Transcript
10-102 Spectral Lines
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410 Excited States
Electrons occupying the energy shells in an atom take the form of a cloud
surrounding the much smaller nucleus.
Since only two electrons can fit into each of the energy shells, it is interesting to
look at the characteristics of these different shells or energy states.
These states are defined first by a primary quantum number called “n” and also
by a secondary quantum number called “l”.
And for each state, the electron has a different energy, which results from the
shape of the electron cloud.
For n=1, called the ground state, the shape is a symmetric cloud…the same in all
directions.
For n=2, the shape can take on two forms depending on the value of “l”
…although both shapes have the same energy…
One shape is a double spherical cloud – one sphere inside the other.
While the other shape for n=2 is in the shape of a dumbbell.
For other values of n and l, the shapes can be pretty strange…
Like this torus PLUS dumbbell shape.
From 5-415 Spectral Lines
An electron in the lowest energy shell in an atom can be struck by and absorb
the energy of a photon giving it enough energy to jump to the next energy shell.
And the reverse process allows the electron to jump back down into the lowest
energy shell and emit a photon.
The color of the photon depends on the energy difference between the two
shells.
This explains the spectral lines that identify an element. Since white light
contains all the colors in the spectrum, when we shine white light on a sample of
an element under the right conditions, The atoms absorb all of the photons that
allow their electrons to jump to other energy shells.
SO the absorption spectrum is all the colors in white light minus those that match
the difference in energy shells within the atom.
And when those electrons spontaneously jump back down to the lowest energy
levels, that emission spectrum contains only those lines that match the difference
in energy shells within the atom.
Hydrogen Spectra
Here is a piece of the spectra from hydrogen. The primary quantum number n is
shown on the right alongside the line representing that energy level.
When an electron jumps from the n=3 shell to the n=2 shell, red light is emitted
When an electron jumps from the n=4 shell to the n=2 shell, aqua light is emitted
When an electron jumps from the n=5 shell to the n=2 shell, blue light is emitted
When an electron jumps from the n=6 shell to the n=2 shell, violet light is emitted
When an electron jumps from the n=7 shell to the n=2 shell, ultraviolet light is
emitted
No jumps to n=1 are shown because they are all in the deep ultra-violet.