Spectrum is a sequence of radiations of specific wavelengths being emitted from a specific source. When atoms absorb or emit radiations, similar patterns are formed. An atom can form various types of spectrums.
In this article, you will be studying various types of absorption and emission spectrums that an atom might form.
Types of Spectra
Atomic Emission Spectrum
When the radiation emitted from a light source is passed through the prism and then received on the screen then the colorful spectrum that is obtained is called as emission spectrum. There are three types of emission spectra that various substance can form.
1. Continuous Emission Spectrum
When a narrow beam of white light is passed through a prism, it is dispersed into 7 colors from violet to Red.
2. Line Emission Spectrum
When an atomic gas is subjected to electrical excitation, it first absorbs energy & then gives it out as radiation. On examining these radiation through a spectroscope a spectrum is obtained which has well defined lines, each corresponding to a specific wave length. These lines are separated from each other by dark space. This type of Emission spectrum is called as Line emission spectrum.
1. No two elements will have identical line spectrum because energy levels are different in every element. Therefore, the line spectra of the elements are described as finger prints differing from each other like the finger prints of the human beings.
2. Since line spectrum is obtained by the emission of energy through the atoms of the element therefore line spectrum is also called as atomic spectrum.
3. Hydrogen atom also gives a line spectrum which was explained well by the Bohr's Model. Bohr' model for hydrogen atom will be covered later in this chapter.
3. Band Emission Spectrum
If molecular form of the gas is used, it first absorbs energy for not only electron transition but for rotational, vibrational and translational then emits radiations. On examining these radiations through a spectroscope a spectrum is obtained on the screen, which shows groups of closely packed lines called Bands. Therefore, this type of spectrum is called a Band emission spectrum. Bands are separated from each other by dark space.
Absorption Spectrum
When white light is first passed through a solution or vapors of chemical substance or gas and then analyzed by spectroscope, it is observed that some dark lines are obtained in otherwise continuous spectrum. This type of spectrum is called as Absorption spectrum.
- If white light is passed through atomic gas then the obtained spectrum is called as Absorption line spectrum.
- If white light is passed through molecular gas then the obtained spectrum is called as Absorption band spectrum.
Line Spectrum of Hydrogen Atom
When an electric excitation is applied on atomic hydrogen gas at Low pressure, a bluish light is emitted. when a ray of this light is passed through a prism, a spectrum of several isolated sharp line is obtained. The wavelength of various lines show that spectrum lines lie in Visible, Ultraviolet and Infra red region.
These lines are grouped into different series.
The line spectrum of hydrogen atom was explained by Bohr atomic model which will be studied later in this chapter.
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