Model The Bohr Model of the Atom (or Modified Solar System Model): That model of the atom which succeeded the Rutherford Model of the Atom when it was unable to account for the discrete spectrum of light emitted by atoms. The Bohr Model was a planetary model, but allowed only certain discrete possible orbits. Definition Discrete: Separate or individually distinct, consisting of distinct parts or discontinuous elements. Used here to mean the opposite of "continuous" or smoothly varying.

In the animation we show a much simplified Bohr Model of the atom with only three possible orbits (the actual Bohr Model has many, many such orbits.) In the Bohr Model, the larger the orbit, the greater the amount of energy the electron has as it moves in that orbit. In the atom shown, there are only three discrete possible orbits and three discrete possible electron energies to go with them. When the animation begins, the electron will be in the lowest energy orbit and would remain there forever if the electron were not given more energy by some mechanism.

You can "excite" the atom by clicking on the button labeled "Bump Electron Up." Exciting the atom means giving the electron some extra energy. There are two common ways that this can happen. You can bump the atom with an electron that strikes the atom, or you can bump the atom with a photon (light) that is absorbed by the electron in the atom. So, for this animation, imagine that when you click on "Bump the Electron," you are giving the atom's electron more energy.

When you bump the electron, it moves to an orbit with higher energy. Which orbit it chooses depends on how much energy the electron has gained. Try it several times; it randomly does one or the other. If you watch the excited atom for a few moments, it will spontaneously "relax," meaning that the electron will jump down to a lower available orbit. This is also a random choice on the part of the atom. (You can also force the electron to jump down if you wish by clicking on the "Jump Electron Down" button.) When the electron jumps down, it must unload its extra energy which it does by creating and emitting a photon. In this atom there are only three possible ways the electron can jump down and they correspond to three different possible colors of photon. Thus, this atom has a discrete spectrum of exactly three colors. Bump the electron several times until you can see where those three colors are coming from.

Click here to begin the animation.

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