Electronic Configuration of Atom

The distribution of electrons into different orbits of an atom was suggested by Bohr and Bury. Electrons revolve around the nucleus in specific shells or energy levels, which are stable and have definite energy. The shell closest to the nucleus is called the first shell (K-shell), followed by the second shell (L-shell), and so on.

The ordinal number of each shell is denoted by ‘n,’ where shells are labelled as K (n=1), L (n=2), M (n=3), N (n=4), and so forth. The maximum number of electrons each shell can hold is determined by the formula: 2n².

• K-shell (n=1): Maximum of 2 electrons.
• L-shell (n=2): Maximum of 8 electrons.
• M-shell (n=3): Maximum of 18 electrons.
• N-shell (n=4): Maximum of 32 electrons.

As the value of n (ordinal number) increases, the energy level of electrons in that shell also increases. This means that electrons in shells farther from the nucleus have higher energy.

• The electronic configuration of an element describes how electrons are distributed across these shells according to their energy levels and maximum capacity.
• Electrons fill the lower-energy shells (closer to the nucleus) first, before occupying higher-energy shells. This distribution minimizes energy and ensures stability.
• Each electron’s energy depends on the shell it occupies. The K-shell electrons have the lowest energy, while energy increases in subsequent shells (L, M, N, etc.).
• The arrangement of electrons in shells maximizes the overall energy of the electrons in an atom while adhering to the shell capacities.
• The shell-wise electron distribution is fundamental in understanding the properties and reactivity of different elements.

The electronic configuration of an element is shown numerically, using numbers separated by commas. These numbers represent how electrons are distributed in each shell, starting from the lowest energy shell to higher ones.

For example, sodium (Na) has 11 electrons. Its configuration is written as 2, 8, 1:

• K-shell: 2 electrons
• L-shell: 8 electrons
• M-shell: 1 electron

This means the electrons are arranged in shells in order of increasing energy, with the first shell (K) filled first, followed by the next shells.