Ask A Scientist Chemistry Archive

name         Barb
status       educator
grade        4-5
location     MI

Question -   I am creating molecules with my students using pipe 
cleaners and beads.  The electrons are on the pipe cleaners around 
the nucleus.  My question is: How many electrons are on each 
ring?  I do not think that all electrons are on only one ring.  Thanks!
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Barb,

I am not sure what your objectives are in this 
demonstration/project. On the one hand, there is some knowledge to 
be gained by being able to visualize electrons around a nucleus, and 
being able to see how much "empty space" there is within an atom. 
However, there will be issues of scale that will creep into this 
demonstration if one is not very careful. Imagine that the nucleus 
is the size of a penny. If that penny were in the middle of a 
football field, the electrons would be in the "nose-bleed" section 
of a NFL type stadium. Moreover, there is also an issue that putting 
electrons on a wire would strongly suggest that the electrons are 
particles that travel on a set path. We have evidence/proof that 
this is not the case. I would be wary of such misapprehension 
getting into the lesson which will then be corrected (with 
difficulty, since erroneous lessons already learned are harder to 
correct then taking the time to get it right the first time) at the 
upper levels.

However, if you think that there is something of value in going 
through this exercise, and you can make sure that your students do 
not misinterpret the lesson, then I would suggest that you look at a 
periodic table. The first two columns from the left (IA and IIA) 
represent atoms that have electrons in the s-orbital (two electrons 
per orbital), the last six columns represent atoms that have 
electrons in the p-orbital (3 total orbitals, two electrons per 
orbital, total of six electrons). As you go down the column the 
orbital "size" increases. Thus, a H atom would have one electron in 
the 1s orbital, the He (think of it as being above Be) would have 2 
electrons in the 1s orbital. The Li atom would have all the 
electrons of He, plus 1 more in a larger orbital, the 2s. And so on.

Greg (Roberto Gregorius)
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