Question of the Day
1. Why is the energy
in an atom said to be
quantized (think
Bohr)?
Day 6 1-8
REVIEW
If a light wave has a
15
frequency (ν) of 3.0 * 10
Hz, what is its
wavelength?
1.0 *
-7
10 m
2. Who demonstrated photons
can move electrons?
Compton
Neils Bohr
Tried to explain why each
element has its own
unique (bright) line
spectrum. He studied H.
Using previous discoveries- Bohr
hypothesized that an atom’s electrons are
located in specific energy levels. Each
energy level, aka orbit or shell is a set
distance from the atom’s nucleus. …
Atomic Emission Spectra
Neils Bohr
… Each energy level, aka
orbit or shell. Is a set
distance from the atom’s
nucleus. …
… Electrons jump or fall from one
energy level to another, while
simultaneously gaining or losing energy.
Electrons are not permitted to stop
between energy levels.
Bohr’s Hypothesis
• In the line spectrum of an atom,
Bohr saw specific colors.
• Each specific color has a specific
energy.
• That specific amount of energy is
related to a specific distance from
the nucleus.
Ground vs. Excited States:
An atom is in the ground state when
its electrons fill the lowest possible
energy levels that are closest to the
nucleus. This is when the atom is
most stable.
An electron can gain energy and
jump to a higher energy level. The
electron must absorb an exact
amount …
Ground vs. Excited States:
An electron can gain energy and
jump to a higher energy level. The
electron must absorb an exact
amount … of energy to make a jump
to a specific energy level. The energy
that the electron gains comes from a
photon.
When an atom’s electrons are in higher
energy levels, the atom is in an
excited state and is less stable.
The atom prefers to be stable, so the
electrons fall into lower energy levels
that are not full. As the electrons fall,
energy is released in the form of visible
or invisible light.
atoms prefer…
• to be stable!
• to have low energy!
• to be in their ground state!
Increases away from the nucleus
Radiant Acrostic
R
A
D
I
A
N
T
Day 1 1-9
1. How did Arthur Compton
demonstrate that light can
act as a particle?
Review-Style
If a light wave has a
15
frequency (ν) of 3.0 * 10
Hz, what is its energy?
2.0 *
-18
10 J
Quantum Mechanics
What happens when there is
more than 1 electron?
Mr. Bohr was
concerned with
calculating and
predicting the line
spectra of
elements.
Quantum Mechanics
What happens when there is
more than 1 electron?
Mr. Bohr was concerned with
calculating and predicting the line
spectra of elements. He wondered how
electrons move and where they can be
found in atoms. Bohr’s ideas worked
well for hydrogen with 1 electron. …
Quantum Mechanics
Bohr’s ideas worked well for hydrogen
with 1 electron. … He predicted the
infrared and ultraviolet bands of
hydrogen’s emission spectrum. The
equations he used came from Classical
Mechanics, a branch of physics that
describes the movements and
interactions that are
large enough to see.
But…
Alas.. Bohr could
not predict the
bright-line spectra.
The laws of Classical
Mechanics just don’t
cut it for atoms and
electrons.
Electrons are tricky… they and
other subatomic particles like them
have their own code of conduct…
They behave differently than
anything you may be able to see
with your eyes or with any other
object. New ideas needed to be
looked into, and these new ideas
became known as Quantum
Mechanics.
Louis de Broglie
One of the first to
think that electrons
possess wave
properties. He
reasoned that since waves can
act as particles do (taken from
Planck’s idea about light), then
particles might behave as waves
do.
For tiny subatomic particles…
Wave properties are
important. As the
size of the moving
object decreases, its
wavelength
increases. The
wavelength for a tiny
electron can be as
large as an entire
atom.
So how does an electron move in an atom?
Bohr (and maybe you too…)
thought that they moved in
circular or spherical orbits.
With de Broglie’s matter-wave
idea, now we theorize that
electrons vibrate around the
nucleus in a
.
PRELAB
How is an electron able to change
energy levels?
Day 2 1-10
LAB
NO ATB today. Sit with your
partner(s) for lab and get out
your lab. Wait for instructions.
Day 4 1-14
#4
ΔE = hc/λ
ΔE = change in energy
h = Plank’s constant = 6.63 * 10-34 Js
c = speed of light = 3 * 108 m/s
λ = wavelength (in meters)
E=
(6.63 x 10-34 J s )(3.00 x 108 m/s)
649 x 10-9 m
3.06 x 10-19 J
=
#s 1-4 and 7 –
Due tomorrow
(Tuesday 1-15)
#5
1
1
n2final - n2initial
#6
LAB
The Elusive Electron Evades
Subatomic State Trooper!
Werner Heisenberg
In 1927, he proposed
the Uncertainty
Principle
This states that it is impossible to
know both the speed and location
of an electron at the same time.
Why is it so hard to pinpoint the electron?
To determine the speed and the
location of an object, you must be
able to SEE the object… light is
bounced off the object when you
see it.
Light is made up of quanta or
photons.
When photons hit a speeding car,
the car is unaffected. But when a
photon hits a speeding electron,
the electron will move or change
direction. So, if a photon hits an
electron and the light bounces off
it into your eyes, you will see
where the electron was, but you
won’t know how fast it was going
at the time.
Heisenberg
Explain the Heisenberg
Uncertainty Principle.
It is impossible to know both the
speed and location of an electron
at the same time.
What, am I
speeding?
Homework # 1
day 3 12-15
Quantum Theory
Quanta’s Ability:
Light energy hits the electrons in
metal- the light must be powerful
enough.
Electrons in the metal absorb the
energy.
The electrons become excited,
and they jump out of the metal.
Quantum Theory
The electrons become excited,
and they jump out of the metal.
The electrons fall down again, and
create a spark or current.
Examples: The luster of a shiny
metal, Photoelectric cells (solar
power)