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Discovery of the Electron

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Discovery of the Electron

Electrons are particles of the atom, just as atoms are substructures of matter. Some of the basic features of atoms were revealed through the experiments that were used in the discovery of the electron. Since the electron was the first subatomic particle discovered, it is seen as one of the turning points in physics. In today's chemistry and physics, it turned out to be one of the most important ones for explaining the chemical bond.

JJ Thomson and the discovery of the electron

Gas discharge tubes today are mostly called cathode-ray tubes because the rays originate at the cathode. Even though other scientists experimented with cathode-ray tubes, JJ Thomson improved and expanded the scope of experiments. With both magnetic and electric fields, he confirmed the negative charge of cathode rays.

He also used a metal cup to catch the rays and discovered an overabundance of negative charge. Thomson was also able to determine the charge of the electron in relation to its mass, qe / me, which was a crucial step in determining the exact values of both qe and me.

Discovery of the Electron, A cathode-ray tube, StudySmarterA cathode ray tube. flickr.com

Elements of the electron discovery process

The elements of the electron discovery process were: the discovery of the electrons, the plum pudding model, Ernest Rutherford, and the gold foil experiment, and the Millikan oil-drop experiment. These steps are important not just because of the discovery of the electron but also because they shape the electron model we have today.

Discovery of the electrons and the plum pudding model

In addition to discovering electrons by experimenting with cathode-ray tubes, JJ Thomson also studied positively charged particles in neon gas. Thomson discovered that the conventional atom model failed to account for negatively and positively charged particles. As a result, he presented a plum pudding model of the atom. In this model, he claimed that:

  • The raisins in the pudding were represented by negative electrons, while the positive charge was held by the dough.

  • All atoms include electrons , which are small negatively charged subatomic particles.

  • Negative particles are floating around in a positively charged soup in an atom.

  • Atoms have an overall neutral charge .

Discovery of the Electron, Plum pudding model of the atom, StudySmarterJJ Thomson's plum pudding model of the atom, Tezcan - StudySmarter Originals

Discovery of the electron: Ernest Rutherford and the gold foil experiment

In 1909 Rutherford carried out the gold foil experiment in which he discovered the nuclear nature of atoms by deflecting alpha particles through a thin gold foil. Rutherford's idea was to look for alpha particles with very high deflection angles, angles that were not expected from any theory of matter at the time.

Hans Geiger and Ernest Marsden conducted the experiment in 1909, directing an alpha-particle (helium nuclei) beam towards thin gold foil and then measuring the angle of Rutherford's scattered alpha particles as a consequence of these particles scattering off gold foil atoms.

They utilized an alpha particle detector that produced fluorescent light spots when alpha particles struck it. The experiment included radon, radium, and bismuth alpha particle emitters.

These deflections could only happen if a large portion of the positive charge was located at the nucleus. It was the data he collected from this experiment that led him to his atomic model in which he claimed that:

  • Atoms are mostly empty space, with the positive charge highly located in the center: the nucleus.
  • The nucleus contains the bulk of the atomic mass.
  • The nucleus has lighter and negatively charged electrons around it.

Discovery of the Electron, Ernest Rutherford working on his experiment, StudySmarterErnest Rutherford at McGill University in 1905, working on his experiment. flickr.com

Discovery of the electron: Millikan oil-drop experiment

The Millikan oil drop experiment by Robert Millikan took place in 1909. It resulted in the first precise direct measurement of a single electron's charge, one of nature's most fundamental constants. In his experiment, he saw that when fine oil drops are sprayed, they get charged.

The charge on a drop may be calculated using the balance of gravity and electric forces. The charge is discovered to be quantized in units of −1.6 * 10 ^ −19 C allowing the charge of the excess and missing electrons on the oil droplets to be determined directly.

Discovery of the electron - key takeaways

  • In 1897 JJ Thomson discovered the electron by using cathode-ray tubes.
  • Three big experiments that helped shape the electron and the atom concept that we have today are the discovery of the electron and the plum pudding model, Rutherford's gold foil experiment, and the Millikan oil-drop experiment.
  • The gold foil experiment is one of the most important experiments since it led to the discovery of the nucleus.
  • Millikan's oil-drop experiment resulted in the first precise direct measurement of a single electron's charge.
  • The discovery of the electron is a turning point in physics because it was the first subatomic particle discovered. It turned out to be the most crucial for describing the chemical bond in today's physics.

Frequently Asked Questions about Discovery of the Electron

 J.J. Thomson discovered the electron. With both magnetic and electric fields, he confirmed the negative charge of cathode rays. He also used a metal cup to catch the rays and discovered an overabundance of negative charge.

The discovery of the electron, and the application of electron ideas to gas discharges, radioactivity, spectroscopy, and atomic structure, ushered in a period of fast progress in physical research that led to today's understanding of atomic structure and chemistry.

The electron was discovered in October 1897.

