Structure of Atom (Part 6)

Bohr's Atomic Theory:

Keeping in view the defects in Rutherford's Atomic Model, Neil Bohr presented another model of atom in 1913.The Quantum Theory of Max Planck was used as foundation for this model. According to Bohr's model, revolving electron in an atom does not absorb or emit energy continuously. The

energy of a revolving electron is 'quantized' as it revolves only in orbits of fixed energy, called 'energy levels' by him.

The Bohr's atomic model was based upon the following postulates:

i. The hydrogen atom consists of a tiny nucleus and electrons are revolving in one of circular orbits of radius ‘r’ around the nucleus.

ii. Each orbit has a fixed energy that is quantized.

iii. As long as electron remains in a particular orbit, it does not radiate or absorb energy. The energy is emitted or absorbed only when an electron jumps from one orbit to another.

iv. When an electron jumps from lower orbit to higher orbit, it absorbs energy and when it jumps from higher orbit to lower orbit it radiates energy. This change in energy, E is given by following Planck's equation.

Where, h is Planck's constant equal to 6.63×10−34 Js, and v is frequency of light.

v. Electron can revolve only in orbits of a fixed angular moment mvr, given as:

Where 'n' is the quantum number or orbit number having values 1,2,3 and so on.

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