Discovery of Subatomic Particles and Atomic Models

Introduction

This session is intended for students who have already studied the chapter and want a quick revision.
The structure of the atom plays a crucial role and is highly significant in various exams like JEE.
The chapter can take 20-25 hours to complete; this session aims to cover it in 1 hour.

Electron (discovered using a discharge tube with a zinc sulfide coating that glowed when struck by particles)
- Particles shown to be negatively charged, hence named electrons.
- Properties:
  - Move in straight lines
  - Create shadows
  - E/M ratio independent of gas nature
  - Charge and mass of electrons known worldwide
Proton (discovered using a modified discharge tube with holes in the cathode)
- Positive particles were named protons.
- Anode rays or canal rays are the terms used for the rays.
- E/M ratio dependent on the nature of the gas used
Neutron (discovered by bombarding beryllium with alpha particles)
- Neutral particle named neutron.
- Relative mass of 1, relative charge is 0

Thompson's Atomic Model
- Compared to a watermelon
- Positively charged sphere with uniformly distributed negative charges (similar to watermelon seeds)
- Known as the watermelon model or plum pudding model
Rutherford's Atomic Model
- Conducted alpha ray scattering experiment using gold foil
- Most alpha particles passed through; some deviated and very few bounced back.
- Concluded that the atom is mostly empty space and has a small, dense, positively charged nucleus.
- Limitations: Could not explain electron distribution or stability per Maxwell's theory

Nature: Comprises oscillating electric and magnetic fields perpendicular to each other and the direction of propagation.
- Can travel through vacuum at the speed of light
- Includes gamma rays, X-rays, UV rays, visible light, IR, microwaves, radio waves
Properties
- Wavelength (λ), Frequency (ν), and Wave Number (ν̄) defined
- Critical formulas: ν = c/λ, E = hν = hc/λ

Black Body Radiation
- Ideal body that can absorb and emit all radiation wavelengths
- Experimentally determined graph: Intensity vs. Wavelength
Photoelectric Effect
- Emission of electrons from metal upon light exposure
- Defined minimum threshold frequency for electron ejection
- Important observations: No time lag, intensity affects number, threshold frequency required, kinetic energy depends on frequency
- Explained by Einstein: hν = hν₀ + KE

Various Series
- Lyman series (UV region), Balmer series (visible region), Paschen, Brackett, Pfund series (IR region)
- Formula for wave number of emitted radiation: ν̄ = RZ²(1/n₁² - 1/n₂²)
Bohr's Atomic Model
- Defined stable orbits for electrons around the nucleus
- Quantization of angular momentum: mvr = n(h/2π)
- Radius, velocity, and energy of electron orbitals formulated
- Limitations: Couldn't explain spectra of multi-electron atoms, Zeeman and Stark effects, or fine structure splitting

De Broglie Hypothesis: Matter has both particle and wave nature
- Formula for wavelength: λ = h/mv or λ = h/√(2mKE)
Heisenberg Uncertainty Principle
- Cannot simultaneously measure position and momentum of particles with absolute certainty.
- ΔxΔp ≥ h/4π
Schrodinger Wave Equation
- Describes electron position using wave functions (Ψ) and probability.
- Probability of finding an electron (Ψ²) determines an orbital's structure.

Aufbau Principle: Electrons occupy lowest energy orbitals first.
Pauli Exclusion Principle: No two electrons can have the same set of four quantum numbers.
Hund's Rule: Degenerate orbitals are singly occupied before pairing.
Notable exceptions: Chromium, Copper showing half-filled and fully-filled stability.

Thorough understanding and review of discovery, properties, models of subatomic particles, nature and behavior of electromagnetic radiation, quantum mechanical models, and electron configurations.
Highlights key principles and exceptions.

Remember: This session covered essential formulas, phenomena, and models necessary for a quick revision of the atomic structure chapter.