The Pauli Exclusion principle states

in an atom or molecule, no two electrons can have the same four electronic quantum numbers. As an orbital can contain a maximum of only two electrons, the two electrons must have opposing spins.

So how can some electron shells have up to 6 electrons or more? Take the electron configuration of Magnesium. The 2p shell holds 6 electrons. How is this possible? Can you have multiple orbitals in a single electron shell?

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – David Z
    Aug 16, 2016 at 14:56

1 Answer 1


A "shell" is the term for all states with the same principal quantum number $n$, but in each shell there are also possible different values for the angular momentum quantum number $0\leq \ell \leq n$, the magnetic quantum number $-\ell \leq m_\ell \leq \ell$ and the spin quantum number $m_s\in\{-1/2,1/2\}$.

So for $n>1$, 6 electrons in a shell do not violate the Pauli exclusion principle.

  • 1
    $\begingroup$ Note that the OP seems to be using "shell" to mean definite $n$ and $\ell$, since they talk about the "2p shell". (I think most sources would call this a "subshell" instead.) Your logic is still fine for any subshell with $\ell \neq 0$, though. $\endgroup$ Aug 15, 2016 at 19:40
  • $\begingroup$ this is not an exact answer to the question. How did you got 17 upvotes for that ? $\endgroup$
    – user46925
    Aug 17, 2016 at 8:21

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