Transcript 2 section 4.1

Question of the Day
1. Why is the energy in
an atom said to be
quantized?
Day 4 1-4
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
The relationship between frequency (n),
wavelength (l), and color to the energy of
light:
n, E : many photon punches
l, E: big gaps between consecutive
photons.
Color: red = low E, violet = high E
Color: red = low E, violet = high E
each color has its own
color = type of light
energy
The Effects of Different Photons:
Microwaves: can’t feel
Infrared: feel with skin, warms or
burns.
Visible light: see with eyes, heats
when absorbed.
Ultraviolet: can’t feel or see, affects
cells – freckles, tan, burn, cataracts.
The Effects of Different Photons:
Ultraviolet: can’t feel or see, affects
cells – freckles, tan, burn, cataracts.
X-rays: can’t feel or see, pass
through body, but absorbed by bones
and dense matter.
Gamma rays: can’t see or feel, affects
cells, causes mutations in cells and
molecules.
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. …
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
Day 3 1-3
DEFINE:
energy level AND atomic orbital
AND Read section 5.1 AND answer
questions 1, 2, 4, and 5 on page 132
2 definitions and 4 questions
Radiant Acrostic
R
A
D
I
A
N
T
Day 5 1-5
1. When do we treat light as a
wave? As a particle?
2. 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 m
a
h
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
.
Homework # 1