State the difference between a shell and a subshell?

The electron configuration of an element describes how electrons are distributed in its atomic orbitals. Electron configurations of atoms follow a standard notation in which all electron-containing atomic subshells (with the number of electrons they hold written in superscript) are placed in a sequence.

Shells

The maximum number of electrons that can be accommodated in a shell is based on the principal quantum number (n). It is represented by the formula 2n2, where ‘n’ is the shell number. The shells, values of n, and the total number of electrons that can be accommodated are tabulated below.

Shell and ‘n’ value Max. Electrons in the Electron Configuration
K shell, n=1 2*12 = 2
L shell, n=2 2*22 = 8
M shell, n=3 2*32 = 18
N shell, n=4 2*42 = 32

Subshells

  • The subshells into which electrons are distributed are based on the azimithual quantum number (denoted by ‘l’).
  • This quantum number is dependent on the value of the principal quantum number, n. Therefore, when n has a value of 4, four different subshells are possible.
  • When n=4. The subshells correspond to l=0, l=1, l=2, and l=3 and are named the s, p, d, and f subshells respectively.
  • The maximum number of electrons that can be accommodated by a subshell is given by the formula 2*(2l + 1).
  • Therefore, the s, p, d, and f subshells can accommodate a maximum of 2, 6, 10, and 14 electrons respectively.

All the possible subshells for values of n up to 4 are tabulated below.

Principle Quantum Number Value Value of Azimuthal Quantum Number Resulting Subshell in the Electron Configuration
n=1 l=0 1s
n=2 l=0 2s
l=1 2p
n=3 l=0 3s
l=1 3p
l=2 3d
n=4 l=0 4s
l=1 4p
l=2 4d
l=3 4f

Thus, it can be understood that the 1p, 2d, and 3f orbitals do not exist because the value of the azimuthal quantum number is always less than that of the principal quantum number.

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