Discovery of Electron

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Discovery of electron

Two of the founding laws of chemical sciences given by Lavoisier i.e., (laws of chemical combinations, and law of constant proportion) led to upliftment in the discussions on the basic unit of matter from philosophy to science. Dalton who was a school teacher came forward and selected the Greek name atom as the basic unit of matter. He laid a few points to explain the above laws in his theory which is now known as “Dalton’s atomic theory”.

However, the indivisibility of an atom remained a highly controversial point which was also proved wrong later after some of the very famous experiments of the times. Around the twentieth century, many experiments led to the discovery of sub-atomic particles.

Founder of electron

J.J Thomson invented an electron in his model of an atom where he compared the structure of the atom to the Christmas pudding.

The position of the electron was fixed inside the sphere just like the dry fruits in the pudding. Or think of watermelon. The black seeds according to him were like the electrons and the red edible fibrous part of the watermelon is like the positive charge spread throughout the sphere.
He proved the neutrality of the atom by pointing out the fact that protons and electrons of the atom are equal in magnitude.

His theory, like Dalton’s, also came out as faulty and incomplete after a few experiments conducted in the future. J.J Thomson received Nobel Prize in 1906 for his work on the discovery of electrons.

Thomson's model of an atom

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Discovery of electron

Electron invented by J.J Thomson was one of the most important discoveries in the field of chemistry.

Our journey inside the atom started after Michael Faraday pinpointed the relationship of matter with electricity.

1n 1874, Stoney pointed that electricity is made up of discrete units of electricity.

Discharge tube experiments

When electricity is passed through a gas at low pressure inside a glass tube such kinds of experiments are known as discharge tube experiments. These experiments can tell the nature of sub-atomic particles.
These experiments have to be carried at a higher voltage because, at a lower voltage, gases behave as poor conductors of electricity.
J.J Thomson was given the credit to produce electricity through gases under high voltages.

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Electricity flow was observed in the form of rays and these rays were called cathode rays.

The study of these cathode rays led to the discovery of electrons.

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Apparatus for the experiment

1)A cylindrical hard glass tube that is closed from both ends is required, this tube is called a discharge tube.

2)Two electrodes made of metal are fitted inside.

3)A side tube at the side is required through which pressure can be set by evacuation.

4)A vacuum pump.

5)The gas taken for the experiment is filled inside the cathode ray tube.

6)And a high voltage.

Discharge tube

Observations of the experiment

At normal pressure, no observations are made because the gas under the study is poor conductor of electricity. Even at voltages of the order (5,000-10,000 V), no observations are made.
With the help of a vacuum pump, the pressure of the gas is reduced by pumping the gas out.
A decrease of 10^-2 atm is made to make the gas conducting.
This conducting gas then gives a signal by the light of different colors. The color imparted will depend upon the gas taken inside the tube.
However, a further decrease in the pressure will only lead to a weaker glow of the gas. At one point this glow is completely stopped but the conducting nature of the gas remains.
At this point anode side of the tube starts to glow up and the color noticed is greenish light.

Observation of the experiment-

It was concluded that cathode rays were being emitted by the cathode end of the tube. The glow was due to the bombardment of the glass with these rays.
A hole was drilled in the anode to confirm the direction of the movement of these rays. The backside of this hole was coated with zinc sulfide. Zinc sulfide is a fluorescent material so that every time these rays would travel from cathode to anode, a bright spot will emerge on the anode. These cathode rays moved in a straight line from the cathode end of the tube to the anode end of the tube.

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Conclusion of the experiment

Many conclusions were drawn by conducting a few experiments to understand the nature of these cathode rays. Inventor of electron used, application of magnetic field and electric field to confirm the nature of cathode rays.

If an object was kept between the path of cathode rays the casting of shadow will help in the origination of cathode rays. The position of shadow was bent opposite to the wall of the cathode. Flourosense was observed in the region outside the shadow. This shows cathode rays travel in a straight line and these rays travel from cathode to anode.
Since these rays are not visible but these can still be sensed through a fluorescent material that glows up when struck upon.
If a wheel is placed between the electrodes it starts rotating. Meaning that cathode rays show a mechanical effect.
In the absence of a magnetic field and electric field, these rays travel perfectly in a straight line but with the introduction of such a field, these rays show a deflection. This observation shows that cathode rays consist of particles that are charged in nature.
Effect of electric field-To study the effect of electric field the arrangement was modified a bit by the addition of metal plates above and below the tube. When these plates are oppositely charged, cathode rays are preferentially bent to the positively charged plate. This means that the particles of the cathode must be negatively charged.
Effect of magnetic field- In the presence of a magnetic field the cathode rays are deflected in the direction which corresponds to negatively charged particles.

