Download 5.3- Physics and the Quantum Mechanical Model

Section 5.3
5.3
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Neon advertising signs are
formed from glass tubes
bent in various shapes. An
electric current passing
through the gas in each
glass tube makes the gas
glow with its own
characteristic color. You will
learn why each gas glows
with a specific color of light.
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Electrons and light both exhibit particle and
wave properties at the same time!
 The “particle” of light is known as a photon
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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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The wavelength and frequency of light are
inversely proportional to each other.
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The amplitude of a wave is the wave’s height
from zero to the crest.
The wavelength, represented by  (the Greek
letter lambda), is the distance between the
crests.
The frequency, represented by  (the Greek
letter nu), is the number of wave cycles to pass a
given point per unit of time.
 The SI unit of cycles per second is called a hertz (Hz).
 1 Hz = 1/second
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This equation means:
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Speed of light = wavelength in meters x frequency in Hertz
If you are given wavelength in nanometers you will need
to convert:
 1 m = 1 x 109 nm
 c = 2.998 x 108 m/s
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A prism separates light into the colors it contains.
When white light passes through a prism, it produces a
rainbow of colors.

The rainbow is called a spectrum
▪ Unlike white light, light from elements produces only a
few colored lines instead of a full rainbow: called atomic
emission spectrum
▪ http://jersey.uoregon.edu/vlab/elements/Elements.html
Atomic emission spectrum- the discrete lines
formed when atoms absorb energy, forcing
electrons into higher energy levels and then lose
energy by emitting light as the electrons fall to
lower energy levels
 The light is made up of only a few specific
frequencies, depending on the element
 Each frequency is a different color
 The light is emitted as electrons fall from one
energy level to another, like from n=4 to n=1
 They are like atomic fingerprints- every element is
unique
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When the electron has its
lowest possible
energy level , 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. (not the orbital
predicted by aufbau chart)
A quantum of energy in the form of light is
emitted when the electron drops back to a
lower energy level.
 This energy is directly proportional to frequency,
which determines the light’s color.
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Light emitted by an electron moving from a
higher to lower energy level has a frequency
directly proportional to the energy change of
the electron
Equation describing energy change of the
electron
 E = h x ν (h = 6.626 x 10-34J*s)
 So different energy level drops result in different
frequencies (and colors) of light
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The fact that electrons behave as waves leads
to some odd observations, like:
Heisenberg’s uncertainty principle
 it is impossible to know exactly both the velocity
and the position of a particle at the same time.
 This limitation is critical in dealing with small
particles such as electrons.
 This limitation does not matter for ordinary-sized
object such as cars or airplanes.

When photons hit metals, they can result in the
ejection of electrons- This is the photoelectric effect
 We use this property to create electron
microscopes, which allow for clearer images since
electrons have smaller wavelengths than light
▪ http://www.teachersdomain.org/resources/phy03/sci/ph
ys/fund/quantum/index.html
▪ http://www.teachersdomain.org/resources/phy03/sci/ph
ys/matter/quantumcafe/index.html - Quantum Cafe