J.J. Thomson and the Electron Discovery

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Questions and Answers

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?

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?

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?

It established foundational postulates about atoms. Signup and view all the answers

What happens to the cathode ray in a cathode ray tube when it encounters a negatively charged plate?

It is deflected away from the plate. Signup and view all the answers

What incorrect assumption did Dalton make about atoms?

Atoms are the smallest units of matter. Signup and view all the answers

What role do phosphors play in a cathode ray tube?

They detect the cathode ray. Signup and view all the answers

According to Rutherford’s findings, what is a significant characteristic of atomic structure?

Atoms are mostly empty space with a dense nucleus. Signup and view all the answers

What did Thomson's experiments with cathode rays demonstrate about the charge of the particles?

The particles were negatively charged. Signup and view all the answers

Why did Thomson conclude that electrons are a part of all atoms?

The same particles were emitted regardless of cathode material. Signup and view all the answers

What was the approximate mass of the particles compared to a hydrogen atom?

Around $rac{1}{2000}$ of the mass of a hydrogen atom. Signup and view all the answers

What led to the need for an entirely new atomic model after Thomson's discoveries?

Thomson's findings contradicted Dalton's atomic theory of indivisibility. Signup and view all the answers

What model did Thomson propose to explain the structure of the atom?

The plum pudding model. Signup and view all the answers

How did external magnetic fields affect Thomson's experiments?

The magnetic fields further deflected the cathode rays. Signup and view all the answers

What conclusion did Thomson draw regarding the nature of charge in an atom?

Atoms have an overall neutral charge due to positive and negative components. Signup and view all the answers

What was Thomson's method for determining the mass-to-charge ratio of during his experiments?

Measuring the deflection of the rays in electric and magnetic fields. Signup and view all the answers

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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Description

Explore the groundbreaking experiments of J.J. Thomson that led to the discovery of the electron. Learn how cathode rays were tested and analyzed, resulting in the identification of negatively charged particles. This quiz delves into Thomson's methodology and the implications of his findings in the field of physics.