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Name:  Arceli
Status: student
Grade: 9-12
Location:AZ
Country: N/A
Date: 9/12/2005


Question:
How many shells are available for an atom to use up? This depends upon how you want to define "shells". If you mean only the primary quantum number (n) only, and not the sub-shells, usually labeled as (s,p,d,f,g,...), nor the sub-sub-shells caused by electron-electron spin interactions, and sub-sub-sub shells caused by electron-nuclear spin piled on top of all the other sub shells, and other corrections for finite electron mass, and corrections for relativity, then the energy of the shells goes like E = R*[1-1/n^2] for the simplest atom, hydrogen. Then, after all those provisions, the observation of the "excited" electron (let's assume a single electron from the H atom) is smeared out by a number of effects: 1. Doppler broadening -- that is the difference in frequency that occurs as a result of the particular H atom moving toward or away from the detector, 2.Pressure broadening that comes from three sources -- A. that is due to collisions between emitting atoms and the particles surrounding it; Van der Waals broadening that is due to induced broadening of an electronic state resulting from an induced dipole. 3. Stark broadening that results from complex interactions (too messy to address here).


Replies:
I am not intending to "over answer" your question to just throw up a bunch of technicalities in your face to avoid a simple answer, but your inquiry really opens up a lot of very involved effects and it would be intellectually dishonest to sweep them "under the rug". Your question is very basic and deserves a full answer, even though analyzing the effects in detail is quite complicated.

You can find the known energy levels of many elements at the website: http://physics.nist.gov/asd There is a whole field of atomic spectroscopy devoted to the study of the spectra of where the outer electron is in an energy state "close to being" an ion. Those are called Rydberg states and behave "almost" like single electron atoms with a nucleus having a charge of the atomic number, (Z-1). To repeat, your question is very valid, but I don't think there is a "simple" answer. You can also find a summary of the answer to you inquiry in the American Institute of Physics (AIP) Desk Reference under "Atomic Spectroscopy".

Vince Calder


Arceli,

There are 7 shells (energy levels) available. Hvae you ever seen an Aufbau filling diagram?

It looks like this:
7s  7p  7d  7f
6s  6p  6d  6f
5s  5p  5d  5f
4s  4p  4d  4f
3s  3p  3d
2s  2p
1s

So, let's say you wanted to write the electron configuration for Sulphur. From the periodic table, we know sulphur's atomic number is 16--which means it hass 16 electrons and 16 protons. Now, using the table, we're going to write the electron configuration. We start from the bottom left of the table (1s) and then go up on diagonal lines from the right corner to the left.

For example, for S-16 (the number is () is the number of electrons that can go in each orbital): 1s(2)2s(2)2p(6)3s(2)3p(4)

Here's one more example. Fe-26 1s(2)2s(2)2p(6)3s(2)3p(6)4s(2)3d(6)

Using this table, you can easily write the electron configurations for any element! Including the really big ones.

So, if you write out the configuration for the last element on the periodic table, you can...and you'll see the highest number orbital you get to is 7.

Hope this helps.
--Michelle Weinberger



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