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Electron probability

Posted by Kelly Phariss
Grade level: 10-12
School: Hill City High
City: Hill City State/Province: S.D.
Country: America
Area of science: Chemistry


Explain what is meant by the probability of finding an electron at a point in space.

One of the biggest discoveries in the history of science was that when you start to look at things that are really small, the laws of physics that we know and love start to break down.

For example, it turns out that there is a fundamental limit about how much you can know about a subatomic particle. A physicist named Heisenberg worked out the math of this, and discovered that the more you know about one aspect of a particle (say, its position in space) the less you can know about some other aspect (like its velocity). The closer you look at something, the harder it is to pin down. This idea is known as the Heisenberg Uncertainty Principle.

So let's say you are looking at an electron. The closer you look at it, the fuzzier it gets; you have a harder and harder time knowing exactly where it is. It's almost as if the electron is in many places at the same time, and at any given time you can't be sure just where it is. For any given moment, there is a probability that the electron is in a certain place, but not a certainty. Mathematically, you can describe the position of the electron using what is called the "probability function".

Think of it this way: imagine you put a housefly in a bottle, then take a time exposure of the bottle with a camera. Further, the shortest exposure you can take is one second, although you can take any exposure longer than that. If you take a one minute exposure, you get a blur since the fly was constantly moving. If you take shorter exposures, the image gets clearer, but even the shortest exposure gives you some blur. You never know just where the fly is at any given instant, just sort of a general idea of its location. Well, that's the way the Universe behaves! No matter how short an exposure you can take of an electron, you just cannot see exactly where it is!

One big effect of this is with electrons as they orbit an atom nucleus. Most people think that electrons revolve around the nucleus like planets revolve around the Sun, but that's not really true. Really, the electron only has a probability of being at some point near the nucleus. It can be somewhere in a volume of space, but you can never know just where in that volume it is. That volume is called an orbital, and it is defined by solving the probability function for the electron.

I found some WWW sites with more information on quantum mechanics, which deal with electron probabilities.

  • This site has a list of people that made quantum mechanics possible, including Werner Heisenberg.

  • This is a great page explaining quantum mechanics. It will almost certainly answer any lingering questions you have!

  • ©2008 Phil Plait. All Rights Reserved.

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