Question

When does principal series exist in spectra of alkaline metal:?

Answer 1

Answer:

The series of Alkali atoms contain Lithium (Z=3), Sodium(Z=11), Potassium(Z=19), Rubidium(Z=37) and Cesium(Z=55) and their configurations are 1s22s,1s22s22p63s,1s22s22p63s23p64s, 1s22s22p63s23p63d104s24p65s, 1s22s22p63s23p63d104s24p64d105s25p66s

This suggest that an alkali atom consists of one or more closed shell of electron in its ground state and a single valance electron in a new shell in ns orbit.

Now visualizing the two particle system with a lone (valance) electron subjected to Coulomb field of a point charge that is equivalent to proton of the diameter~ 10-15m and is thus the simplest spectra.

The aim is to solve this two-body system exactly to find the wave functions and understand the meaning of the four quantum numbers and .

Keeping in mind the shell model to understand the structure of the alkali spectra and It is the fact that the fine structure and magnetic field splitting are smaller than the gross structure energies by a factor of about Fine structure and the field splitting of the transitions (lines) can be understood after the gross structure of the spectrum.

So far, on the basis of shell model, the atomic states are known.

OR valence electron of sodium is moving in a net field of charge (due to the core of finite size) apparently like a lone (valence) electron in hydrogen atom, moves around the proton (point charge). Therefore it is assumed that the spectra of sodium atom are expected to be analogous to that of the hydrogen as in both the cases, respective valence electron moves in a net field of but with the difference that the field is from the finite size core in former whereas from a point charge (proton) field in the later case.

The closed shell has Zero Total angular momentum and Zero spin angular momentum and designated as 1S0

The valance electron can be excited to various s,p,d,f,…. Orbits those results in doublet terms.