Key Concepts: Atomic Models

Historical Atomic Models

• Thomson's "Plum Pudding": Positive charge spread uniformly with electrons embedded in it.
• Rutherford's Nuclear Model: Most of the atom is empty space; mass and positive charge concentrated in a tiny nucleus. Discovered via gold foil experiment.
• Bohr Model: Electrons orbit the nucleus in fixed energy levels (n = 1, 2, 3...). Electrons can only gain or lose energy by jumping between levels.
• Quantum Mechanical Model: Electrons exist in probability clouds (orbitals), not definite paths.

Bohr Model Details

• Energy levels: E_n = −13.6/n² eV (for hydrogen).
• Photon emission: ΔE = hf = E_upper − E_lower.
• Spectral lines correspond to transitions between specific energy levels.

Line Spectra

• Emission spectrum: Bright lines from hot gas — electrons dropping to lower levels.
• Absorption spectrum: Dark lines where light is absorbed — electrons jumping to higher levels.