Bohr's Atomic Model | Definition | Postulates | Explanation | thetutee

 

Introduction

Neil Bohr was a Danish physicist who put forward a theory in 1913 regarding the atomic structure of the atom known as the Bohr’s atomic model. His ideas were quite different from the classical model in fact, he was one of the first scientist to use the quantum model. In his experiment he used the Hydrogen atom (Z= 1) to describe the atomic structure of the atom.

Once Einstein extended planks idea of energy quantization to the electromagnetic radiation other physicist made the similar strides. Neil Bohr was constantly searching for the exact structure of the atom. In his mind he constantly faces following questions.

If an atom has positively charged protons and negatively charged electrons, why are they stable? Why don’t they collide with each other despite being positively charged? What are these emission spectra lines that we see of different types of elements and why they emit different colors?

Bohr then tried to answer this question with his model extending the idea of energy quantization and said that potential energy of electron in the Hydrogen atom is also quantized. The postulates of his model are as follows.

• The electrons revolve around the nucleus in a fix energy level which are called as shells.
• He said that each electron in different energy levels have different energies. An electron can move from one energy level to another energy level when it absorbs or emit photon. ΔE_electron = E_photon    

              OR  ΔE = hf = E_i − E_f

• The energy levels are represented by integers like (n = 1, 2, 3….). The shells are also be named as (K, L, M…), the lowest energy level is also called as ground state.
• He also put forward the mathematical formula for Angular momentum,

 

ℓ = angular momentum

n = principal quantum number

h = Planck’s constant

π = 3.14

LIMITATIONS OF THE BOHR’S ATOMIC MODEL

• Because it considers electrons to have both a known radius and orbit, it infringes the Heisenberg Uncertainty Principle.

• The Bohr Model gives an inaccurate value for the orbital angular momentum of the lowest energy state.

• It has a terrible track record when it comes to predicting the spectra of heavier elements.

 

• The relative intensities of spectral lines are not predicted.

 

• Fine and hyperfine structure in spectral lines is not explained

 

• It doesn't account for the Zeeman Effect.