Why the elements are classified in to K L M N blocks and s p d f sub block?

Answer 1

The answers to both of these questions come from spectroscopy -- the study of how materials absorb or emit particular wavelengths of light.

When the lines in the spectrum of atoms were first connected with the electron structure, scientists did not know whether or not the highest energy lines they were seeing were from the innermost electron shell, or whether there were other shells with more tightly bound electrons. So they arbitrarily chose a letter from near the middle of the alphabet that would not be confused with a letter doing any other job. K was chosen. L, M, N, etc. then followed for the next shells moving outward, and scientists soon discovered that there was no J.

In the spectra of atomic elements, there were fairly obvious "series" of lines with different characteristic appearances, and a pattern to their wavelengths -- lines in a series getting rapidly closer together towards shorter wavelengths.

The characteristic appearances of the lines were described as "sharp", "principal", "diffuse", and "faint". The initials s,p,d,f were taken over to describe the subshells in the electron structure which produced these lines.