The electrons in atoms occupy a range of different orbitals. Each orbital is characterized by three quantum numbers, each of which has certain allowed values.
- n, the principal quantum number, specifies orbital energy.
Orbitals of the same energy are said to be in the same shell. Allowed values for n are 1, 2,3.…
- l, the angular momentum (subshell) quantum number specifies orbital shape and has allowed values from 0 to n - l.
Orbitals having the same value of n and l are said to be in the same subshell.
Because the number of subshells depends on n, shells with larger n have more subshells.
Subshells are usually designated by a letter:- l = 0 is the s-subshell
- l = 1 is the p-subshell
- l = 2 is the d-subshell
- l = 3 is the f-subshell.
- ml, the magnetic quantum number specifies orbital orientation.
The allowed values depend on the value of the subshell quantum number and are from -l to 0 to +l.
Thus subshells having different values of l have different numbers of orbitals.
A fourth quantum number,
ms (the electron spin quantum number) specifies the spin of the electron in the orbital.
Allowed values +1/2 and -1/2.
Electron configurations, such as 1
s2 for He, show occupied subshells on an atom.
- The first number is n, the principal quantum number for the shell where the subshell is found.
- The letter specifies the subshell and thus the value of l.
- The superscript indicates the number of electrons in that subshell.