Structure of Atom Lecture Notes

Introduction

• Lecture Series: Mind Map Series
• Topic: Structure of Atom
• Presented by: Rahul (B.Tech from NIT Jaipur)
• Target Audience: Students who have previously studied the chapter

Topics Covered

1. Discovery of Subatomic Particles
2. Atomic Models
   • Thomson's Model
   • Rutherford's Model
3. Dual Nature of Electromagnetic Radiation
4. Quantum Mechanical Model
5. Quantum Numbers
6. Atomic Orbitals and Electronic Configuration

1. Discovery of Subatomic Particles

Electrons

• Discovered by J.J. Thomson using discharge tube experiment
• Key observations:
  • High voltage applied, low pressure inside tube
  • Particles moving towards positive electrode (cathode)
  • Named electrons (negatively charged particles)
  • Charge-to-mass ratio (e/m)
  • Mass ≈ 9.1 x 10^-31 kg

Protons

• Similar experiment but perforated cathode
• Particles moving towards negative electrode (anode)
• Named protons (positively charged particles)
• Charge +1, Mass ≈ 1.672 x 10^-27 kg

Neutrons

• Discovered by bombarding beryllium with alpha particles
• James Chadwick's experiment
• Neutral particles with mass ≈ 1.675 x 10^-27 kg

2. Atomic Models

Thomson's Atomic Model

• Plum pudding model: Electrons embedded in a positively charged sphere

Rutherford's Atomic Model

• Gold foil experiment: Alpha particles bombarded onto gold foil
• Key observations: Most particles passed through, few deflected, very few reflected back
• Conclusions:
  • Atom mostly empty space
  • Mass and positive charge concentrated in a small nucleus
  • Nucleus volume is negligible compared to the atom
• Issues: Did not explain electron distribution and atom's stability

3. Dual Nature of Electromagnetic Radiation

Properties

• Contains electric and magnetic components perpendicular to each other
• Propagates at the speed of light (c) in a vacuum

Electromagnetic Spectrum

• Order by wavelength: Gamma rays, X-rays, UV, Visible, IR, Microwave, Radio waves

Wave and Particle Nature

• Wave properties: Wavelength (λ), frequency (ν), wave number (1/λ)
• Particle properties explained phenomena like black body radiation, photoelectric effect

Planck's Quantum Theory

• Energy emission or absorption in discrete packets (quanta)
• Energy formula: E = hν

Photoelectric Effect

• Electrons ejected from metal surface upon exposure to light of certain frequency
• Threshold frequency required
• Kinetic energy of photoelectrons depends on light's frequency

4. Quantum Mechanical Model

Dual Nature of Matter

• Proposed by De Broglie: Particles exhibit both wave and particle nature
• De Broglie wavelength formula: λ = h/p

Heisenberg's Uncertainty Principle

• Impossible to simultaneously measure exact position and momentum of a particle
• Formula: Δx⋅Δp ≥ h/4π

Schrödinger's Wave Equation

• Describes electron's wave behavior in atoms
• Equation: Incorporates potential and total energy, described by wave function (ψ)

5. Quantum Numbers

Principal Quantum Number (n)

• Indicates energy level and size of the orbital

Azimuthal Quantum Number (l)

• Indicates subshell (s,p,d,f) and shape of the orbital

Magnetic Quantum Number (m_l)

• Indicates orientation of the orbital in space

Spin Quantum Number (m_s)

• Indicates spin direction of the electron (±1/2)

6. Atomic Orbitals and Electronic Configuration

Energy Levels

• For hydrogen-like species, energy depends only on principal quantum number (n)
• For multi-electron atoms, energy uses the n+l rule

Electron Filling Rules

1. Aufbau Principle: Fill lower energy orbitals first
2. Pauli Exclusion Principle: No two electrons can have the same set of quantum numbers
3. Hund's Rule of Maximum Multiplicity: Maximum unpaired electrons with parallel spins before pairing

Special Cases

• Chromium & Copper: Half-filled and fully-filled configurations provide extra stability

Conclusion

• Mind map series is a quick revision tool for students preparing for exams like JEE
• Detailed notes available on the app (Mind Map Series)
• Important to practice consistently and stay positive

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