# 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 n2 = outer orbit (electron jumps from this orbit), n1 = 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).

For maximum wavelength, if n1 = n, then n2 = n + 1.

So
• Last line of the series is called series limit. For this line wavelength is minimum (Î»min)

For minimum wavelength n2 = âˆž, n1 = n.

So
• 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 n2 = 2, 3, 4, â€¦, âˆž n1 = 1 Ultraviolet region 2. Balmer series n2 = 3, 4, 5, â€¦, âˆž n1 = 2 Visible region 3. Paschen series n2 = 4, 5, 6, â€¦, âˆž n1 = 3 Infrared region 4. Bracket series n2 = 5, 6, 7, â€¦, âˆž n1 = 4 Infrared region 5. Pfund series n2 = 6, 7, 8, â€¦, âˆž n1 = 5 Infrared region