To summarize, the electronic configuration of the first eighteen elements follows these rules: the K shell (n=1) can hold a maximum of 2 electrons, the L shell (n=2) can hold a maximum of 8 electrons, and the M shell (n=3) can hold up to 8 electrons. Electrons fill the shells in a stepwise manner, starting with the K shell, then the L shell, and finally the M shell, with a maximum of 8 electrons in the outermost shell.
Detailed Explanation:
1. Maximum Electrons per Shell:
The maximum number of electrons that can be accommodated in a shell is determined by the formula 2n², where ‘n’ is the principal quantum number or shell number (1, 2, 3…).
For the K shell (n=1): 2(1)² = 2 electrons.
For the L shell (n=2): 2(2)² = 8 electrons.
For the M shell (n=3): 2(3)² = 18 electrons.
However, for the first 18 elements, the M shell will not be fully filled (8 electrons).
2. Shell Filling Order:
Electrons are first filled in the K shell, followed by the L shell, and then the M shell.
The outermost shell (in this case, the M shell) can hold a maximum of 8 electrons.