Hydrogen Spectrum - Practice Questions & MCQ

When an electric discharge is passed through gaseous hydrogen, the H₂ molecules dissociate and the energetically excited hydrogen atoms produced emit electromagnetic radiation of discrete frequencies. These radiations are emitted because of electronic transitions upon de-excitation to different energy levels and on the basis of the final energy level of transition, the hydrogen spectrum consists of several series of lines named after their discoverers like Lyman series, Balmer Series, Paschen Series, Bracket Series, Pfund Series.

Line Spectrum of Hydrogen-like atoms

$\frac{1}{\lambda}=R Z^2\left(\frac{1}{n_1^2}-\frac{1}{n_2^2}\right)$

Where R is called Rydberg constant, R = 109677cm^-1,  Z is atomic number

n₁= final orbit occupied after de-excitation= 1, 2, 3….

n₂= initial orbit occupied before de-excitation

Lyman Series spectrum:

Transition of electrons from higher orbits to n=1 result in the Lyman Series

n₁= 1 and  n₂= 2, 3, 4....

For H atom, this lies in Ultraviolet region. For elements with higher Z, the Balmer lines lie in the Ultraviolet region

Balmer Series Spectrum:

Transition of electrons from higher orbits to n=2 result in the Balmer Series

Where n₁= 2 and  n₂= 3, 4, 5, 6....

For H atom, this generally lies in visible region.

Paschen, Bracket and Pfund Series spectrums:

Transition of electrons from higher orbits to n=3, 4 and 5 respectively result in the Paschen, Bracket and the Pfund Series

These lines lie in the Infrared Region for H atom.

Discovery of the line spectrum gave the evidence for quantised electronic energy levels in atoms and laid the foundation for the development of the Bohr's model.