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Transcript
Ch. 5: Models of the Atom
What you need to know: Chapter 5
•
•
•
•
Timeline pp. 128-129 (theory and people)
Definitions: quantum mechanical model,
atomic orbitals, speed of light,
electromagnetic radiation, atomic emission
spectrum (ROYGBIV), ground state, photon
Bohr model
Electron configurations
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5.1
The Development of Atomic Models
This timeline needs to be in your notes!
• The timeline shoes the development of atomic
models from 1803 to 1911.
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5.1
The Development of Atomic Models
• The timeline shows the development of atomic
models from 1913 to 1932.
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5.1 The Bohr Model
Bohr proposed that an electron is found only in
specific circular paths, or orbits, around the nucleus
Each orbit has a particular energy level; electrons must
gain or lose energy to move from one energy level to
the next
A quantum of energy is the amount of energy required
to move an electron from one energy level to another
energy level
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5.1 Quantum mechanical model
• Mathematically determined by Erwin Schrodinger
• determines the allowed energies an electron can
have and how likely it is to find the electron in
various locations around the nucleus
• An atomic orbital is often thought of as a region of
space in which there is a high probability of finding
an electron.
– Each energy sublevel corresponds to an orbital of a
different shape, which describes where the electron is
likely to be found. (s, p, and d orbitals)
(Bohr used orbits; Schrodinger used orbitals)
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5.1
Atomic Orbitals
• Different atomic orbitals are denoted by letters.
The s orbitals are spherical, and p orbitals are
dumbbell-shaped.
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5.1
Atomic Orbitals
• The numbers and kinds of atomic orbitals depend
on the energy sublevel.
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5.1
Atomic Orbitals
• The number of electrons allowed in each of the first
four energy levels are shown here.
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5.2
Electron Arrangement in Atoms
If this rock were to tumble over,
it would end up at a lower
height. It would have less
energy than before, but its
position would be more stable.
You will learn that energy and
stability play an important role
in determining how electrons
are configured in an atom.
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© Copyright Pearson Prentice Hall
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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
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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© Copyright Pearson Prentice Hall
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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, 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.
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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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Electron Arrangement in
Atoms
1. Write the electron
configuration and
orbital filling for
a. Li
b. Mg
c. Si
>
Electron Configuration and Orbital
Filling Practice
a. Li: atomic number 3
1s22s1
 _ 
b. Mg: atomic number 12
1s22s22p63s2
 _  _  _ 
c. Si: atomic number 14
1s22s22p63s23p2
 _  _  _  _ 
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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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5.3 Light
According to the wave model, light consists of
electromagnetic waves.
Electromagnetic radiation includes radio
waves, microwaves, infrared waves,
visible light, ultraviolet waves, X-rays,
and gamma rays.
All electromagnetic waves travel in a
vacuum at a speed of 2.998  108 m/s.
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5.3 Light
Sunlight consists of light with a continuous
range of wavelengths and frequencies.
When sunlight passes through a prism, the
different frequencies separate into a spectrum
of colors.
In the visible spectrum, red light has the longest
wavelength and the lowest frequency.
ROYGBIV (red, orange, yellow, green, blue,
indigo, violet)
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5.3 Light
The electromagnetic spectrum consists of
radiation over a broad band of
wavelengths.
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5.3 Atomic Spectra
Atomic Spectra
What causes atomic emission spectra?
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5.3 Atomic Spectra
When atoms absorb energy, electrons move into
higher energy levels. These electrons then
lose energy by emitting light when they return
to lower energy levels.
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5.3 Atomic Spectra
a. A prism separates light into the colors it
contains. When white light passes through a
prism, it produces a rainbow of colors.
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5.3 Atomic Spectra
a. When light from a helium lamp passes
through a prism, discrete lines are
produced.
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5.3 Atomic Spectra
a. The frequencies of light emitted by an
element separate into discrete lines to
give the atomic emission spectrum of
the element.
Mercury
Nitrogen
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5.3 An Explanation of Atomic Spectra
An Explanation of Atomic Spectra
How are the frequencies of light an atom emits
related to changes of electron energies?
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5.3 An Explanation of Atomic Spectra
a.In the Bohr model, the lone electron in the
hydrogen atom can have only certain specific
energies.
When the electron has its lowest possible energy,
the atom is in its ground state.
Excitation of the electron by absorbing energy
raises the atom from the ground state to an
excited state.
A quantum of energy in the form of light (photon) is
emitted when the electron drops back to a lower
energy level.
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5.3 An Explanation of Atomic Spectra
The light emitted by an electron moving from a
higher to a lower energy level has a
frequency directly proportional to the energy
change of the electron.
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5.3 Quantum Mechanics
Light was found to have properties similar to….
a.In 1905, Albert Einstein successfully explained
experimental data by proposing that light could
be described as quanta of energy.
The quanta behave as if they were particles.
Light quanta are called photons.
b.In 1924, De Broglie developed an equation that
predicts that all moving objects have wavelike
behavior.
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