1.3.2 The discovery of the electron, nucleus, and proton

• What are the key developments in the history of the atomic model?

  • Democritus: Proposed the idea of indivisible atoms
  • Thomson: Proposed the plum pudding model with electrons embedded in a positive sphere
  • Rutherford: Proposed the nuclear model with a dense, positively charged nucleus and orbiting electrons
  • Bohr: Proposed the Bohr model with electrons orbiting the nucleus in discrete energy levels
  • Quantum: Proposed the quantum mechanical model with probability distributions of electrons
• What are the key components of J.J. Thomson's experiment that led to the discovery of the electron?

  • Cathode rays were produced in a vacuum tube
  • Rays were deflected by a magnetic field
  • Deflection indicated a negative charge
  • Named the particles electrons
• What is the purpose of the thin gold foil in the device?

  • The thin gold foil is used to detect the flow of α-particles
  • It allows the α-particles to pass through and be detected
• How could this setup be used to accelerate charged particles?

  • Charged particles (e.g. electrons) would be attracted to the positively charged plate
  • This would accelerate the particles through the electric field between the plates
  • The accelerated particles could then be used for various applications like particle beams
• How did the atomic models evolve over time?

  • Democritus: Indivisible atoms
  • Thomson: Plum pudding model
  • Rutherford: Nuclear model
  • Bohr: Discrete energy levels
  • Quantum: Probability distributions
• What were the three key results of Rutherford's experiment?

  1. Atom mostly empty space
  2. Small, dense central region exists
  3. Positive charge concentrated in center
• What is the name of the particle shown flowing through the device?

  α-particle
• Who first proposed the idea of the atom?

  Democritus
• What is the purpose of the thin gold foil in the device?

  • The thin gold foil is used to detect the flow of α-particles
  • It allows the α-particles to pass through and be detected
• Who discovered cathode rays?

  J.J. Thomson
• What are the key findings of Rutherford's alpha particle experiment regarding atomic structure?

  • Gold foil exhibited a residual positive charge
  • Existence of positively charged particles (protons)
  • Protons define the atomic number
  • Atomic number determines the element identity
• What is the name of the negatively charged metal plate in the image?

  negatively charged metal plate
• What did Rutherford name the positively charged particles he discovered?

  Protons
• Who proposed the nuclear model of the atom?

  Rutherford
• What was the main observation about the alpha particles in Rutherford's experiment?

  Most passed straight through the foil
• What type of particles did Rutherford use in his experiment?

  Alpha particles
• Who discovered the atom?

  Democritus
• How does the lead block in the device function?

  • The lead block shields the detector from external radiation
  • This allows the detector to focus on measuring the α-particles from the radium source
• Who proposed the Bohr model of the atom?

  Bohr
• How does the atomic number determine an element?

  It identifies which element the atom is
• What was the target material in Rutherford's experiment?

  Very thin gold foil
• What is the significance of the central core in the Rutherford model?

  It is a positive core that contains protons
• How does the detector in the device work to detect the α-particles?

  • The detector measures the deflection or scattering of the α-particles as they pass through the thin gold foil
  • This allows the properties of the α-particles to be studied
• What defines an atom's atomic number?

  The number of protons in its nucleus
• What is the purpose of the positively and negatively charged metal plates in the image?

  • The positively charged metal plate attracts electrons
  • The negatively charged metal plate repels electrons
  • Together they create an electric field that can accelerate charged particles
• What is the name of the particle shown flowing through the device?

  α-particle
• What are the key features of the quantum mechanical model of the atom?

  • Electrons exist in probability distributions around the nucleus
  • Electrons can only occupy certain allowed energy levels
  • Quantum numbers (n, l, m, s) describe the electron's state
  • Heisenberg's uncertainty principle - cannot precisely know both position and momentum
• How did J.J. Thomson discover cathode rays?

  By passing electricity through a vacuum tube
• What does the Rutherford model describe about the atom?

  It has a small, dense nucleus
• What is the name of the device shown in the image?

  Detector
• What is the name of the positively charged metal plate in the image?

  positively charged metal plate
• Why did Rutherford reason that positively charged particles existed?

  Due to the residual positive charge observed
• What significant developments occurred in atomic theory over time?

  • Evolution of the concept of the atom
  • Discovery of the dense nucleus
  • Identification of subatomic particles
• How does the lead block in the device function?

  • The lead block shields the detector from external radiation
  • This allows the detector to focus on measuring the α-particles from the radium source
• Whose atomic theory did J.J. Thomson build upon with his discovery?

  Democritus' atomic theory
• Who discovered the nucleus?

  Ernest Rutherford
• Who proposed the plum pudding model of the atom?

  Thomson
• What did Rutherford notice during his alpha particle experiment?

  Gold foil had a residual positive charge
• How did the understanding of the atom change from Democritus to the 20th century?

  It evolved from indivisible particles to complex structures
• How did the Rutherford model revise the solid sphere idea of atoms?

  It showed atoms consist of mostly empty space