So that's it? Atoms really look like little solar systems with
electrons making quantum jumps between special orbits?
Well, not quite. The idea of an electron
actually flying around in little
circles turned out to have lots of problems, and physicists were
eventually forced to discard
that model.
But we just finished talking about how well that worked!
Why do we have to throw the whole thing away?
We're not going to start from scratch. The concept of
"special orbits" was extremely useful, it's just the
orbits themselves that we're not going to use anymore.
Instead, we're going to think about electrons being in
special energy levels. We just use this rule:
Bigger Orbit = Higher
Energy
Oh, that's easy enough. But why bother? Why not just call them orbits?
Well, first of all, some orbits have the same energy as other orbits,
so sometimes changing orbits wouldn't emit radiation.
Also, it turns out that electrons don't really move in little circular orbits.
We can take a little detour to see how the Schrödinger Atom
more accurately depicts what is happening inside atoms.
Actually, thinking about energy levels makes more sense, anyway, because
if the energy goes down the extra energy has to go somewhere, so it
comes out as electromagnetic radiation.
Yeah, and in order for the energy to go up it has to come from
somewhere, so it takes some incoming radiation!
This next applet shows the Bohr model along with a diagram showing
the energy level.
This "energy level" picture of an atom is so useful that
most physicists prefer it over the orbital picture.
Hold on.
Earlier we were saying that when an electron changes its
speed or direction, it gives off electromagnetic radiation.
Now we're saying that when an electron changes its orbit (or "energy level") it gives off
electromagnetic radiation.
Which is it?
You're changing your story on us!
Are you making this up as you go along
or what?
Change in velocity was a classical idea, but the quantum physicists
realized the important part is that the energy of the electron changes,
and electromagnetic radiation makes up the difference.
If the energy goes down, the extra energy appears as a photon.
And for the electron to get more energy, it needs to absorb a photon.
Now let's look at how this theory neatly explains spectral lines...
So that's it? Atoms really look like little solar systems with
electrons making quantum jumps between special orbits?
Well, not quite. The idea of an electron
actually flying around in little
circles turned out to have lots of problems, and physicists were
eventually forced to discard
that model.
But we just finished talking about how well that worked!
Why do we have to throw the whole thing away?
We're not going to start from scratch. The concept of
"special orbits" was extremely useful, it's just the
orbits themselves that we're not going to use anymore.
Instead, we're going to think about electrons being in
special energy levels. We just use this rule:
Oh, that's easy enough. But why bother? Why not just call them orbits?
Well, first of all, some orbits have the same energy as other orbits,
so sometimes changing orbits wouldn't emit radiation.
Also, it turns out that electrons don't really move in little circular orbits.
We can take a little detour to see how the 
Actually, thinking about energy levels makes more sense, anyway, because
if the energy goes down the extra energy has to go somewhere, so it
comes out as electromagnetic radiation.
Yeah, and in order for the energy to go up it has to come from
somewhere, so it takes some incoming radiation!
This next applet shows the Bohr model along with a diagram showing
the energy level.
This "energy level" picture of an atom is so useful that
most physicists prefer it over the orbital picture.
