Bohr’s Theory of Hydrogen Spectra

Hydrogen spectra is interpreted on the basis of Bohr’s atomic model as follows:

When electric discharge is passed through hydrogen gas, first of all hydrogen molecules split into atoms. Then, hydrogen atom absorbs more energy where by electrons are promoted to higher energy level. The electrons in higher energy level are unstable, hence jumps to lower energy level which give rise to spectra.

The wavelength of the light emitted depends upon the energy difference between higher energy level and lower energy level.

where,

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

R = Rydberg’s constant

λ = wavelength of radiation emitted

n1 = lower energy level

n2 = higher energy level

The spectral lines are diagrammatically represented as:

Energy level diagram of hydrogen atom

1. Lymen series: The series of spectral lines which is formed due to the falling of electron from different higher energy level to the first energy level is called lymen series. This series lies under ultraviolet region.

2. Balmer series: The series of spectral lines which is formed due to the falling of electron from different higher energy level to the second energy level is called balmer series. This series lies under visible region.

3. Paschen series: The series of spectral lines which is formed due to the falling of electron from different higher energy level to the third energy level is called paschen series. This series lies under infra red region.

4. Brackett series: The series of spectral lines which is formed due to the falling of electron from different higher energy level to the fourth energy level is called brackett series. This series lies under middle infra red region.

5. P-fund region: The series of spectral lines which is formed due to the falling of electron from different higher energy level to the fifth energy level is called p-fund series. This series lies under far infra red region.

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