Bohr's Atomic Model, Its Merits and Limitation - Chemistry Class 11

Chemistry Notes | Science
Bohr's Atomic Model and Its Advantages and Limitation
Class: 11

In 1913 German Scientist Neils Bohr proposed the model of an atom which was based upon the plank’s quantum theory of radiation. The basic postulates of Bohr’s theory are:

1. An atom consists of a small, heavy, positively charged nucleus in the centre and electron revolves around it in a circular orbit. 

2. The energy of the electron in a particular energy level remains constant i.e. electron neither loss nor gain energy during revolution in a certain energy level.

3. Only those selected orbits are permissible in which the angular momentum of an electron is equal to the integral multiple of (h/2π), i.e. angular momentum (mvr) = (nh/2π). 

Where, 

m = mass of electron.

V = velocity of electron

R = radius of orbit

N = number of orbit,

H = plank’s constant = (6.62 X 10)-34 JS

4. The energy is emitted or absorbed only when the electron jumps from one energy level to another energy level. When energy is supplied, electron absorbs energy and jumps from lower level to higher level and it loss energy when it jumps from higher energy level to lower level. The amount of energy absorbed or emitted can be calculated by the following relation: 

∆E = E2 – E1 = hv

Where, 

∆E = Energy lost or absorbed

E2 = Energy of electron in higher energy level.

E1 = Energy of electron in lower energy level.

Merits (Usefulness) of Bohr’s Atomic Model:

1. It can answer the question of losing of energy continuously of an electron and falling into the nucleus because an electron doesn’t loss energy when it is revolving in a particular orbit. 

2. It helps to calculate the radius of the orbit by following relationship: 

R = (E(n^2)(h^2))/(Z(e^2)πm)

Where,

n = energy level

h = plank’s constant

E = vacuum permittivity = 8.85 × 10^(-12) A^2/kgm

Z = Atomic number or proton number.

E = Energy of electron 1.6 × 10^(-19)

M = mass of electron

3. It also helps to calculate energy of the electron present in definite energy level by following relationship: 

E = {(Z^2) (e^4)m}/{8(e1^2)(n^2)(h^2)}

Limitation of Bohr’s Theory of Atom:

Following are the limitation of Bohr’s theory of atom:

1. It couldn’t explain the origin of spectral lines in multielectral system. 
2. It couldn’t explain the splitting of spectral line into final lines in a presence of magnetic field (Zeeman effect) and in the presence of electric field (Strak field) 
3. It couldn’t explain the three dimensional structure of atom but it indicates thatstructure of atom. 
4. It couldn’t explain the combination of molecules and their structure.

Read This Also:

• Rutherford's α-rays Scattering Experiment | Chemistry Class 11
• Boyle's Law - Graphical Representation and Application | Chemistry Class 11
• Old Question Paper 2070 - Chemistry Class 11 | Download
• The Magic of Words - Complete Summary | Compulsory English Class 11

Don't forget to LIKE, SHARE and COMMENT. Please join with us on Facebook and Google+ for daily Notes and Subscribe for our Email Updates.