Atomic spectra class 11th and 12th


Have you watched those scientific movies, where the whole planet gets destroyed due to some sort of radiation or atomic waves. Well in this article we are going to take a look at one aspect of radiation known as "atomic spectra".

At first, this word may scare you, but don't worry we will break it into simpler terms for you in this article and cover all things regarding atomic spectra.

If I have to explain atomic spectra in short terms:

When electron gets in excited state from one energy level to the other, electron either emits or absorbs lights of a specific wavelength. The total collection of all these specific wavelengths of the atom in a given set of the condition is known as atomic spectra.

This spectrum of electromagnetic radiation is emitted or absorbed by an electron during the transition from one energy level to another is what you refer to as atomic spectra. 

What are atomic spectra ?

As I said earlier, when electrons get into an excited state, theses electrons absorb or emit electromagnetic radiation which forms a spectral line of wavelength associated with that atomThe total collection of all these wavelengths or spectral lines is known as atomic spectra. 

We all have seen atomic spectra at least ones in our life, 7 coloured rainbow is one of the common examples of atomic spectra of white light which you can also see after passing through a prism.

Even, atomic spectra are of three different types: 1. Emission Spectra 2. Absorption Spectra 3. Continuous Spectra. 

  Continuous spectrum v/s Emission Spectrum v/s Absorption spectrum 
Continuous spectrum v/s Emission Spectrum v/s Absorption spectrum 
Rainbow and spectrum form by splitting of white light through a prism is a continuous spectrum. We will have a look at the emission and absorption spectrum later in this article, but before that, let's first learn about what is spectral series which is a part of atomic spectra as well,  especially the spectral series of a hydrogen atom.

Spectral series:

When an electron gets into an excited state, an excited state is unstable for an atom, the electron tries to return back to the ground state by emitting the energy of a particular wavelength. So spectral series is the set of wavelength arranges in a sequential manner, which gives the characteristic of light and electromagnetic radiation by an energized atom.

Spectral series of a hydrogen atom:

Hydrogen has the simplest atomic system which can be found in nature and therefore the spectral series of a hydrogen atom is also the simplest of all which makes it essential to learn to get the concept clear of atomic spectra.

Here is the image of spectral series of the hydrogen atom:

Spectral series of the hydrogen atom

From the above image, you can see that a spectral series of a hydrogen atom is divided into several spectral lines with a wavelength that can be found with the help of Rydberg formula (We will talk about it later in this article!)

These spectral lines are due to the atomic transition of a hydrogen atom between different energy levels.

So, let's have a look at the Rydberg formula to find the wavelength of spectral lines in the hydrogen atomic spectrum.

Rydberg formula:

Rydberg formula is used to calculate the wavelength of spectral series:

Here,
  • λ = wavelength
  • R = Rydberg constant
  • Z = atomic number
  • n= lower energy level
  • n=  higher energy level         

Refer to this table for better understanding of spectral series of the hydrogen atom:

Series n λ
Lyman Series (n=1): 2 121.57
3 102.57
4 97.256
5 94.974
6 93.78
91.175
Balmer Series (n=2): 3 653.3
4 486.1
5 434.0
6 410.2
7 397.0
364.6
Paschen Series (n=3): 4 1875
5 1282
6 1094
7 1005
8 954.6
820.4
Brackett Series (n=4): 5 4051
6 2625
7 2166
8 1944
9 1817
1458
Pfund Series (n=5): 6 7460
7 4654
8 3741
9 3297
10 3039
2279
Humphreys Series (n=6): 7 12.37
8 7.503
9 5.908
10 5.129
11 4.673
3.282

Atomic spectroscopy:

The study of electromagnetic radiation absorbed or emitted by an atom is what we called as Atomic Spectroscopy. Even there are three kinds of Atomic spectroscopy: 1. Atomic emission spectroscopy 2. Atomic adsorption spectroscopy and 3. Atomic fluorescence spectroscopy. 

Now, let's have a look at what emission and absorption spectrum is, and with this, we have covered all the basic concepts of types of atomic spectra for class 11th and 12th.  

Use of atomic spectroscopy:

There are large varieties of the field where atomic spectroscopy is used and we will be mentioned only few of them:
  • Clinical analysis of metal in biological fluids and tissues.
  • In the pharma industry to find the traces of materials used.

Emission spectrum:

When electromagnetic radiation gets interacted with a matter, molecules or atom, its electrons get into the excited state. This excited state of an atom is unstable and therefore it wants to get normal like before and get again into the ground state.

In order to achieve ground state back, atoms emit some amount of energy which it had absorbed earlier.

Light of specific wavelength is formed depending upon the amount of energy emitted by an atom to return to its ground state. This spectrum of radiation emitted by an atom is called an emission spectrum.

Absorption spectrum:

An absorption spectrum is constituted by the frequencies of light transmitted with dark bands when energy is absorbed by the electrons in the ground state to reach the higher energy state.

The absorption spectrum comprises of dark lines or gaps in the spectrum.

Difference between Absorption spectrum and Emission spectrum
Here is the table to differentiate between emission spectrum and absorption spectrum:

Absorption spectrum Emission spectrum
Is created when electron absorbs energy to reach higher energy state from a ground state. Is created when electron emits energy to reach ground state from the higher energy state.
Comprises of dark lines and gaps in the spectrum. Comprises of colour lines in the spectrum.
Used to find the ability of a certain object to retain and its absorption level. Used to find the composition of a certain matter.
The wavelength of light absorbed is helpful in figuring out the quantity of a substance in the sample. Type of photon emitted during emission is used to find out the element the substance is made of as each element radiate a different amount of energy and has different emission level.

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