The number of electrons that can fit in each electron shell of an atom is determined by the principal quantum number nnn of that shell, and can be calculated using the formula:
Maximum electrons per shell=2n2\text{Maximum electrons per shell}=2n^2Maximum electrons per shell=2n2
where n=1,2,3,…n=1,2,3,\ldots n=1,2,3,… is the shell number. Electrons per shell:
- 1st shell (K shell, n=1n=1n=1): up to 2 electrons
- 2nd shell (L shell, n=2n=2n=2): up to 8 electrons
- 3rd shell (M shell, n=3n=3n=3): up to 18 electrons
- 4th shell (N shell, n=4n=4n=4): up to 32 electrons
- 5th shell (O shell, n=5n=5n=5): up to 50 electrons
- 6th shell (P shell, n=6n=6n=6): up to 72 electrons
This pattern continues for higher shells as well
. Explanation:
- Each shell contains subshells (s, p, d, f, etc.).
- Each subshell consists of orbitals, and each orbital can hold 2 electrons with opposite spins.
- The number of electrons per subshell is:
- s subshell: 2 electrons
- p subshell: 6 electrons
- d subshell: 10 electrons
- f subshell: 14 electrons
- For example, the first shell has only an s subshell (2 electrons), the second shell has s and p subshells (2 + 6 = 8 electrons), and the third shell has s, p, and d subshells (2 + 6 + 10 = 18 electrons)
Thus, the electron capacity of each shell increases with the shell number, following the 2n22n^22n2 rule, but in actual atoms, electrons fill shells and subshells according to energy levels and quantum rules, so shells may not always be completely filled before electrons occupy the next shell
