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Understanding the Structure of Atoms

Sep 3, 2024

Class 11 Chemistry: Structure of Atom - Lecture Notes

Overview

  • This lecture covers the chapter "Structure of Atom" from Class 11 Chemistry.
  • It is a crucial chapter for competitive exams (NEET, JEE) and provides a deeper understanding of previously learned concepts.
  • Focus on the discovery of subatomic particles, atomic models, and important experiments related to atoms.

Key Topics

  1. Discovery of Subatomic Particles
    • Particles within an atom: Electrons, Protons, Neutrons.
    • These particles determine the characteristics and properties of atoms.
  2. Atomic Models
    • Various models explain the arrangement and behavior of subatomic particles within an atom.
    • Models to be studied:
      • Thomson's Atomic Model
      • Rutherford's Atomic Model
      • Bohr's Atomic Model
      • Quantum Mechanical Model (Accepted model)
  3. Developments Leading to Models
    • Discovery of electromagnetic radiation, atomic and hydrogen spectra.
    • Concepts like Heisenberg's Principle and de Broglie Wave Equation.

Discovery of Electrons

  • Scientist: J.J. Thomson.
  • Experiment: Cathode ray discharge tube.
    • Setup: Glass tube with cathode (negative) and anode (positive) connected to a high voltage battery (~10,000 volts).
    • Observation: Rays (cathode rays) moved from cathode to anode, composed of invisible particles.
    • Characteristics:
      • Travel in straight lines.
      • Negatively charged (deflect towards positive electric/magnetic fields).
      • Properties are independent of the type of gas used.
    • Conclusion: Rays later identified as electrons.

Charge to Mass Ratio of Electron

  • Discovered by: J.J. Thomson.
  • Experiment: Based on the deflection of cathode rays in electric and magnetic fields.
  • Value: Charge/mass ratio = 1.75 x 10^11 C/kg.
  • Factors Affecting Deflection:
    1. Greater charge magnitude = greater deflection.
    2. Stronger electric/magnetic fields = greater deflection.
    3. Lighter mass of particles = more deflection.

Charge and Mass of Electron

  • Charge: Found by Millikan's oil drop experiment.
    • Value: -1.6 x 10^-19 C.
  • Mass: Calculated using charge and charge/mass ratio.
    • Value: 9.1 x 10^-31 kg.

Important Values to Remember

  1. Charge of Electron: -1.6 x 10^-19 C
  2. Mass of Electron: 9.1 x 10^-31 kg
  3. Charge to Mass Ratio: 1.75 x 10^11 C/kg

Summary

  • The lecture elucidated the discovery of electrons, their charge, and mass.
  • Upcoming lectures will cover the discovery of protons and neutrons and include practice questions for competitive exams.

Full transcript