63d54s1
Cu 1s22s22p63s23p63d104s1
or
Cr 1s22s22p63s23p64s13d5
Cu 1s22s22p63s23p64s13d10
• These arrangements give chromium a
half-filled d sublevel and copper a filled d
sublevel.
50
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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.
51
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What is the correct electron
configuration of a sulfur atom?
A. 1s22s22p43s23p6
B. 1s22s22p63s23p3
C. 1s22s22p63s23p4
D. 1s22s22p63s63p2
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What is the correct electron
configuration of a sulfur atom?
A. 1s22s22p43s23p6
B. 1s22s22p63s23p3
C.
2
2
6
2
4
1s 2s 2p 3s 3p
D. 1s22s22p63s63p2
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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
1s22s22p63s23p64s23d5
[ Ar ] 4s23d5
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5.2 Electron Arrangement in Atoms > Electron Configurations
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. (mℓ)
4.) The fourth number is the spin and corresponds to the
direction of motion (clockwise or counter clockwise). (ms)
55
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5.2 Electron Arrangement in Atoms > Electron Configurations
Quantum numbers assigned to electrons.
Summary of Quantum Numbers and Orbital Designations
1.) Principal
Energy Level
(n)
2.) Angular
Momentum
(Azimuthal)
(ℓ)
3.) Magnetic
(mℓ)
4.) Spin
(ms)
Maximum
Number of
Electrons
1
0
0
±½
2
2
0
1
0
-1, 0 , +1
±½
±½
8
3
0
1
2
0
-1, 0, +1
-2, -1, 0, +1, +2
±½
±½
±½
18
4
0
1
2
3
0
-1, 0, +1
-2, -1, 0, +1, +2
-3, -2, -1, 0, +1, +2, +3
±½
±½
±½
±½
32
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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
• mℓ = +2
• ms = +½
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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.
59
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5.2 Electron Arrangement in Atoms >
END OF 5.2
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