What are the postulates of Bohr’s model of hydrogen atom? Discuss the importance of this model to explain various series of line spectra in hydrogen atom.

Postulates of Bohr’s Model:
1) The electron in an atom revolve round the nucleus in certain fixed circular paths called orbits (or) shells.
2) Each orbit is associated with fixed energy is called energy level. They are 1, 2, 3, …. and are also designated by K, L, M, …..
3) As long as an electron revolves in a permitted orbit it neither loose nor gain energy hence these orbits are called stationary orbits.
4) When an elctron jumps from a lower orbit to a higher orbit, it absorbs energy when an electron jumps from higher orbit to lower orbit, it emits energy. The emitted or absorbed energy is given by $\mathrm{\Delta E}={\mathrm{E}}_2-{\mathrm{E}}_1=\mathrm{h\vartheta }$
E₂ = Energy of higher orbit
E₁ = Energy of lower orbit
5) The angular momentum of an electron moving around the nucleus is quantized.
$\therefore \mathrm{mvr}=\frac{\mathrm{nh}}{2\mathrm{\pi }}$
Where m = mass of an electron
v = velocity of an electron
r = radius of an orbit
n = principle quantum number
h = planck’s constant
$=6.625\times {10}^{-27}\text{ erg.sec }$
Hydrogen Spectrum : When hydrogen gas is subjected to silent electric discharge. The electron of hydrogen atom gets excited to various excited levels and deexcited to form various spectral lines in various regions is called hydrogen spectrum. Hydrogen spectrum contains 5 series of lines.
Lyman Series: Lyman series is formed when an electron jumps from any one of the higher orbit to first orbit. It is observed in uv region. Balmer Series: Balmer series is formed when an electron jumps from any one of the higher orbit to second or bit. It is observed in visible region.
Paschen Series: Paschen series is formed when an electron jumps from any one of the higher orbit to third orbit. It is observed in middle IR region.
Brackette Series: Brackette series is formed when an electron jumps from any one of the higher orbit to fourth orbit. It is observed in middle IR region.
Pfund Series: Pfund series is formed when an electron jumps from any one of the higher orbit to fifth orbit. It is observed in far IR region.