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Q & A: atomic pictures

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Most recent answer: 10/22/2007
Q:
In my science book it wanted me to draw a picture of an atom with the nuetrons and protons gathered in a middle circle and the electrons on circles around it. But it never specified how many rings to make or how many electrons to put on each ring. Sometimes they had four and other times they had six. They were always paired. Is there any specific way to do this? Thanks
- Anonymous (age 14)
Texas
A:
Dear trouble:

Yes, there are some definite rules about this, but first we should give a warning. These pictures are just a way of suggesting some information about the atoms. The atoms themselves are not put together in anything like the way the picture suggests, or even any way that can be pictured at all. We have some other answers discussing a little bit of these quantum mysteries.

Of course, the total number of electrons in an atom will be the same as the number of protons in the nucleus, so that the atom is electrically neutral.

The rings for the electrons can be used to suggest how many electrons there are with different amounts of energy. The inner rings represent electrons with low energy, tightly stuck in the atom. I don't know what type of pictures your book favors, but they may also use separate rings to represent electrons which are in different types of states around the nucleus, even when those states have almost the same energy.

The innermost ring can have one or two electrons in it. If that fills up, the next batch can have up to eight electrons in it. Depending on the taste of the illustrator, those may be shown as one ring of two and one of six, or as one ring of eight, since six of those states have a different 'shape' than the other two.

I'm not sure how far up you need to go, but the ring picture starts to get messy if you go much farther.

There's reason for the electrons being shown in pairs. There can be at most one electron in any state. That's why they can't all pile into the low-energy states. However, each state is determined not just by how the electron is distributed in space but also by an internal property called 'spin'. You can put two electrons in the same spatial state so long as they have opposite spin. That's where the pairs come from.

Mike W.

(published on 10/22/2007)

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