Cathode rays produce a heating effect when struck against a metal foil. Cathode rays also produce X-rays against hard metals.

Charge and mass of an electron- the magnitude of the electron were calculated based on the principle that the greater is the charge on the electron greater will be the interaction of those rays with the magnetic and electric field. the nature and properties of cathode rays are independent of the gas taken in the tube.

The charge to mass ratio is the same for every gas.

The mass of particles depends upon the extent of deviation of that particle. If the mass of the particle will be lighter then its deflection will be greater.
Thomas calculated the mass of electrons by collecting the data from the deflection of the particle.

Electron characteristics

Electrons are discovered by J.J Thomson.

Mass of electron as compared to atom is much smaller.

Therefore, an electron can be defined as the subatomic particle of an atom carrying a unit negative charge (1.6022 × 10^-31C) and the mass of this particle is equal to 9.1 ×10^-31kg.

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NCERT Chemistry Notes:

Frequently Asked Questions (FAQs)

1. Who discovered the electron and when?

J.J Thomson, a high school teacher discovered electrons in the late 19th century.

2. Give characteristics of electron proton and neutron.

Electron is a negatively charged particle carrying a charge of -1.6022 × 10^-31C and a a mass of 9.1 × 10^-31C kg.

The relative charge of an electron is -1.and the relative mass is 5.4858 ×10^-4.

Proton is a positively charged particle carrying a charge of +1.6022 × 10^-31C and a mass of 1.67262 ×10^-27kg.

The relative charge of the proton is +1 and the relative mass is 1.67262 ×10^-27

A neutron is a neutral particle carrying a charge of zero. and a mass of 1.67262 ×10^-27kg.

The relative charge of the neutron is zero and the relative mass is 1.67493 ×10^-27kg.

3. Who named electron?

G. Johnstone Stoney coined the term electron after figured the relationship between electricity and matter.

4. Name the scientist who discovered electrons.

J.J Thomson

5. How was the electron discovered?

Electron was discovered after the discovery of cathode rays which were observed to travel from a straight line and the effect of electric field and magnetic field agreed with the nature of the electron.

6. What led to the discovery of the electron?

The discovery of the electron was primarily led by experiments with cathode ray tubes. Scientists observed that when electricity was passed through gases at low pressure, a beam of particles was emitted from the cathode (negative electrode). These particles were later identified as electrons.

7. Who is credited with discovering the electron?

J.J. Thomson is credited with discovering the electron in 1897. He conducted experiments with cathode ray tubes and concluded that the rays were made up of negatively charged particles, which he initially called "corpuscles" but are now known as electrons.

8. How did J.J. Thomson determine the charge-to-mass ratio of an electron?

Thomson used a cathode ray tube with electric and magnetic fields. By balancing the deflection caused by these fields, he could calculate the charge-to-mass ratio of the particles. This ratio was found to be constant regardless of the gas used or the electrode material, indicating a fundamental particle.

9. How did the discovery of the electron challenge Dalton's atomic theory?

Dalton's atomic theory stated that atoms were indivisible. The discovery of the electron proved that atoms could be further divided into subatomic particles, revolutionizing our understanding of atomic structure.

10. What is the significance of Thomson's cathode ray experiment?

Thomson's cathode ray experiment was significant because it provided the first evidence for the existence of subatomic particles. It showed that atoms were not the fundamental, indivisible units of matter as previously believed, leading to a new era in atomic physics.

11. How did the discovery of the electron impact the field of chemistry?

The discovery of the electron had a profound impact on chemistry. It led to a better understanding of chemical bonding, valence, and the periodic table. It also paved the way for the development of quantum mechanics and modern atomic theory, revolutionizing our understanding of matter and chemical reactions.

12. How did the discovery of the electron lead to the development of the electronic industry?

The discovery of the electron laid the foundation for the electronic industry. Understanding electron behavior led to the development of vacuum tubes, which were used in early radios and computers. This eventually paved the way for transistors, integrated circuits, and modern electronics.

13. How did the discovery of the electron change our understanding of electricity?

The discovery of the electron provided a physical explanation for electricity. It showed that electric current is actually a flow of electrons, rather than an abstract "fluid" as previously thought. This understanding allowed for more precise control and manipulation of electric currents, leading to numerous technological advancements.

14. How did the discovery of the electron contribute to the development of the nuclear model of the atom?

The discovery of the electron suggested that atoms had internal structure, contradicting the idea of atoms as indivisible units. This led scientists to propose new models of the atom, eventually culminating in Rutherford's nuclear model, where negatively charged electrons orbit a small, dense, positively charged nucleus.

