Bohr's Atomic Theory (1913)

Neil Bohr presented this theory to fix the problems in Rutherford's model. He used the quantum theory (proposed by Max Planck) and studied the hydrogen atom as a model.

Main Assumptions / Postulates:

1. Electrons revolve in fixed circular paths called shells, orbits, or energy levels.
2. Each orbit has a fixed energy. The farther the orbit from the nucleus, the higher the energy.
3. As long as an electron stays in its orbit, it does not gain or lose energy.
4. When an electron jumps from a higher orbit to a lower orbit, it releases energy.
5. When an electron jumps from a lower orbit to a higher orbit, it absorbs energy.
6. Energy difference formula: ΔE = E₂ − E₁ = hv (where h = Planck's constant, v = frequency)
7. Angular momentum of electron: mvr = nh/2π

Shells and Their Maximum Electrons (Formula = 2n²):

Shell 1 (K) — Maximum 2 electrons 

Shell 2 (L) — Maximum 8 electrons 

Shell 3 (M) — Maximum 18 electrons 

Shell 4 (N) — Maximum 32 electrons 

Shell 5 (O) — Maximum 50 electrons

Important: Formula for maximum electrons in any shell = 2n² where n is the shell number.