Download Electromagnetic Spectrum

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Unit 2: Electrons in the
Atom
The Beginnings of Quantum
Mechanics
• Quantum mechanics forms the foundation of
chemistry – explaining the periodic table and the
behavior of the elements in chemical bonding – as
well as providing the practical basis for lasers,
computers, and countless other applications
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The Behavior of the Very Small
• Electrons are incredibly
small
–a single speck of dust
has more electrons than
the number of people
who have ever lived on
earth
• Electron behavior
determines much of the
behavior of atoms
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A Theory that Explains Electron
Behavior
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• The quantum-mechanical model explains the
manner in which electrons exist and behave in
atoms
• It helps us understand and predict the
properties of atoms that are directly related to
the behavior of the electrons
– why some elements are metals and others are nonmetals
– why some elements gain one electron when forming an
anion, whereas others gain two
– why some elements are very reactive while others are
practically inert
– and other periodic patterns we see in the properties of
the elements
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The Nature of Light:
Its Wave Nature
• Light is a form of electromagnetic radiation
• All electromagnetic waves move through
space at the same, constant speed
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Speed of Energy Transmission
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Characterizing Waves
• The amplitude is the height of the wave
– the distance from node to crest
» or node to trough
– the amplitude is a measure of how intense the light is – the larger the
amplitude, the brighter the light
• The wavelength (l) is a measure of the distance
covered by the wave
– the distance from one crest to the next, or trough to trough
Crest –
top of the
wave
Node –
midpoint of
the wave
Trough –
bottom of
the wave
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Characterizing Waves
• The frequency (n) is the number of waves that
pass a point in a given period of time
–the number of waves = number of cycles
–units are hertz (Hz) or cycles/s = s−1
»1 Hz = 1 s−1
• The total energy is related to the amplitude of
the waves and the frequency
–the larger the amplitude, the more energy a
wave has
–the more frequently the waves strike, the
more total force there is, the more energy
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The Relationship Between
Wavelength and Frequency
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• For waves traveling at the same speed, the shorter the
wavelength, the more frequently they pass
c  ln
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•λ = Wavelength. Units of
meters.
•ν = frequency. Units of
hertz (Hz) or 1/sec.
•c= speed of light
constant. 3.0 x 108 m/s
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Example:
• The wavelength of a red light is 5.00 x 10-6
meters. What is the frequency?
Color
• The color of light is determined
by its wavelength
– or frequency
• White light is a mixture of all the
colors of visible light
– a spectrum
– RedOrangeYellowGreenBlueViolet
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Amplitude & Wavelength
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The Electromagnetic Spectrum
• Electromagnetic spectrum- all electromagnetic
radiation, arranged according to increasing
wavelength.
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Thermal Imaging using Infrared Light
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Sunburns Caused by High-Energy
UV Radiation
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Using High-Energy Radiation
to Kill Cancer Cells
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Facts about Electromagnetic Radiation
• The size of a radio wavelength (crest to crest) is
approximately the length of a football field. The
size of a gamma ray wavelength is
approximately the size of a nucleus of an atom.
• X-rays have enough energy to damage human
cells which is why lead vests are worn.
• The visible part of the spectrum is the only part
that can be seen with the human eye. However,
other animals can see parts of the spectrum that
humans can’t. For example, a large number of
insects can see ultraviolet (UV) light.
• Gamma rays are given off by stars, and by some
radioactive substances. Lead or concrete is
needed in order to block them out.
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Energy and Frequency
relationship
E  hn
• E= energy. Units of J
• h= Planck’s constant (6.626x10-34 J.s).
This number does not change.
• v= frequency. Units of Hz or 1/sec.
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Example:
• A photon of light has a frequency of 1.1 x 1010 Hz. What
is the energy of this photon?
Practice – Order the following types
of electromagnetic radiation:
microwaves, gamma rays, green
light, red light, ultraviolet light
• By wavelength (short to long)
gamma < UV < green < red < microwaves
• By frequency (low to high)
microwaves < red < green < UV < gamma
• By energy (least to most)
microwaves < red < green < UV < gamma
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Photoelectric Effect
• Is the emission of electrons by certain
metals when light shines on them
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Energy
Excited Atom
Photon of Red
Light is Emitted
Lower Energy
State Atom
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Light is Emitted. WHY?
• As energy is applied, the atom leaves a lower
energy state (called the ground state) and
reaches a higher energy state (called the excited
state).
• As the atom looses energy, it will return to the
ground state. As it returns to the ground state, a
photon of light is emitted and observed.
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Review:
• Which type of energy on the spectrum has the
greatest energy?
• Which type of energy on the spectrum has the
largest wavelength?
• Which type of VISIBLE energy (ROYGBIV) has
the largest wavelength?
• Which type of energy on the spectrum has the
smallest frequency?
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The End !!!!!!!!!!!!!!!!!!!