Bohr's Atom
To explain the spectral line
puzzle, Bohr came up with a radical
model of the atom which had electrons orbiting around a nucleus.
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That doesn't sound so
radical.
We've already seen how electrons
can orbit around a positively charged nucleus.
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Yes, but in order to explain the "signature colors," Bohr
came up with an extraordinary rule the electrons had to follow:
Electrons can only be in "special"
orbits.
All other orbits just were not possible. They could "jump"
between these special orbits, however, and when they jumped they would
wiggle a little bit...
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And that would cause radiation!
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To see this happening, try clicking on different orbits in the model
of an atom
below.
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Hey, when I click on a smaller orbit, a little colored squiggle
goes shooting out, but when I click on a bigger orbit, a squiggle comes
in and kind of "bumps" the electron up.
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Those squiggles are little bursts of light (electromagnetic energy).
We
call them photons.
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But when we played with the orbits earlier, we saw that just about
any orbit and any speed is possible. It doesn't make sense that
only some orbits would be "allowed."
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Now you can see why the Bohr model was considered so radical! It
said that energy could only change in little jumps. These are called
quanta and that's why this kind of physics is called Quantum
Mechanics.
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Is that where the term "quantum leap" comes from?
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Yup. Ironically, everyday use of the term has come to mean a
big jump,
but physicists use it to mean a jump between allowable orbits, which is
usually very, very tiny. The important part is that these jumps
cannot be
broken down into smaller steps. For an electron on the move it's all or
nothing.
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