Lecture: Structure of Atom (स्ट्रक्चर ऑफ एटम) 🧪

Introduction

• Chapter Importance: The structure of the atom is a very scoring chapter in itself.
• Key Topics: Redox, Orbital
• Electron Placement: Electrons are filled in the increasing order of energy.

Discovery of Subatomic Particles

Discovery of Electron (J.J. Thomson)

1. Experiment: Cathode ray tube experiment
2. Findings: Electron is a negatively charged particle
3. Properties:
   • Travels from cathode to anode
   • Straight-line traveling
   • Independent of gas nature

Discovery of Proton

1. Cathode ray experiment
2. Identification: Anode rays or canal rays
3. Properties:
   • Moves from anode to cathode
   • Positive charge

Discovery of Neutron (James Chadwick)

1. Experiment: Bombardment of Beryllium sheet with alpha particles
2. Findings: Neutral particle (Neutron)
3. Properties: Mass 1.674*10^-27 kg, no charge

Atomic Models

Dalton's Atomic Theory

• Atoms are indivisible.
• Most basic particles of matter

Thomson Atomic Model

• Watermelon model
• Positive charge uniformly distributed
• Limitation: Couldn't explain atomic stability

Rutherford Atomic Model

1. Experiment: Gold foil experiment
2. Observations and Conclusions:
   • Most alpha particles pass without deflection
   • Nucleus is positively charged
   • Atoms are mostly empty space
3. Limitations: Couldn't explain atomic stability

Bohr's Model

1. Postulates: Fixed circular paths, energy levels upon transition
2. Formula: E_n = -13.6 * Z² / n² electron volt
3. Limitations: Multi-electron species, Zeeman, Stark effect

Wave-Particle Duality

De Broglie's Hypothesis

• Wavelength associated with matter: λ = h / mv
• Significance for microscopic particles

Heisenberg Uncertainty Principle

• Δx * Δp ≥ h / 4π
• Importance: The position and velocity of microscopic particles cannot be measured precisely

Quantum Mechanical Model

1. Schrödinger's Equation: Wave-particle solution
2. Quantum Numbers: n, l, m_l, m_s

Quantum Numbers

Principal Quantum Number (n)

• Indicates atomic shell

Azimuthal Quantum Number (l)

• Indicates subshell
• l = 0 (s), 1 (p), 2 (d), 3 (f)

Magnetic Quantum Number (m_l)

• Orientation of orbitals

Spin Quantum Number (m_s)

• Electron spin: +1/2 or -1/2

Atomic Orbitals and Their Shapes

• s-Orbital: Spherical
• p-Orbital: Dumbbell-shaped
• d-Orbital: Double dumbbell

Energy of Atomic Orbitals

• Hydrogen-like Species: Energy depends only on n
• Multi-electron Species: Energy depends on both n and l

Electron Configurations

• Aufbau Principle: Electrons fill in energy order
• Pauli Exclusion Principle: Two electrons in an orbital with opposite spins
• Hund's Rule: Electrons occupy degenerate orbitals singly first.
• Exceptions: Chromium (Cr), Copper (Cu)

Magnetic Properties

• Diamagnetic: No unpaired electron
• Paramagnetic: At least one unpaired electron
• Formula: µ = √(n(n+2)) BM

Conclusion and Important Tips

• Importance of revision
• How to score from the chapter
• Study efficiently and enjoyably

Example Problems and Homework

• Several questions and answers are provided for you to think and solve.