Download Thomson.Rutherford.Bohr.INM.9.10.2012

Today’s Catalyst
1. What is a chemical change?
2. Which of the following substances can NOT be
broken down by a chemical change? Why?
A. ammonia
B. propane
C. carbon
D. water
Today’s Catalyst
3. Sketch a timeline of the atom including what
we have learned so far (Dalton and Thomson).
Include a drawing of the atom, the year of the
discovery, and a description of the atom. (DO
AT THE END OF CLASS TODAY!)
4. Correct the following statement to make it
true… “All atoms of the same element are
identical.”
2
Hmmmmm…..
Wonder what these
mean?? Coming soon!!
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Modern Atomic
Theory
{ Three more dead guys
By the end of the class period
today I will be able to…
Understand Rutherford’s alpha particle
experiment and the discovery of the
atomic nucleus.
Identify Thomson’s Plum Pudding idea
as a model for atomic structure.
Draw a representation of Bohr’s nuclear
atom.
Understand why Bohr’s model is
fundamentally incorrect
Thomson’s Electrons

Who was J.J. Thomson? Thomson
experimented (in 1897) with a cathoderay tube like the one shown on the next
slide. He discovered negatively charged
particles that are now known as
electrons.

Like Plums in Pudding After learning
that atoms contain electrons, Thomson
proposed a new model of the atom.
Thomson thought that electrons were
mixed throughout an atom, like plums in
a pudding.
The Cathode-Ray Tube
Lightning Fast Review
1)
What is an example of one of Dalton’s
postulates?
2) Which of Dalton’s postulates is no longer
considered true? Why?
3) How did Thomson picture the atom?
What was the analogy he used?
Ernest Rutherford
New Zealander
• In 1911 performed
his gold foil
experiment
•
The Gold Foil
Experiment
Observations from gold
foil experiment:
1)
2)
Most of the alpha particles passed
through the gold foil un-deflected
Very few bounced back (great
deflection)
Modern Atomic Theory
Actual
Results
{
Expected
Results
Rutherford’s Conclusion:
1) The nucleus is small,
dense, and has a
positive charge
2) The nucleus is
composed of protons
and neutrons
Summarize the gold foil
experiment. What model
did Rutherford’s
experiment disprove?
Sample Summary
Alpha Particles (2 protons/2 neutrons) were
shot at a piece of gold foil. Part of the
particles were deflected (bounced off), while
others passed straight through. Thereby
convincing Rutherford that the center of an
atom (the nucleus) is positively charged.
 Rutherford’s experiment disproved
Thomson’s plum pudding idea. If the plum
pudding idea were true, all the alpha particles
would have passed straight through.

Niel Bohr
1912
Convinced atom
was small positive
nucleus with
electrons orbiting
around it
• Constructed model of
the hydrogen atom with
quantized energy levels
(electrons can only exist
on certain energy
levels/rings)
Bohr Model
Pros and Cons of the Bohr
Model
Pros:
Con:
+The model gives
us a clear visual
of the atom
+Accurate model
for Hydrogen
-Electrons DO NOT
move around the
nucleus in circular
orbits like planets
orbiting the sun
Rules for drawing Bohr
Models
1) We will be working with neutral atoms, so we can
expect the number of electrons in each element to be
equal to that element’s number of protons!
(#electrons = #protons)
2) Draw each electron energy level with a ring.
3) Electrons fill energy levels in the following way:
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Carbon
Bohr Model
6 Protons
6 Electrons
Nitrogen
Bohr Model
7 protons
7 electrons
Sodium
Bohr Model
? protons
? electrons
Today’s Homework
nd
2
Finish the
Catalyst
Question AND
complete the EXIT
TICKET