Chapter 7
CHAPTER 7: THE QUANTUM-MECHANICAL MODEL OF THE ATOM
CLASS NOTES FOR CHEMISTRY 1311
Compiled by Dr. Ann Cartwright(Updated 2017)
CHEMISTRY: A MOLECULAR APPROACH
4th EDITION
NIVALDO J. TRO
7.1 Schrodinger’s Cat
Electrons are super small, yet they determine many of the chemical and physical properties of
atoms. Very small electrons behave differently than large substances in the world we observe
with our eyes.
7.2 The Nature of Light
Light was found to have many characteristics in common with electrons. The main
characteristic was the wave-particle duality of light. Certain properties of light are best
described by thinking of it as a wave, while other properties are best described by thinking of it
as a particle.
7.3 Atomic Spectroscopy and the Bohr Model
In the Bohr model of the atom electrons travel around the nucleus in circular orbits like planets
around the sun. This is no longer accepted, but it helped explain emission spectra. After an
atom absorbs energy in the form of heat, light or electricity, it often re-emits energy as light of a
particular color depending on what type of atom it is. Bohr explained this as an electron
absorbs energy and goes to a higher energy level and then emits energy when it falls back to a
lower level.
Quantized: something is in discrete steps
The atom is said to be quantized because the energy levels (shells) for the electrons are
thought to be discrete energy differences apart. If energy such as heat energy is used to excite
electrons, the electrons absorb energy and go to a higher energy level. The electron is not as
stable in the higher or excited state and drops back to the original state also called ground
state. The energy is released and often in the form of light. Since for certain atoms there are
certain colors of light emitted, which means certain wavelengths of light, or light of a certain
energy is emitted. This was interpreted to mean that the energy levels are discrete steps apart.
Therefore, we say the atom is quantized.
Nucleus (center of the atom) l I I l (These are energy levels.)
68
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, Chapter 7
n = 1 2 3 4 These would be the first fourmajor
energy levels in the Bohr atom.
7.4 The Wave Nature of Matter: The de Broglie Wavelength, the Uncertainty Principle, and
Interterminacy
Orbital: a probability distribution map showing where the electron is likely to be found.
Einstein’s idea that light can exhibit both wave properties and particle properties suggested to
de Broglie that very small particles such as electrons could also display both wave and particle
properties.
Electrons appear to have particle behavior or wave behavior depending on the experiment
done.
Heisenberg’s uncertainty principle: The more accurately we know the position of an electron
the less accurately we know it velocity and vice versa.
I strongly suggest electron configurations be covered before quantum numbers and quantum
numbers will be easier for the students. Electron configurations are found in Chapter 8.
7.5 Quantum Mechanics and the Atom
Quantum numbers-- there are four. Those four are unique for each electron in a particular atom
and gives us information. Quantum comes from the thought that the atom is quantized. The
energy levels are at discrete energy steps apart.
This is a simplified discussion that is sufficient for our purposes.
Each electron in an atom has four quantum numbers associated with it. Each electron has its
own four quantum numbers and no two electrons in the same atom have the same four
numbers. We can think of these four quantum numbers as an address for the electron.
1st quantum number or principal quantum number: n Can have values of 1,2,3,4,∙∙∙ (They
are integers) and tells us the overall size and energy of an orbital. It tells us the major energy
level. If n = 1, the electron is on the first major energy level. If n = 2, the electron is on the
second major energy level.
69
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https://www.coursehero.com/file/24126444/TRO-CHAPTER-7-CLASS-NOTES-20172docx/
CHAPTER 7: THE QUANTUM-MECHANICAL MODEL OF THE ATOM
CLASS NOTES FOR CHEMISTRY 1311
Compiled by Dr. Ann Cartwright(Updated 2017)
CHEMISTRY: A MOLECULAR APPROACH
4th EDITION
NIVALDO J. TRO
7.1 Schrodinger’s Cat
Electrons are super small, yet they determine many of the chemical and physical properties of
atoms. Very small electrons behave differently than large substances in the world we observe
with our eyes.
7.2 The Nature of Light
Light was found to have many characteristics in common with electrons. The main
characteristic was the wave-particle duality of light. Certain properties of light are best
described by thinking of it as a wave, while other properties are best described by thinking of it
as a particle.
7.3 Atomic Spectroscopy and the Bohr Model
In the Bohr model of the atom electrons travel around the nucleus in circular orbits like planets
around the sun. This is no longer accepted, but it helped explain emission spectra. After an
atom absorbs energy in the form of heat, light or electricity, it often re-emits energy as light of a
particular color depending on what type of atom it is. Bohr explained this as an electron
absorbs energy and goes to a higher energy level and then emits energy when it falls back to a
lower level.
Quantized: something is in discrete steps
The atom is said to be quantized because the energy levels (shells) for the electrons are
thought to be discrete energy differences apart. If energy such as heat energy is used to excite
electrons, the electrons absorb energy and go to a higher energy level. The electron is not as
stable in the higher or excited state and drops back to the original state also called ground
state. The energy is released and often in the form of light. Since for certain atoms there are
certain colors of light emitted, which means certain wavelengths of light, or light of a certain
energy is emitted. This was interpreted to mean that the energy levels are discrete steps apart.
Therefore, we say the atom is quantized.
Nucleus (center of the atom) l I I l (These are energy levels.)
68
This study source was downloaded by 100000839006816 from CourseHero.com on 02-14-2022 04:46:53 GMT -06:00
https://www.coursehero.com/file/24126444/TRO-CHAPTER-7-CLASS-NOTES-20172docx/
, Chapter 7
n = 1 2 3 4 These would be the first fourmajor
energy levels in the Bohr atom.
7.4 The Wave Nature of Matter: The de Broglie Wavelength, the Uncertainty Principle, and
Interterminacy
Orbital: a probability distribution map showing where the electron is likely to be found.
Einstein’s idea that light can exhibit both wave properties and particle properties suggested to
de Broglie that very small particles such as electrons could also display both wave and particle
properties.
Electrons appear to have particle behavior or wave behavior depending on the experiment
done.
Heisenberg’s uncertainty principle: The more accurately we know the position of an electron
the less accurately we know it velocity and vice versa.
I strongly suggest electron configurations be covered before quantum numbers and quantum
numbers will be easier for the students. Electron configurations are found in Chapter 8.
7.5 Quantum Mechanics and the Atom
Quantum numbers-- there are four. Those four are unique for each electron in a particular atom
and gives us information. Quantum comes from the thought that the atom is quantized. The
energy levels are at discrete energy steps apart.
This is a simplified discussion that is sufficient for our purposes.
Each electron in an atom has four quantum numbers associated with it. Each electron has its
own four quantum numbers and no two electrons in the same atom have the same four
numbers. We can think of these four quantum numbers as an address for the electron.
1st quantum number or principal quantum number: n Can have values of 1,2,3,4,∙∙∙ (They
are integers) and tells us the overall size and energy of an orbital. It tells us the major energy
level. If n = 1, the electron is on the first major energy level. If n = 2, the electron is on the
second major energy level.
69
This study source was downloaded by 100000839006816 from CourseHero.com on 02-14-2022 04:46:53 GMT -06:00
https://www.coursehero.com/file/24126444/TRO-CHAPTER-7-CLASS-NOTES-20172docx/
