Question

Explain different types of spectral series in a hydrogen atom.

Answer 1

- Hint: Spectral series is obtained when an atom emits energy while making transition from higher energy level to lower energy level. Different lines in the spectral series corresponds to different amounts of energy released. A hydrogen atom consists of an electron revolving around the nucleus.

Complete step-by-step solution -
A hydrogen atom consists of an electron orbiting around the nucleus. The electron can orbit in different orbits called energy levels. When it makes transition from higher energy level to lower energy level, it emits energy in the form of light. The wavelength of emitted light depends on transition levels. This gives rise to the emission spectrum of hydrogen which consists of different spectral lines corresponding to each transition.
The wavelength of emitted light is given by Rydberg formula,
\[\dfrac{1}{\lambda }=R{{Z}^{2}}(\dfrac{1}{{{p}^{2}}}-\dfrac{1}{{{n}^{2}}})\]
Where, R is Rydberg constant = $1.09737\times {{10}^{7}}{{m}^{-1}}$
     Z is atomic number (for hydrogen Z=1)
     P is lower energy level
     n is higher energy

Spectral lines appearing in hydrogen spectrum:
1. Lyman series:
A series of spectral lines obtained when an electron makes a transition from any high energy level (n=2, 3, 4, 5….) to first energy level (p=1) is termed as Lyman series. It lies in the ultraviolet region of the electromagnetic spectrum.
2. Balmer series:
A series of spectral lines obtained when an electron makes a transition from any high energy level (n=3, 4, 5, 6….) to second energy level (p=2) is termed as the Balmer series. It lies in the visible region of the electromagnetic spectrum. The first line in the series (n=3 to p=2) is called ${{H}_{\alpha }}$ line, the second line in the series (n=4 to p=2) is called \[{{H}_{\beta }}\] line, etc.
3. Paschen series:
A series of spectral lines obtained when an electron makes a transition from any high energy level (n=4, 5, 6, 7….) to first energy level (p=3) is termed as the Paschen series. It lies in the infrared region of the electromagnetic spectrum.
4. Brackett series:
A series of spectral lines obtained when an electron makes a transition from any high energy level (n=5, 6, 7, 8….) to first energy level (p=4) is termed as Brackett series. It lies in the infrared region of the electromagnetic spectrum.
5. Pfund series:
A series of spectral lines obtained when an electron makes a transition from any high energy level (n=6, 7, 8, 9….) to first energy level (p=5) is termed as Pfund series. It lies in the infrared region of the electromagnetic spectrum.

Note: A spectrum is the footprint of an atom. It is unique for a given atom. From the spectrum we can deduce many properties and characteristics of an unknown sample such as its electronic configuration, its shape, crystal structure etc. There are different types of spectroscopic techniques available to get a spectrum of a given sample.