Hydrogen Spectrum and Spectral Series
When hydrogen atom is excited, it returns to its normal unexcited (or ground state) state by emitting the energy it had absorbed earlier. This energy is given out by the atom in the form of radiations of different wavelengths as the electron jumps down from a higher to a lower orbit. Transition from different orbits cause different wavelengths, these constitute spectral series which are characteristic of the atom emitting them. When observed through a spectroscope, these radiations are imaged as sharp and straight vertical lines of a single color.
Fig. 8 Emission spectra
The spectral lines arising from the transition of electron forms a spectra series.
 Mainly there are five series and each series is named after itâ€™s discover as Lymen series, Balmer series, Paschen series, Bracket series, and Pfund series.
 According to Bohrâ€™s theory the wavelength of the radiations emitted from hydrogen atom is given by
â‡’
where n_{2} = outer orbit (electron jumps from this orbit), n_{1} = inner orbit (electron falls in this orbit)
Fig. 9
 First line of the series is called first member. For this line wavelength is maximum (Î»_{max}).
 Last line of the series is called series limit. For this line wavelength is minimum (Î»_{min})
 The ratio of first member and series limit can be calculated as .
Table 2: Different spectral series
Spectral series

Transition

Î»_{max}

Î»_{min}


Region

1. Lymen series

n_{2} = 2, 3, 4, â€¦, âˆž
n_{1 }= 1




Ultraviolet region

2. Balmer series

n_{2} = 3, 4, 5, â€¦, âˆž
n_{1} = 2




Visible region

3. Paschen series

n_{2} = 4, 5, 6, â€¦, âˆž
n_{1} = 3




Infrared region

4. Bracket series

n_{2} = 5, 6, 7, â€¦, âˆž
n_{1} = 4




Infrared region

5. Pfund series

n_{2} = 6, 7, 8, â€¦, âˆž
n_{1} = 5




Infrared region
