Question

Differentiate between absorption and emission spectrum.

Answer 1

Hint: When a radiation is passed through a prism for the dispersion of radiation, the pattern so obtained on the screen (photographic plate) is called a spectrum of that radiation.

Complete answer:
There are two types of spectrum a) absorption spectrum b) emission spectrum. First, we will discuss the absorption emission. When a beam of electromagnetic radiation is passed through a chemical sample, a part of it is absorbed. Electromagnetic energy is transferred to the atoms or molecules in the sample and therefore the particles get promoted to higher energy level (excited state) from lower energy level. At room temperature, they are at ground state. Thus absorption spectrum involves transition from ground state to excited state. In other words we can say that an absorption spectrum is a plot of the amount of light absorbed Vs the wavelength of light. The amount of light absorbed is called absorbance. An absorbance spectrum is obtained by using a spectrophotometer to scan a particular wavelength region and to observe the amount of light absorbed by the sample along the way. For example, consider the \[CuS{O_4} \] solution, it displays a blue colour which means that the blue portion of the visible region is absorbed but is transmitted to our eyes. Now talking about the emission spectrum, when excited atoms, ions or molecules return back to their ground state electromagnetic radiations are produced. Excitation is possible by various means such as flames, arcs. Radiating particles produce radiations of definite wavelength producing continuous or line spectra. A continuous line spectrum consists of wavelengths which are closely spaced.

Note:There are three basic processes by which a molecule can absorb radiation, and these are as follows:
a) Rotational transition
b) vibrational transition
c) electronic transition