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What did J.J. Thomson's cathode ray experiments demonstrate about atoms?
What did J.J. Thomson's cathode ray experiments demonstrate about atoms?
- Atoms contain negatively charged particles. (correct)
- Atoms are indivisible particles.
- Atoms have no internal structure.
- Atoms are composed only of protons and neutrons.
What is a characteristic of Rutherford's gold foil experiment?
What is a characteristic of Rutherford's gold foil experiment?
- It showed the existence of a positively charged nucleus. (correct)
- It indicated that atoms are completely filled with matter.
- It demonstrated that atoms are solid spheres.
- It confirmed that electrons are embedded in a positive medium.
Which model did J.J. Thomson propose based on his experiments?
Which model did J.J. Thomson propose based on his experiments?
- The planetary model.
- The solid sphere model.
- The quantum model.
- The plum pudding model. (correct)
How did Dalton's atomic theory contribute to modern atomic theory?
How did Dalton's atomic theory contribute to modern atomic theory?
What happens to the cathode ray in a cathode ray tube when it encounters a negatively charged plate?
What happens to the cathode ray in a cathode ray tube when it encounters a negatively charged plate?
What incorrect assumption did Dalton make about atoms?
What incorrect assumption did Dalton make about atoms?
What role do phosphors play in a cathode ray tube?
What role do phosphors play in a cathode ray tube?
According to Rutherford’s findings, what is a significant characteristic of atomic structure?
According to Rutherford’s findings, what is a significant characteristic of atomic structure?
What did Thomson's experiments with cathode rays demonstrate about the charge of the particles?
What did Thomson's experiments with cathode rays demonstrate about the charge of the particles?
Why did Thomson conclude that electrons are a part of all atoms?
Why did Thomson conclude that electrons are a part of all atoms?
What was the approximate mass of the particles compared to a hydrogen atom?
What was the approximate mass of the particles compared to a hydrogen atom?
What led to the need for an entirely new atomic model after Thomson's discoveries?
What led to the need for an entirely new atomic model after Thomson's discoveries?
What model did Thomson propose to explain the structure of the atom?
What model did Thomson propose to explain the structure of the atom?
How did external magnetic fields affect Thomson's experiments?
How did external magnetic fields affect Thomson's experiments?
What conclusion did Thomson draw regarding the nature of charge in an atom?
What conclusion did Thomson draw regarding the nature of charge in an atom?
What was Thomson's method for determining the mass-to-charge ratio of during his experiments?
What was Thomson's method for determining the mass-to-charge ratio of during his experiments?
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Study Notes
J.J. Thomson and the Discovery of the Electron
- J.J. Thomson experimented with cathode ray tubes, which are sealed glass tubes with most of the air evacuated.
- A high voltage is applied across two electrodes, causing a beam of particles to flow from the cathode (negatively charged) to the anode (positively charged).
- The beam of particles is called a "cathode ray" because it originates at the cathode.
- Thomson placed charged electric plates around the cathode ray and observed that the ray was deflected away from the negatively charged plate and towards the positively charged plate.
- This indicated that the cathode ray was composed of negatively charged particles.
- Thomson also placed magnets on either side of the tube and observed that the magnetic field deflected the cathode ray.
- The results of these experiments allowed Thomson to determine the mass-to-charge ratio of the cathode ray particles.
- This led to the discovery that the mass of each particle was much smaller than that of any known atom.
- Thomson repeated his experiments using different metals as electrode materials and found that the properties of the cathode ray remained constant.
- This led Thomson to conclude that the negatively charged particles are a fundamental part of all atoms.
- These subatomic particles were later named "electrons."
The Plum Pudding Model
- Thomson knew that atoms had an overall neutral charge.
- To explain the balanced charge, he proposed that atoms could be described as negatively charged electrons embedded within a soup of diffuse positive charge.
- This model is often referred to as the "plum pudding model."
- This model was groundbreaking as it disproved the part of Dalton's atomic theory that assumed atoms were indivisible.
Rutherford's Gold Foil Experiment
- Ernest Rutherford's gold foil experiment used a beam of alpha particles (positively charged particles) to bombard a thin sheet of gold foil.
- Most of the alpha particles passed through the foil undeflected, but a small number were deflected at large angles.
- This led Rutherford to propose the nuclear model of the atom.
- This model states that the atom is mostly empty space, with a tiny, dense, positively charged nucleus at the center.
- Rutherford proposed that the electrons orbit the nucleus.
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