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Chapter 7

book notes for chapter 7


Department
Chemistry
Course Code
CHMA10H3
Professor
Ann Verner
Chapter
7

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Chapter 7: The Quantum-Mechanical Model of an Atom
Quantum Mechanics: The Theory That Explains the Behavior of the Absolutely Small
Quantum-Mechanical Model: a model that explains how electrons exist in atoms and how
those electrons determine the chemical and physical properties of elements.
The Nature of Light
Electromagnetic Radiation: a type of energy embodied in oscillating electric and magnetic
fields.
oElectric Field: a region of space where an electrically charged particle experiences a
force (proton or electron).
oMagnetic Field: a region of space where a magnetic particle experiences a force
(magnet).
Light travels faster than sound thats why we see lightning before we hear thunder.
Amplitude: the vertical height of a crest or depth of a trough.
oThe greater the amplitude, the greater the intensity or brightness of the light.
Wavelength ( ): the distance between adjacent crests or any two analogous points.
oThe amplitude and wavelength can vary independently of one another.
Frequency (v): the number of cycles or wave crests that pass through a stationary point in a
given period of time (in Hertz or s-1).
oThe frequency of a wave is directly proportional to the speed at which the wave is
travelling.
oFrequency is inversely proportional to the wavelength.
ov = c/
For visible light, light that can be seen by the human eye, wavelength or frequency
determines color.
oRed has the longest wavelength of visible light and violet has the shortest
wavelength.
oWhen a substance absorbs some colors while reflecting others, it appears colored.
oA red shirt appears red because it reflects red light while absorbing most of the other
colors.
Electromagnetic Spectrum: all wavelengths of electromagnetic radiation.
oA short wavelength has greater energy than a long wavelength.
oLow to high energy or longer to shorter wavelength: radio, microwave, infrared,
visible light (red to violet), ultraviolet, x-ray and then gamma rays.
Interference: waves interact with each other that cancel each other out or build each other
up, depending on their alignment upon interaction.
oConstructive Interference: if two waves of equal amplitude are in phase when they
interact, they align with overlapping crests, a wave twice the amplitude (bright line).
oDestructive Interference: if two waves of equal amplitude are completely out of phase
when they interact, they align so that the crest from one source overlaps with the
trough from the other source (dark line).
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Diffraction: when a wave encounters an obstacle or a slit that is comparable in size to its
wavelength, it bends or diffracts around it.
Photoelectric Effect: the observation that many metals emit electrons when light shines upon
them.
oE = hv where h is 6.626 x 10-34 Js.
oPhoton: a packet of light that is composed of light energy.
oE = hc/
oThreshold Frequency Condition: hv = where is the binding energy of emitted 
photon.
Low-frequency light does not eject electrons because no single photon has the
minimum energy necessary to dislodge the electron.
Increasing the frequency of the light, even a low intensity, increases the
energy of each photon, allowing the photons to dislodge electrons with no lag
time.
oKE = hv
oWave-Particle Duality of Light: light sometimes appears to behave like a wave and at
other times, it behaves like a particle.
oThe shortest wavelength of light must correspond to the photoelectrons with greatest
kinetic energy and the longest wavelength of light must correspond to the instance
where no photoelectrons were observed.
Atomic Spectroscopy and the Bohr Model
Atomic Spectroscopy: the study of the electromagnetic radiation absorbed and emitted by
atoms.
oWhen an atom absorbs energy (heat, light or electricity), it often reemits that energy
as light.
Emission Spectrum: separating light emitted by a single element in a glass tube into its
constituent wavelengths by passing it through a prism.
oThe emission spectrum of a particular element is always the same and can be used to
identify the element.
oWhite light spectrum is continuous, no interruptions in the intensity of light.
oHydrogen, Helium and Barium are not continuous, they consist of bright lines at
specific wavelengths with complete darkness in between.
Bohr Model: electrons travel around the nucleus in circular orbits.
oThe energy of each Bohr orbit was fixed and could exist only at specific fixed
distances from the nucleus.
oNo radiation was emitted by an electron orbiting the nucleus in a stationary state; it
was only when an electron jumped or made a transition from one stationary state to
another that radiation was emitted or absorbed.
oTransitions between stationary states that are closer together produce light of lower
energy or longer wavelength than transitions between stationary states that are
farther apart.
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