Chemistry Class Notes—Ch 5 Electron Arrangement in Atoms
pg 128-129 atomic model timeline
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Thomson—plum pudding model…electrons embedded in a sphere of positive charge
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Rutherford—(show video)
o conducted gold foil experiments that helped explain atomic structure
o the atom has a very small positively charged nucleus with a larger region called
the electron cloud where the negatively charged electrons are located
o his model did not explain where the electrons are located in the space around
the nucleus (fixed locations, fixed orbits, ???)
o he proposed that electrons move around the nucleus like planets around the sun
o did not explain the chemical properties of the elements
o needed a model that better explained the behavior of electrons
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Bohr—(a student of Rutherford’s) proposed that electrons move in circular orbits at
fixed distances from the nucleus and have specific energies
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De Broglie—proposed that electrons are particles that have wave properties (energy)
o it requires a quantum (fixed amount) of energy for an electron to move from
one energy level to another (like going up steps…it requires a given
amount of energy to move from one step to another)
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Schrodinger—developed the electron cloud model
o developed the quantum mechanical model which determines the likelihood
of finding an electron in various locations around the nucleus (orbitals)
pg 139 electromagnetic radiation spectrum
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light is a form of electromagnetic radiation—a form of energy that exhibits
wave like behavior as it travels through space
examples—x-rays, ultraviolet light, infrared light, microwaves, radar, radio waves
the electromagnetic spectrum is made up of all forms of electromagnetic radiation
all forms of electromagnetic radiation move at a constant speed—3.0 x 108 m/s
(the speed of light—c)
the movement of electromagnetic radiation is a repetitive wave motion (sine wave)
waves are characterized by wavelength, amplitude, and frequency
wavelength is the distance between corresponding point on adjacent waves (pg 138)
(lambda (λ) represents wavelength given in m)
the visible spectrum has wavelengths ranging from 400 nm (violet) to 700 nm (red)
frequency is the number of waves passing a given point in a specific time (second)
(nu (v) represents frequency Hertz (cycles per second))
the wavelength times the frequency is a constant equal to the speed of light
Which color of light has the higher energy, violet or red?
What is the relationship between wavelength and energy of the types of
electromagnetic radiation?
An equation relating wavelength and frequency is…c = λ v
Solve problems pg 140 #14 & 15
Atoms, electrons, and the atomic emission spectrum…
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atoms whose electrons are in the lowest possible energy lever are in the ground state
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atoms whose electrons have absorbed energy and jumped to higher energy levels are
in the excited state
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when the electrons return (or fall back) to their original energy level they release
the energy that was absorbed in the form of electromagnetic radiation…
that is light in increments of photons
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passing the light energy emitted through a prism will produce an identifying lineemission spectrum
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it is not a continuous spectrum of all frequencies of electromagnetic radiation but
specific frequencies related to the energy change of the electrons in a
specific atom
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the atoms of each element have a distinguishing line-emission spectrum which
can be used to identify the element…spectroscopy is used to identify
elements making up the stars and other celestial bodies
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an atomic emission spectrum indicates the wavelengths of light emitted as
electrons fall back to the ground state from an excited state…the
emission spectrum is an identifying property of the atoms
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http://jersey.uoregon.edu/elements/Elements.html
Assign: pg 143 checkpoint
pg 146 #20,21
pg 149-150 #31, 42,45,46,47, 50, 51, 52, 53, 62, 63, 64
http://mutuslab.cs.uwindsor.ca/schurko/molspec/animations.html (photoelectric effect)
http://www.lon-capa.org/~mmp/kap28/PhotoEffect/photo.htm
http://www.colorado.edu/physics/2000/quantumzone/photoelectric.html
http://hyperphysics.phy-astr.gsu.edu/hbase/mod1.html