Question

Explain Bohr-Bury scheme.

Answer 1

Bohr-Bury scheme:

1. The distribution of electrons in different shells is known as electronic configuration.
2. Each shell has a limited capacity to hold electrons and each electron tries to occupy a shell with a lower energy value first and then occupies the shell with higher energy.
3. According to the Bohr Bury scheme, a system is stable when it has less energy.
4. Thus, the electrons first occupy the first shell i.e. K which has the lowest energy then go to the second shell i.e. L, then M, N, and so on.
5. The first shell K shell accommodates 2 electrons, the second shell L shell accommodates 8 electrons, the third shell M shell accommodates 18 electrons and the fourth shell N shell accommodates 32 electrons.
6. The scheme also states that the outermost shell cannot hold more than 8 electrons.

Example:

1. Consider a Calcium $\mathbf{\left(}\mathbf{Ca}\mathbf{\right)}$ atom. The total number of electrons in the Calcium atom is 20.
2. Starting from the nucleus, the first shell i.e. K shell holds 2 electrons, and the second shell i.e. L shell holds 8 electrons. Thus, 10 electrons are filled.
3. Now, the third shell i.e. M shell is expected to hold the remaining 10 electrons.
4. But according to Bohr Bury scheme, the outermost shell cannot hold more than 8 electrons.
5. Thus, the M shell holds 8 electrons and the remaining 2 electrons go into the fourth shell i.e. N shell.
6. Thus, the electronic configuration is (2,8,8,2).