Explain emission and absorption spectra. Discuss the general description of line spectra in hydrogen atom .

Explanation

Emission spectrum.
1. It is produced by analysing the radiant energy emitted by an excited substance.
2. It consists of bright lines on dark background.
3. Produced due to the emission of energy. by electrons.
4. Emission spectra contains bright lines on dark background.
Line spectra of Hydrogen - Bohr.s Theory:
In case of hydrogen atom line spectrum is observed and this can be explained by using Bohr.s Theory.
According to Bohr.s postulate when an electronic transition takes place between two stationary states that differ in energy is given by
`DeltaE=E_(f)-E_(i)" "E_(f)`= final orbit energy
`E_(i)`= initial orbit energy
We know that `E_(n)=-R_(H)[(1)/(n^(2))]`
`:.DeltaE=(-RH)/(n_(f^(2)))-[-(RH)/(n_(f^(2)))]`
`:.DeltaE=R_(H)[(1)/(n_(f^(2)))-(1)/(n_(f^(2)))]`
`DeltaE=hv`
`v=(DeltaE)/(h)=(R_(H))/(h)[(1)/(n_(i)^(2))-(1)/(n_(f^(2)))]`
`v=(2.18xx10^(-18))/(6.625xx10^(-34))[(1)/(n_(i)^(2))-(1)/(n_(f)^(2))]`
`=3.29xx10^(15)[(1)/(n_(i^(2)))-(1)/(n_(f^(2)))]sec^(-1)`
In terms of wave numbers
`barv=(v)/(c)=(3.29xx10^(15))/(3xx10^(8))[(1)/(n_(i)^(2))-(1)/(n_(f)^(n))]`
`=1.09677xx10^(-7)[(1)/(n_(i^(2)))-(1)/(n_(f^(2)))]m^(-1)`
In case of absorption spectrum `n_(f)gtn_(i)to` energy is absorbed (+Ve)
In case of emission spectrum `n_(i)gtn_(f)to` energy is emitted (-Ve)
Each spectral line in absorption (or) emission spectrum associated to the particular transition in hydrogen atom
In case of large no.of hydrogen atoms large no.of transitions possible they results in large no.of spectral lines.
The Spectral Lines for Atomic Hydrogen