modern atomic theory: bohr's planetary model of the atom
DESCRIPTION
Modern Atomic Theory: Bohr's Planetary Model of the AtomTRANSCRIPT
This stuff is really weird…
Mind Map Notes
Modern Atomic Theory
Preamble - Before Atomic
Theory Problems and
Conflicts
Transition
Ideas
I’m tired…
knew that there was a negative particle in the atom but where is it???
Which Experimenter? Review• Model of atom was dense mass
(protons) in center with electrons around it.
• This model had some serious problems.
• Why doesn’t the nucleus fly apart?
• Why aren’t the electrons attracted to the nucleus?
Like charges REPEL!
Opposite charges ATTRACT!Nuclear Model
Mind Map Notes
Modern Atomic Theory
Preamble Before
Atomic Theory
Thom
pson
Disc
over
s
Electro
n bu
t doe
sn’t
know
whe
re it
isRuthe
rford
disc
over
s nuc
leus
and
prot
on
Before Atomic Theory
• Light was considered a wave
• All waves must travel through a “medium” (like water)
• The universe was filled with a substance called “Ether” that light traveled through
BACKGROUND - The Wave Nature of Light
• Wavelength – How far apart the waves are
• Frequency– How fast the waves travel
• Wavelength and Frequency are related• Wavelength and Frequency are
DIRECTLY related to amount of ENERGY in the light.
Light is “Electromagnetic Radiation” MEANS - a form of energy that exhibits wave like characteristics
Wavelength and Frequency
• Not Working very hard
• Long Wavelength
• Low Frequency
Wavelength and Frequency
• Working VERY hard
• Short Wavelength• High Frequency
What does this tell you about the relationship between wavelength, frequency and energy?
Wavelength and Frequency are “INVERSELY PROPORTIONAL”
Energy and Light
Which colors of light have the greatest energy?
Which colors of light have the least energy?
How do you know?
Greatest - Violet, blue, x-rays
Least - Red, orange, infrared, radio waves
Long wavelengths use less power to generate.
Before Atomic Theory
• Light was considered a wave
• All waves must travel through a “medium” (like water)
• The universe was filled with a substance called “Ether” that light traveled through
Photoelectric Effect: Problems & Conflicts
• In the early 1900s an experiment was done that COULD NOT be explained by light being a wave.
• Different colors were shined on to a metal plate
• Electrons would come off the metal plate for ONLY CERTAIN FREQUENCIES OF LIGHT (colors)
If light was a “wave” ANY frequency of light would ALWAYS cause electrons to be released.
Brick Wall Analogy
• Different balls thrown at wall
• Each one with different mass
• All at same speed of 90 mile/hour
• Each ball is like a color or light - each has its own energy
Ping Pong Ball
No effect
Softball
No effect
Super Dense Steel Ball
Dislodges Brick and send it flying
Mind Map Notes
Modern Atomic Theory
Preamble
Thom
pson
Disc
over
s Elec
tron
but d
oesn
’t kn
ow w
here
it is
Ruthe
rford
disc
over
s
nucle
us an
d pr
oton
Light
was
cons
ider
ed a
wave
and
trave
led th
roug
h “E
ther
”Problem
s and Conflic
ts
Photo Electric Effect conflicts
with understanding of light
Differen
t colors
(frequencie
s) of
light c
aused
differen
t responses
New Idea - Einstein and the Photoelectric Effect
• This observation led Einstein to believe that light acted like a particle and a wave
• This is called the “dual nature” of light
Mind Map Notes
Modern Atomic Theory
Preamble
Thom
pson
Disc
over
s Elec
tron
but d
oesn
’t kn
ow w
here
it is
Ruthe
rford
disc
over
s
nucle
us an
d pr
oton
Light
was
cons
ider
ed a
wave
and
trave
led th
roug
h “E
ther
”Problem
s and Conflic
ts
Photo Electric Effect conflicts
with understanding of light
Differen
t colors
(frequencie
s) of
light c
aused
differen
t responses
Tran
sitio
n Id
eas
Einstein says light
has “dual nature”
Plank and the Photoelectric Effect
This was the basis of “Quantum Theory”
Maxwell Plank suggested that because energy was NOT being given off continuously, he suggested that little “packets” of energy called ‘quanta” were being given off.
