Ch. 13: Electrons and Quantum Mechanics

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Ch. 13 Electrons and Quantum Mechanics
Cartoon courtesy of NearingZero.net
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Atomic Theory Review (Ch. 5)
400 BC Democritus
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Spectroscopic analysis of the visible spectrum
produces all of the colors in a continuous
spectrum
Visible Light R O Y G B I V e r e r L n i d a l e
u d o n l e e i l g o n g e e w o t
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Types of electromagnetic radiation
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Spectroscopic analysis of the hydrogen atomic
emission spectrum
produces a bright line spectrum
similar to a bar code or fingerprint.
Each element has its own unique bright line
spectrum
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The Bohr Model of the Atom
I pictured electrons orbiting the nucleus much
like planets orbiting the sun.
I could predict the wavelength of bright line
spectra using laws of planetary motion.
Unfortunately I couldnt make accurate
predictions when there was more than 1 e-.
Neils Bohr
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The Bohr Model of the Atom
I could predict the bright line spectra for an
element with only 1 e- like hydrogen.
Neils Bohr
H
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Turn to the last question on Day 15 notes
5. The Bohr model, although historically
important, was limited in its ability to explain
the behavior of more complex elements and ions.
To which of the following atoms or ions would
you expect the Bohr model to apply? (circle your
choices) Be, He, K,
Li2 Explain your reasoning
He means 1 e- is removed from neutral helium.
I could predict the bright line spectra for an
element with only 1 e- like hydrogen.
I could not predict beryllium because it has 4 e-.
I can also predict ions if they only have 1 e-.
neutral
H
Neils Bohr
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Turn to the last question on Day 15 notes
5. The Bohr model, although historically
important, was limited in its ability to explain
the behavior of more complex elements and ions.
To which of the following atoms or ions would
you expect the Bohr model to apply? (circle your
choices) Be, He, K,
Li2 Explain your reasoning
H
He
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Turn to the last question on Day 15 notes
5. The Bohr model, although historically
important, was limited in its ability to explain
the behavior of more complex elements and ions.
To which of the following atoms or ions would
you expect the Bohr model to apply? (circle your
choices) Be, He, K,
Li2 Explain your reasoning
Li2 means 2 e- are removed from neutral lithium.
I could not predict potassium because it has 19
e-.
H
Neils Bohr
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Turn to the last question on Day 15 notes
5. The Bohr model, although historically
important, was limited in its ability to explain
the behavior of more complex elements and ions.
To which of the following atoms or ions would
you expect the Bohr model to apply? (circle your
choices) Be, He, K,
Li2 Explain your reasoning
H
Li2
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Explain your reasoning
I can only predict bright line spectra for
elements or ions with one electron
Li2
He
Neils Bohr
H
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The Bohr Model of the Atom
I thought e-s follows set paths or orbits.
But I was wrong! They dont have a set path.
Theyre more like bees around a hive.
Neils Bohr
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Electron Energy Level (Shell)
Electrons are shown in energy levels because we
see bright lines from electrons that have been in
excited states.
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Electron Energy Level (Shell)
Principle Energy Levels are symbolized by n, it
denotes the probable distance of the electron
from the nucleus.
Number of electrons that can fit in an energy
level
2n2
Level 1 n 1 2(12) 2 e-
Level 2 n 2 2(22) 8 e-
Level 3 n 3 2(32) 18 e-
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Excited State Adding energy causes the e- to
move into higher energy levels.
e- Transitions
Ground State e- in lowest energy levels.
e- move from ground state to excited state
n 4 ? 2 (red light)
ENERGY!
n 5 ? 2 (green light)
n 6 ? 2 (blue light)
n 7 ? 2 (violet light)
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Absorption spectrum
produces a dark line spectrum
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Atomic absorption and emission spectra
Colors are related to wavelengths of light and
match location on continuous spectrum.
Energy emitted as colors of light (bright lines)
e- move from higher ? lower levels
Energy absorbed as (dark lines)
e- move from lower ? higher levels
The dark lines show where the energy is
absorbed by the electrons.
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Electron transitionsinvolve jumps of definite
amounts ofenergy.
Web link
This produces bands of light with
definite wavelengths.
Infrared Light IR
Visible Light ROYGBIV
Transitions end at n 3 or higher
Transitions end at n 2
U.V.
Ultraviolet light
Transitions end at n 1
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infrared
I.R.
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So how do electrons move and exactly where are
they located?
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Heisenberg Uncertainty Principle
One cannot simultaneously determine both the
position and momentum of an electron.
You can find out where the electron is, but not
where it is going.
OR
You can find out where the electron is going, but
not where it is!
Werner Heisenberg
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Wave-Particle Duality
JJ Thomson won the Nobel prize for describing the
electron as a particle.
His son, George Thomson won the Nobel prize for
describing the wave-like nature of the electron.
The electron is a particle!
The electron is an energy wave!
Who is correct?
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Wave-Particle Duality
Bright line spectra showed that light behaves
like waves and not particles.
Ripple tank link
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Wave-Particle Duality
The photoelectric effect showed that light can
behave like particles not waves.
Photoelectric effect link
Java applet link
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The Wave-like Electron
The electron propagates through space as an
energy wave. To understand the atom, one must
understand the behavior of electromagnetic waves.
Louis deBroglie showed mathematically how all
particles have both a wave and a particle nature.
Louis deBroglie
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Wave-Particle Duality
JJ Thomson won the Nobel prize for describing the
electron as a particle.
His son, George Thomson won the Nobel prize for
describing the wave-like nature of the electron.
The electron is a particle!
The electron is an energy wave!
It turns out they were both correct. We now
believe that the electron can behave as both a
wave and a particle.
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Quantum MechanicalModel of the Atom
Mathematical laws can identify the regions
outside of the nucleus where electrons are most
likely to be found.
These laws are beyond the scope of this class
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Schrodinger Wave Equation
Equation for the probability of a single electron
being found along a single axis (x-axis)
Erwin Schrodinger
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Types of electromagnetic radiation
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Parts of a wave
Crest or Peak
Crest or Peak
Valley or Trough
Valley or Trough
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Electromagnetic radiation propagates through
space as a wave moving at the speed of light.
c ??
C speed of light, a constant (3.00 x 108 m/s)
? frequency, in units of hertz (Hz, 1/s, or
sec-1)
? wavelength, in meters (m)
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Wave Equation
c ??
?
?
c

?
c

?
?
?
?
?
Solved for frequency (?)
Solved for wavelength (?)
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The energy (E ) of electromagnetic radiation is
directly proportional to the frequency (?) of the
radiation.
E h?
E Energy, in units of Joules (J) or (kgm2/s2)
h Plancks constant (6.626 x 10-34 Js)
Energy associated with each change in frequency
of light.
? frequency, in units of hertz (hz, sec-1)
E h ?
Since
Then
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c ??
E h?
Solve for wavelength
Solve for frequency
E
c
?
?


?
h
h 6.626 x 10-34 Js
c 3.00 x 108 m/s
3.00 x 108
6.626 x 10-34
Equations Electron Transition E n l Energy Units (Joules) Frequency (n) Units (s-1) Wavelength (l) Units meters (m)
n 6 ? n 5 2.66 x 10-20
n 6 ? n 4 7.57 x 10-20
?

?
3.00 x 108
2.66 x 10-20
4.01 x 1013
(6.626 x 10-34)
?
?
4.01 x 1013 Hz
Show work on the next 2 problems then only
answers on the rest.