Final Discovery of the Electron Quiz

Question

Did the plum pudding model say atoms have a neutral total charge?

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Answer

Yes, it did.

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Were cathode-ray tubes used in Thomson's experiment?


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Yes

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What is the concept of the plum pudding model?


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 Negative particles are floating around in a positively charged soup in an atom.

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Who did the gold foil experiment?


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Answer

Ernest Rutherford.

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When did the gold foil experiment take place?


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 In 1909.

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What was the big discovery of the gold foil experiment?


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 The nucleus

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Does the nucleus contain the bulk of the atomic mass?


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Yes, it does.

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Who did the oil drop experiment?


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Answer

Robert Millikan.

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Were electrons the first subatomic particles that were discovered?


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Answer

Yes, they were.

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Was Thomson able to determine the charge of the electron in relation to its mass?

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 Yes.

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What else did Thomson study?

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Answer

Positively charged particles in neon gas.

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 In the plum pudding model, what were the raisins representing?


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Answer

Electrons

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In the plum pudding model, what was the dough representing?

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Answer

Positive charge

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What was Rutherford looking for in his experiment?


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Alpha particles with high deflection angles.

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When did the Millikan oil-drop experiment take place?


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In 1909.

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What was the big discovery of the oil-drop experiment?


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Answer

 First precise direct measurement of a single electron's charge.

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Can the charge on a drop be calculated using the balance of gravity and electric forces?


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Yes, it can.

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The charge of an electron discovered may be quantised in units of what?


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Answer

1.602176634 × 10 ^−19 coulomb.

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Which of the following is not one of the three big steps that helped understand electrons better?


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Answer

Michelson-Morley experiment

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Which of the following describes the setup for the oil-drop experiment?

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Answer

Two horizontal plates with an insulating material with four holes separating the plates.

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Which of the following can be used as an alternative to charging the oil drops in the oil-drop experiment?

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Answer

An x-ray tube.

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Where was the oil sprayed in the oil-drop experiment?

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Answer

Into a chamber above the plates.

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How did Millikan determine the mass of a drop in the oil-drop experiment?

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By examining how quickly the drop falls.

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Which of the following is the first step of the oil-drop experiment?

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While the electric field was turned off, the oil drops were introduced between the plates.

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What is the symbol of the gravitational constant?

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Answer

g.

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What is the unit of the electric field?

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Answer

Newtons/Coulomb.

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What is the value of the charge of a single electron?

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Answer

-1.60 * 10 ^ -19 C.

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E is the symbol of which quantity?

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Electrical field.

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Did Millikan prove the theory of the photoelectric effect?

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Yes, he did.

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All charges were multiples of the fundamental electron charge. True or false?

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Answer

True.

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What is the value of the gravitational constant (g) at the earth's surface?

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Answer

9.8 m / s ^ 2.

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In the situation where the force of gravity on an oil drop equals the force of the electric field surrounding the drop, at which velocity is the drop falling?

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Answer

At its terminal velocity.

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What can alternatively be used to charge the oil drops in the oil-drop experiment other than the friction of the nozzle?

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Answer

An x-ray tube.

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Which of the following is the specific charge of an electron?

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Answer

-1.60*10-19 [C]

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Which of the following experiments resulted in determining the specific charge of an electron?

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Answer

Millikan's experiment.

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 In Millikan's experiment, why was oil chosen instead of water?


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Because it does not evaporate quickly and hence maintains a consistent mass.

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Which of the following is the symbol for the specific charge of an electron?


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Answer

 q.

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Which of the following happens to the selected suitable drop in Millikan's experiment, when the voltage is turned off?

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Answer

The drop drops at its terminal velocity.

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What is the unit of electric field?


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Answer

 [Newtons / Coulombs].

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Electrons were the first subatomic particles to be discovered. True or false?


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Answer

True.

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Question

What is the specific charge of an electron?


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Answer

 -1.60 * 10-19 [C].

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Question

Was JJ Thomson able to determine the specific charge of an electron?


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Answer

No.

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What did JJ Thomson call the negatively charged particles?


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Answer

Corpuscles.

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Who conducted the oil-drop experiment?


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Answer

 Robert Millikan and Harvey Fletcher.

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What was the purpose of the oil drop experiment?


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Answer

 Determining a single electron's specific charge.

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 How did the oil drops become charged in Millikan's experiment?


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Answer

Friction with the nozzle, and alternatively a source of ionising radiation.

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When did the oil drop experiment take place?


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Answer

 In 1909.

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Question

Which of the following is not one of the names for cathode ray tubes?

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Answer

Test tubes.

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Question

Which of the following makes the route of the electrons possible in a cathode ray tube?

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Answer

Electrons exciting the gas atoms, leading to the emission of electromagnetic radiation.

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Question

Which of the following was J.J. Thomson able to determine as a result of his experiments?


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Answer

The ratio between an electron’s charge and its mass.

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