Line Emission Spectrum Observations
• Experiments were conducted on different elements
• Different elements were observed to produce different colors (or frequencies) when supplied with energy
Identifying Elements with Flame Tests
Na K Li Ba
Energy - 3 Categories - Review• Potential Energy
– Position– In Chemistry - the position of
atoms with respect to each other• Kinetic Energy
– Movement– In Chemistry - heat, molecules
moving• Radiation
– Electromagnetic Spectrum– In Chemisty - radiation and light
Electrons and the Atom
Nucleus
Electron at “Ground State”
e-
Add Energy
e-
electron at “Excited State”
Electron at “Ground State”
e-
Just like a jumper has potential energy at the top of the jump, the electron has stored potential energy in the higher orbit.
Quantum Leap
Electrons disappear from one orbit and reappear at another without visiting the space in between!
Release Energy in the form of colored light
Neils Bohr and the Planetary Model of the Atom
• Bohr hypothesized that electrons could only be at certain energy “levels”
• Electrons could “jump” from lower to higher energy states or higher to lower
• Specific frequencies result in specific colors for each element.
Quantum Levels
• Each energy level is given a number (quantum number)
• When an electron goes from one quantum level to another, it gives off a specific amount of energy that will produce a specific frequency and wavelength (colored light)
If you Think This is Hard to Understand…
A person who wasn’t outraged on first hearing about quantum theory doesn’t understand what had been said…
Neils Bohr
Until it is observed an electron must be regarded as being “at once everywhere and nowhere”
This is “an area of the universe that our brains aren’t wired to understand.”
Dennis Overbye,scientific commentator
James Trefil,
Scientific Author
Things on a small scale behave nothing like things on a large scale.
Mind Map Notes
Modern Atomic Theory
Preamble
Thom
pson
Disc
over
s Elec
tron
but d
oesn
’t kn
ow w
here
it is
Ruthe
rford
disc
over
s
nucle
us an
d pr
oton
Light
was
cons
ider
ed a
wave
and
trave
led th
roug
h “E
ther
”Problem
s and Conflic
ts
Photo Electric Effect conflicts
with understanding of light
Differen
t colors
(frequencie
s) of
light c
aused
differen
t responses
Tran
sitio
n Id
eas
Einstein says light
has “dual nature”
Bohr’s Model of the Atom
(planetary), Electrons at only
certain levelsPlank’s “Quanta”
Line Emission
Spectrum
Showed electrons could only
be at certain energy levels
How am I Supposed to Remember this Stuff?
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
I was riding along in my Rather have a Ford, with the gold foil wrapped plum pudding in the back…(Rutherford)
When I hit a brick wall… (analogy)
Of course at an accident, you always take a photo… (photoelectric effect)
But nothing happened, so it was boring…(Bohr)
However, I did see some colors, which was exciting… (line emission spectrum)
At that point I had a lot of questions… (Q is for Quantum Theory)
And I was uncertain as to what to do… (Heisenberg Uncertainty Principle)
If you turn it sideways you can see the levels…
• Einstein first suspected the fallacy of Ether when he was 15.
• He wrote his first paper on this theory and sent it to his uncle
• In 1881 and 1887 the Michelson Morely experiment proved Ether did not exist.
Einstein! Quit looking out the window! You need to do your math!
Of course Ether exists, you silly boy! All scientist agree!
• Bohr postponed his honeymoon to write his paper
• We consider the “planetary model” to be created by Bohr but actually a Japanese physicist named Hantaro Nagaoka did in 1904 - too bad it was TOTALLY WRONG!