Download History of Atomic Theory Review Notes

History of Atomic Theory
Review of In-Class Research
Tuesday, September
2015
th
15 ,
Ancient Philosophy
 Who: Aristotle, Democritus, Leucippus
 When: More than 2000 years agoears ago
 Where: Greece
 What: Aristotle believed in 4 elements:
Earth, Air, Fire, and Water. Democritus
believed that matter was made of small
particles he named “atomos”.
 Why: Aristotle and Democritus used
observation and inference to explain the
existence of everything.
What did an Atom Look
Like to the Greeks
(Democritus)?
This was Democritus’ atomic model. It was
simply a round sphere with no
electrons, protons, or neutrons.
Democritus created the first atomic model.
His contribution helped people to
understand the idea of an atom, then other
scientists looked further into the science of
the atom and its general makeup.
Dalton’s Particle Theory of Matter
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Who: John Dalton
When: 1808
Where: England
What: Described atoms as tiny
particles that could not be divided.
Thought each element was made
of its own kind of atom.
• Why: Building on the ideas of
Democritus in ancient Greece.
What did an Atom look like to Dalton?
Discovery of Electrons
• Who: J. J. Thomson
• When: 1897
• Where: England
• What: Thomson discovered that
electrons were smaller particles of an
atom and were negatively charged.
• Why: Thomson knew atoms were
neutrally charged, but couldn’t find the
positive particle.
Thomson’s Cathode Ray Tube
Understanding Thomson’s Experiment
What did an Atom look like to
Thomson?
Bunch of negative charged particles
(raisins) in a sphere of positive charge
(plum pudding)
Discovery of Nucleus
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Who: Ernest Rutherford
When: 1911
Where: England
What: Conducted an experiment
that resulted in discovery of atom’s nucleus.
Decided that the atoms were mostly empty
space, but had a dense central core.
• Why: He knew that atoms had positive and
negative particles, but could not decide how
they were arranged.
Rutherford’s Gold Foil Experiment
What did an Atom Look Like
to Rutherford?
Bohr’s Model of the Atom
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Who: Niels Bohr
When: 1913
Where: England
What: Proposed that electrons traveled in
fixed paths around the nucleus. Scientists
still use the Bohr model.
• Why: Bohr was trying to show why each
element emitted its own unique frequency
of energy as electrons jumped orbits.
Bohr’s Model of the Atom
- The Electron
Cloud
Our Current Model
- Bohr said electrons orbit the nucleus
(like the planets around the Sun)
- The electron cloud model says that
we can't know exactly where an
electron is at any given time, but the
electrons are more likely
to be in specific areas.
- The Electron
Cloud
Our Current Model
- Bohr assigned electrons to
different shells
- Using quantum mechanics, the
electron cloud model assigns
electrons to different atomic
orbitals. ** These are not all
spheres
For the quiz/test
• You should know the main scientists and their
experiments/contributions.
• You should be able to draw their models of
the atom and explain differences.