Simple Electron Configuration Question

[Patriciamsv]

I have read from a few sources that an atom's third energy level can sometimes hold 8 electrons, and other times hold 18.

In atoms which possesses enough electrons to exceed the the third energy level, what exactly is it that determines the amount of electrons this energy level can hold?

 

[Simon Bridge]

The number of electrons in an energy level (the n quantum number) can hold is determined by the relationship between energy and angular momentum, and the Pauli exclusion principle. You have to model it with quantum mechanics.

The formula is $N_e=2n^2$

afaik: the n=3 state may have up to 18 electrons.
Do you have a reference for the 8 electron situation.
http://education.jlab.org/qa/electron_number.html

 

[Patriciamsv]

Thank you for your helpful response. I have read of the 8 electron situation from GCSE and IGCSE textbooks, and as this is a quantum mechanical effect it is probable that it has been simplified for all young students.

 

[Simon Bridge]

I suspect, then, that you will find that the GCSE/IGCSE texts are either referring to something other than the n=3 level, 8 electrons will fill up to the third subshell (=2p). or that there was a typo in the text. It is simply incorrect as you have stated it.

See, for a more complete picture:
http://en.wikipedia.org/wiki/Electron_shell

 

[LudusRex]

The number of electrons that an energy level can hold is determined by the rules of electron configuration. In general, the first energy level can hold a maximum of 2 electrons, the second energy level can hold a maximum of 8 electrons, and the third energy level can hold a maximum of 18 electrons. However, there are exceptions to this rule, such as in transition elements where the third energy level can hold more than 18 electrons. This is due to the fact that these elements have partially filled d orbitals, which can accommodate additional electrons. Other factors that can affect the number of electrons an energy level can hold include the atomic structure and the number of protons in the nucleus. Ultimately, the number of electrons in an energy level is determined by the overall stability of the atom and its electron configuration.