Question

What is emission spectrum and absorption spectrum? And what are the difference between them?

Answer 1

) The emission spectrum of a gas is represented by a collection of separate colored lines, with dark spaces between them. The lines are the parts of the spectrum where emission occurs and photons are emitted, while the dark spaces are the parts where there is no emission, hence the darkness. The difference in colors is due to the variation of the energy levels of the electrons.
b) In case of ionic solutions, the spectrum will consist of discrete colored bands instead of lines, since the substance here is a compound with different atoms, which together produce complex colors. Emission spectrum is different for different elements subjected to the same source of energy, due to the difference in the excitation energies of the different electrons of the substances. This is why the light emitted by each substance is different.
c) The frequency of emission spectrum are frequencies of light that are dependent on the energy of the emission. The energy of the photons emitted is related to its frequency by the following formula:
E=hν
Where E = energy of the photon
h = Planck's constant
ʋ = frequency of the photon
This shows that the frequency of a photon is directly proportional to its energy.
d) Emission spectra can be divided into two: line spectrum and continuous spectrum. When the spectrum appears as a series of lines, which are separated by black spaces, it is called a line spectrum. When the spectrum consists of a wide range of colors in a particular wavelength range or interval, it is called continuous spectrum.
e) The absorption spectrum of an element is represented by a continuous band of colors with separate dark lines between them. The entire band represents the total light that is focused on the element. The dark lines are the parts of the spectrum where the electrons absorb light photons, hence, there is absence of light at these parts. The remaining colored parts of the spectrum represent the parts of the incident light that has not been absorbed, and hence, appear as wavelength-specific colors.
f) The reason for this pattern is that, all electrons of an atom are at different energy levels at any given time. The energy difference between two energy levels of each electron is different. When light of any wavelength is focused on these atoms, each electron will absorb only that photon with the same energy as this energy difference. The rest of the photons are not absorbed, i.e., these photons are scattered. These dark lines correspond to the same positions where the colored lines of the atom's emission spectrum would occur.
g) Absorption spectra can be measured in terms of their frequency, wavelength, or wave number.
h) There are two types of absorption spectra: atomic absorption spectrum and molecular absorption spectrum. Atomic absorption spectrum is the spectrum obtained when free atoms (generally gases) absorb wavelengths of light. Molecular absorption spectrum on the other hand is the spectrum that is seen when molecules of a substance absorb wavelengths of light (generally ultraviolet or visible light).