Comprehensive notes, Subatomic Particles, Rutherford and Bohr's Atomic Models, Quantum Numbers, and Electronic Configuration for Chapter 2, 11th Class Chemistry.
Electron (e-): Discovered by J.J. Thomson in Cathode Ray Tube experiments. Negatively charged, mass 9.1 × 10-31 kg.
Proton (p+): Discovered by Goldstein (as Canal Rays) and Rutherford. Positively charged, mass 1.67 × 10-27 kg (1836 times heavier than electron).
Neutron (n): Discovered by Chadwick (1932). Neutral particle, mass slightly greater than proton.
Rutherford's Model: Nucleus at center, electrons orbit like planets. Defects: Predicts continuous spectrum and eventual collapse of spiraling electron.
Bohr's Model: Electrons orbit in fixed energy levels (shells). Energy change (ΔE) occurs only when jumping orbits. ΔE = E2 - E1 = hν. Defects: Failed to explain spectra of multi-electron atoms, Zeeman effect (magnetic splitting), and Stark effect (electric splitting).
Set of 4 numbers describing an electron's state:
Aufbau Principle: Electrons fill lowest energy orbitals first (1s < 2s < 2p...).
Pauli's Exclusion Principle: No two electrons can have the same set of 4 quantum numbers (must have opposite spins).
Hund's Rule: Degenerate orbitals (e.g., px, py, pz) are filled singly with parallel spin before pairing.
Chromium (24Cr): [Ar] 3d5 4s1 (Half-filled stability).
Copper (29Cu): [Ar] 3d10 4s1 (Fully-filled stability).