Bohr’s Model of the Atom (1913)
Niels Bohr proposed an improved atomic model to address the limitations of Rutherford’s model. He introduced quantized energy levels to explain atomic stability and spectral lines.
Postulates of Bohr’s Atomic Model
Electrons move in fixed circular orbits around the nucleus without radiating energy.
Only certain allowed orbits (energy levels) exist, where electrons do not lose energy.
Energy is absorbed or emitted only when electrons jump between energy levels:
Absorption: Electron moves to a higher energy level (excited state).
Emission: Electron moves to a lower energy level, emitting energy as light (spectral lines).
Angular momentum of an electron is quantized and follows the equation:
mvr=nh2πmvr = \frac{nh}{2\pi}
where n = principal quantum number (1, 2, 3…), h = Planck’s constant, m, v, r = mass, velocity, and radius of the electron’s orbit.
Energy Levels (Shells: K, L, M, N)
Bohr described discrete energy levels (shells), denoted by letters:
| Shell | Principal Quantum Number (n) | Maximum Electrons |
|---|---|---|
| K | 1 | 2 |
| L | 2 | 8 |
| M | 3 | 18 |
| N | 4 | 32 |
Electrons occupy the lowest energy level (K) first before moving to higher levels.
Each shell corresponds to a specific energy, increasing as n increases.
Diagram: Bohr’s Model of Hydrogen Atom
(A labeled diagram showing a nucleus at the center with electrons revolving in quantized energy levels: K, L, M, and N shells.)