Transcript Evidence For The Atomic Structure

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Evidence For The Atomic
Structure
Noadswood Science, 2012
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Sunday, April 3, 2016
Evidence For The Atomic Structure
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To understand the Rutherford scattering experiment
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Plum Pudding
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An early model about the structure of the atom was called the
plum pudding model
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In this model, the atom was imagined to be a sphere of
positive charge with negatively charged electrons dotted
around inside it like plums in a pudding
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The positively charged matter
in the atom was evenly spread
about (pudding)
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The electrons were buried
inside (plums)
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Disproved
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Rutherford, the father of nuclear physics, conducted an
experiment which proved the plum pudding idea was
incorrect
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Rutherford, along with Geiger and Marsden proved the plum
pudding model incorrect with their scattering experiment
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Scattering Experiment
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A beam of alpha particles was aimed at very thin gold foil
and their passage through the foil detected
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Scattering Experiment
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A beam of alpha particles was aimed at very thin gold foil
and their passage through the foil detected
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The alpha particles were expected to pass straight through
the foil, but instead some of the alpha particles emerged
from the foil at different angles, and some even came straight
back
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The positively charged alpha particles were being repelled
and deflected by a tiny concentration of positive charge in
the atom
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As a result of this experiment, the plum pudding model was
replaced by the nuclear model of the atom
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Scattering Experiment
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Scattering Experiment
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Most of the alpha particles passed straight through the metal
foil
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The number of alpha particles deflected per minute
decreased as the angle of deflection increased
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About 1 in 10’000 alpha particles were deflected by more
than 90o
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Rutherford said this was like “firing naval shells at cardboard,
and discovering the occasional shell rebounds”
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Scattering Experiment
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From this experiment Rutherford concluded that there is a
nucleus at the centre of every atom which: -
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Is positively charged because it repels alpha particles
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Is much smaller than the atom as most alpha particles passed
through it
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Is where most of the mass of the atom is located
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The nucleus diameter was found to be about 100’000 times
smaller than the atom
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Scattering Experiment
Thin gold foil
Alpha
particles
Most particles passed
through, but 1/10’000 were
deflected by more than 900
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Atomic Structure
Electron – negative;
mass of 1/2000th
Neutron – neutral;
mass of 1
Proton – positive;
mass of 1