Write the electronic configuration of an element X whose atomic number is 12.

Explanation

Atomic number of the element X is 12 which means that one atom of X has 12 electrons. First of all th electrons will go to K shell which can take a maximum of 2 electrons. Thus, the first 2 electrons will occupy K shell and we write K for it. After filling the K shell, the electrons will go to shell. Now, L shell can take a maximum of 8 electrons for which we write L. In this way `2 + 8=10` electrons have been accomodated, and we are left with 2 more electrons. The remaining 2 electrons go to M shell and we write `underset(2)(M)` for it. Writing all the electron shells together, the electronic configuration of the element X becomes :
`underset(" 2, 8, 2")(" K L M")`
Please not that it is not necessary to write the shell K, L and M, etc., while writing the electronic configurations of the elements. For example, the electronic configuration of the element X of atomic number 12 can by simple written as 2,8, 2. It is, however, better to indicate their shells also. Another point to be noted is that we have given so many details in the solution of this problem just to make you understand the things cleary. There is no need to write so many details in the exam. The arrangement of electrons in the atom of element X has been shown in Figure 23.