 # Bohr Model:

(Bohr’s atomic model for hydrogen atom)

Neils Bohr’s, 1913 proposed a model of an atom based on the planks quantum theory of radiation.

## Main Postulates of Bohr’s theory:

The basic postulates of Bohr’s theory are:

1. An atom consists of small, heavily positively charged nucleus around which electrons revolve in definite circular paths called orbits.
2. These orbits are associated with definite energies called energy shells or energy levels. They are designated as K, L, M, N, O…..etc. shells or numbered as 1,2,3,4,5,…. etc. from the nucleus.
3. As long as the electrons remain in a particular orbit/energy shell their energy remains constant. This accounts for the stability of an atom.
4. Only those orbits are permitted in which the electron’s angular momentum is a whole number multiple of h/2π where h is Planck’s constant. Any moving body taking a circular orbit has an angular momentum equal to the product of its mass (m), velocity (v) and radius of orbit (r).

In other words the angular momentum of an electron

mvr = n h/2π

Where n= 1, 2, 3…

5. Electrons can either lose or absorb energy abruptly when they jump from one energy level to another. For instance, when an electron moves from normal or ground state E1 of an atom i.e. the state of lowest energy as required by its ‘n’ and ‘l’ values, to a higher level, it causes the atom to be in its excited state E2 i.e. where electrons of an atom occupy energy levels higher than those permitted by its ‘n’ and ‘l’ values. The reverse is also true and the change in energy is:

## Recommended video!

Bohr’s Atomic Model

Defects of Bohr’s atomic model

Rutherford’s Atomic model

Planck’s Quantum Theory

Gas Discharge Tube Experiment

## What does Bohr model explain?

According to the Bohr model, electrons orbit the nucleus at constant energy levels. Energy levels are greater in orbits further from the nucleus. When electrons return to a lower level of energy, they emit light as a kind of energy.

## What are the major features of Bohr model?

1) The orbits of electrons around the nucleus are circular and contain constant energy.
2) The electron only orbits in circular orbits whose angular momentum is a multiple of nhi/2.
Only when an electron transitions from one orbit to another is energy realised or absorbed in the form of a photon.

## Did Bohr’s model have neutrons?

In the Bohr model of the atom, the nucleus holds the majority of the atom’s mass in its protons and neutrons. The positively charged core is surrounded by negatively charged electrons, which contribute minimal mass but are electrically equivalent to the protons in the nucleus.

## How did Bohr discover electrons?

Bohr was the first to discover that electrons move in distinct orbits around the nucleus and that the quantity of electrons in the outer orbit determines an element’s properties.

## What is the limitation of Bohr Atomic Model Theory?

The Bohr Atomic Model Theory is incapable of explaining the influence of magnetic field on atomic spectra. In addition, neither the Stark effect nor the Heisenberg Uncertainty Principle was explained.

## What is the importance of Bohr’s theory of the atomic model?

Bohr was the first to discover that electrons move in distinct orbits around the nucleus and that the number of electrons in an element’s valence shell determines its properties.

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