The number of shells an atom can have is determined by the principal quantum number (n) in the electron configuration. The principal quantum number represents the energy level or shell in which the electron resides.
According to the Bohr model and the quantum mechanical model of the atom, the principal quantum number can have any positive integer value starting from 1. Each value of n corresponds to a different energy level or shell.
The maximum number of electrons that can be accommodated in a particular shell can be calculated using the formula 2n², where n is the principal quantum number. For example:
- The first shell (n=1) can accommodate a maximum of 2 electrons (2 x 1² = 2).
- The second shell (n=2) can accommodate a maximum of 8 electrons (2 x 2² = 8).
- The third shell (n=3) can accommodate a maximum of 18 electrons (2 x 3² = 18).
- And so on.
However, it's important to note that as the atomic number increases, the energy levels can overlap and become more complex due to the influence of other factors such as electron-electron repulsion and orbital hybridization. Therefore, the actual electron distribution and arrangement in an atom can be more complicated and may deviate from a simple model based solely on the principal quantum number.