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What is the Hydrogen Spectrum?

In chemistry, we read about the excitation of atoms or molecules, from lower energy level to higher energy level, on absorbing energies. When the same amount of energy is emitted by the excited atom, it moves back to its ground state. We observed the same phenomenon while studying the hydrogen emission spectrum.

Whenever a gaseous hydrogen molecule is passed across an electric discharge tube, the hydrogen atoms, comprising the molecules, disintegrate by absorbing the energy and transit to higher energy levels. To move back to the ground state, these atoms emit the same amount of energy in the form of a series of radiations, which is called the hydrogen spectrum.

Related: Read these articles to learn the technique of spechrophotometery and capillary zone electrophoresis.

Why is the Hydrogen Emission Spectrum Important?

The emission spectrum of hydrogen comprises a vast spectral series. This spectral series, in turn, consists of radiations of different wavelengths which help in astronomical analysis - to detect the presence of hydrogen in space.

During the formation of the line spectrum of hydrogen, a hydrogen molecule is broken down into atoms. These atoms absorb energy, jump to higher energy levels, emit energy and jump back to lower energy levels. Thus, this atomic emission spectrum helps us to understand the concept of energy levels.

Related: Also learn the different gas law and its properties along with the laws of thermodynamics with examples.

How is Hydrogen's Emission Spectrum Produced?

When a gas tube is filled with hydrogen gas at low pressures, wherein two electrodes are placed at the opposite ends (also called the hydrogen tube), and a voltage of about five thousand volts is applied across it, a bright pink light is emitted by the tube.

On passing this bright pink glow light from a diffraction grating or prism, this light is further split into various lights, having different wavelengths. This hydrogen emission lines of radiation we gain is called the hydrogen emissions spectrum. Most of the part of this hydrogen emission spectrum consists of invisible radiations, including infrared and ultraviolet radiations.

How is the Atomic Emission Spectrum of Hydrogen Produced?

When the electric charge of a specific voltage is applied across the glass tube, filled with hydrogen gas, it emits light (of various wavelengths and colors). When the light is passed through a diffraction grating, we get almost four bands of visible lights against the pitch-black background.

These four narrow bands of visible light contain red light, violet light, violet-blue light, and blue-green light. Besides this series of visible light, some more radiation is also emitted by the hydrogen atoms. Those radiations cannot be seen by the naked eye since they belong to the infrared and ultraviolet wavelengths range.

Thus, by using the same principle of producing hydrogen's emission spectrum, we produce the atomic emission spectrum of the hydrogen atom with a band of visible and invisible lights.

Related: Read how to find percent yield & determining conversion factors on this site.

How do you Find the Wavelength of the Hydrogen Spectrum?

To study the whole band of radiations, we divide the spectrum into multiple series based on their specific wavelength range like the Lymen series, Paschen series, Balmer series, etc.

Related: Also find Zeeman effect in NMR spectroscopy

The Lyman series of the hydrogen emission lines is the easiest one to study and comprises radiations having wavelengths of (2.5-3.5) - the ultraviolet range. The Paschen series consists of Infrared radiations having wavelengths of 0-0.5 whereas the Balmer series comprises partly visible radiations having wavelengths of 0.5-1.0.

The question which arises here is how you can find out the wavelength of every radiation present in the line spectrum of hydrogen. For this purpose, we use a mathematical equation that shows a connection between wavelength and frequency such as

c = λv

Here, c is the speed of light, λ is frequency while v is the wavelength. On rearranging the equation a bit, we get the formula using which we could derive the wavelength of given radiations as follows

λ = c/v
v = c/λ

From the given relation, it's clear that both the values of frequency and wavelength are inversely proportional to each other. The higher the frequency, the lower will be the wavelength and vice versa.

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