1.3.2 The discovery of the electron, nucleus, and proton

• What did Thomson's cathode ray experiment prove?

  It proved that electrons exist
• If the radius of the circular path of the α-particles is $r$, what is the formula to calculate the centripetal force acting on the α-particle?


  $F_c =$$\frac{mv^2}{r}$
• What is the purpose of the thin gold foil shown in the image?

  • The thin gold foil is used to allow the α-particles to pass through and be detected by the device.
• What does the plum pudding model propose about atoms?

  Atoms are like a bun with positive charge
• What is the name of the positively charged matter shown in the image?

  Positively charged matter
• What conclusion did Rutherford draw about the structure of an atom?

  Most of an atom is empty space
• How are the electrons arranged in the image?

  • The electrons are arranged in a spherical pattern around the positively charged matter
  • The electrons are evenly distributed around the positively charged matter
• How does the detector in the image work to detect the α-particles?

  • The detector measures the deflection of the α-particles as they pass through the thin gold foil, providing information about their charge and mass.
• What charge do protons have?

  Positive (+)
• What type of particles were used in Rutherford's experiment?

  Alpha particles
• What does it mean that most balls went right through the castle?

  Atoms are mostly empty inside
• What is the name of the model shown in the image?

  Nuclear model
• What type of particles were fired at the gold foil in Rutherford's experiment?

  Alpha particles
• How did Rutherford's model of the atom differ from Thomson's "plum pudding" model?

  Rutherford's model suggested atoms have a dense core surrounded by empty space, unlike Thomson's model which had a uniform distribution of positive and negative charges
• What were the main conclusions of Rutherford's gold foil experiment?

  • Atoms are mostly empty inside
  • There is a tiny, strong center called the nucleus
• What analogy is used to describe the discovery of the nucleus?

  Like discovering the sun in our solar system
• Where do electrons orbit in an atom?

  Electrons orbit the nucleus
• What did Rutherford's gold foil experiment suggest about the structure of an atom?

  • Most of an atom is empty space
  • Positive charge is concentrated in a tiny central area (the nucleus)
  • Electrons must orbit at a distance from the nucleus
• What is the purpose of the lead block shown in the image?

  • The lead block is used to emit the α-particles that are detected by the device.
• What are the small spheres in the image?

  Electrons
• What is the nucleus of an atom?

  The tiny center where mass is concentrated
• What did the new understanding of atoms help scientists understand better?

  Nuclear reactions and energy sources
• What does the discovery of the electron represent in atomic structure?

  A fundamental particle of atoms
• What particles were discovered that changed atomic theory?

  Electron, nucleus, and proton
• Where are protons located in an atom?

  In the nucleus
• How did Rutherford's experiment change the understanding of atomic structure?

  It showed positive charge is concentrated centrally
• What is the name of the particle shown flowing through the device?

  α-particle
• What are the two models of the atom mentioned?

  Nuclear model and quantum model
• Who discovered the electron?

  J.J. Thomson
• What does the discovery of smaller particles inside atoms indicate?

  Atoms consist of smaller particles
• 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 physics experiments
• How does the mass of an electron compare to an atom?

  Very small
• What did Thomson observe about the rays in his experiment?

  They were deflected toward the positive plate
• What did Rutherford use in his gold foil experiment?

  Alpha balls and a gold castle
• How does the mass of electrons compare to protons?

  Electrons are very light
• What is the name of the tiny, strong wall inside the atom?

  Nucleus
• What does it mean if very few balls bounced right back?

  There is a tiny, strong wall inside
• What was the target material in Rutherford's gold foil experiment?

  Thin gold foil
• What were the three main observations from Rutherford's gold foil experiment?

  1. Most particles passed straight through, 2. Some were deflected slightly, 3. Very few bounced back
• What experiment did Thomson conduct to support his model?

  Cathode ray experiment