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# Line spectra of hydrogen atom

Line spectra of hydrogen atom

Line spectra of hydrogen atom is an important topic for JEE because problems from this topic are asked in JEE Physics as well as JEE Chemistry.

Bohr's model: The Bohr's Model is central to the understanding of line spectra of Hydrogen atom. The postulates by Bohr help to derive important results about Hydrogen spectra.
1.    Angular momentum of an electron is an integral multiple of h/2π
2.    The electrostatic force of attraction between the electron and the nucleus provides the necessary centripetal acceleration which is needed for the electron to stay in the orbit

For a single electron system such as a hydrogen atom, the analysis is fairly easy. However, it becomes complex for multi electron systems.

The spectrum of Hydrogen atom was studied by various scientists and Bohr's model of hydrogen atom helps us to understand the spectra. When an electron jumps from a higher energy state to a lower energy state, it emits energy.

This energy is given out as a photon of light. This photon explains the observed spectra. Accordingly, we have 5 series of spectra:
1.    Lyman series – ultra violet light is emitted when an electron jumps from a higher energy state to the n = 1 state. The corresponding series is called as Lyman series
2.    Balmer series - visible light is emitted when an electron jumps from a higher energy state to the n = 2 state. The corresponding series is called as Balmer series
3.    Paschen series – infrared light is emitted when an electron jumps from a higher energy state to the n = 3 state. The corresponding series is called as Paschen series
4.    Brackett series – far infrared light is emitted when an electron jumps from a higher energy state to the n = 4 state. The corresponding series is called as Brackett series
5.    P-fund series - far infrared light is emitted when an electron jumps from a higher energy state to the n = 5 state. The corresponding series is called as P-fund series

The entire hydrogen spectra can be explained using just 1 equation – the Rydberg's equation:

Students are advised to memorize the most common energy level (n = 1, 2, 3) in electron volts as well as in joules. This will help them in faster calculation in examination pressure. For example, it is good to remember that the energy of first Bohr's orbit is -13.6 eV and that of second Bohr's orbit is -3.4 eV.

Students should also be aware of the concept of Ionization potential. It is the least amount of energy needed to completely remove the electron from the system. Ionization potential is nothing, but the energy that we must give to the system to make the total energy = 0. For example, the ionization potential of first Bohr's orbit = 13.6 eV

Students should also remember the value of Rydberg's constant. This will help them in faster calculation during examination.