15. How did the discovery of the electron influence our understanding of chemical bonding?

The discovery of the electron revolutionized our understanding of chemical bonding. It led to the concept of electron sharing or transfer between atoms, explaining covalent and ionic bonds. This understanding allowed chemists to predict and explain molecular structures and chemical reactions more accurately.

16. What was the "plum pudding" model of the atom?

The "plum pudding" model, proposed by J.J. Thomson, suggested that the atom was a sphere of positive charge with negatively charged electrons embedded in it, like plums in a pudding. This model was an early attempt to explain atomic structure after the discovery of the electron.

17. How did Millikan's oil drop experiment contribute to our understanding of electrons?

Robert Millikan's oil drop experiment, conducted in 1909, allowed for the precise measurement of the charge of an electron. By observing the behavior of charged oil droplets in an electric field, Millikan determined that electric charge always occurred in discrete units, which corresponded to the charge of individual electrons.

18. What is the significance of the electron's negative charge?

The electron's negative charge is fundamental to atomic structure and chemical behavior. It balances the positive charge of protons in the nucleus, allowing for neutral atoms. The attraction between electrons and protons explains atomic stability, while the sharing or transfer of electrons between atoms forms the basis of chemical bonding.

19. What is the relationship between the discovery of the electron and the photoelectric effect?

While the discovery of the electron preceded the explanation of the photoelectric effect, understanding electrons was crucial for Einstein's interpretation. The photoelectric effect, where light causes electron emission from metals, further confirmed the particle nature of electrons and contributed to the development of quantum theory.

20. What is the significance of the electron's wave-particle duality in relation to its discovery?

While the electron was initially discovered as a particle, later experiments revealed its wave-like properties, leading to the concept of wave-particle duality. This duality, a cornerstone of quantum mechanics, shows that the electron (and all matter) can exhibit both wave and particle properties, depending on the experimental setup. This understanding was crucial for developing the modern theory of atomic structure.

21. What is the connection between the discovery of the electron and the development of nuclear magnetic resonance (NMR) spectroscopy?

While the discovery of the electron didn't directly lead to NMR spectroscopy, it was a crucial step in understanding atomic structure. NMR relies on the magnetic properties of certain atomic nuclei, which are influenced by their electronic environment. Understanding electron behavior and its effect on nuclei was essential for developing and interpreting NMR spectroscopy.

22. What is the significance of the electron's spin in relation to its discovery?

While electron spin wasn't discovered until the 1920s, long after the electron itself, it became a crucial property in explaining atomic structure and chemical behavior. Electron spin helps explain the Pauli exclusion principle, magnetism, and fine structure in atomic spectra, significantly enhancing our understanding of electron behavior in atoms and molecules.

23. How did the discovery of the electron influence the development of quantum electrodynamics (QED)?

The discovery of the electron was a crucial step towards quantum electrodynamics. QED, developed in the mid-20th century, describes how light and matter interact, with the electron playing a central role. Understanding the electron's properties and behavior was essential for formulating this theory, which is one of the most precisely tested theories in physics.

24. What role did the discovery of the electron play in explaining the phenomenon of superconductivity?

While superconductivity wasn't discovered until after the electron, understanding electron behavior was crucial for explaining this phenomenon. Superconductivity involves the pairing of electrons (Cooper pairs) at low temperatures, allowing for zero electrical resistance. The discovery of the electron laid the groundwork for understanding such complex electron behaviors in materials.

25. What properties of the electron were determined through early experiments?

Early experiments determined several key properties of the electron, including:

26. What role did vacuum tubes play in the discovery of the electron?

Vacuum tubes, specifically cathode ray tubes, were crucial in the discovery of the electron. These tubes allowed scientists to study the behavior of electrons in a controlled environment, free from interference from gas molecules. The ability to create and manipulate electron beams in these tubes led directly to Thomson's groundbreaking experiments.

27. What was the "Crookes tube" and how was it related to the discovery of the electron?

The Crookes tube, named after Sir William Crookes, was an early type of cathode ray tube. It consisted of a partially evacuated glass tube with metal electrodes. When a high voltage was applied, it produced a beam of electrons (then unknown) that could be observed as a glowing spot on the tube's end. This tube was instrumental in the experiments that led to the discovery of the electron.

28. What evidence suggested that cathode rays were particles rather than waves?

Several pieces of evidence suggested cathode rays were particles:

29. What is the relationship between the discovery of the electron and the concept of isotopes?

While the discovery of the electron didn't directly lead to the concept of isotopes, it was a crucial step. Understanding that atoms contained electrons led to questions about other subatomic particles. The later discovery of the proton and neutron, combined with the known electron, allowed scientists to explain isotopes as atoms with the same number of protons but different numbers of neutrons.

30. What role did spectroscopy play in confirming the existence of electrons?

Spectroscopy played a crucial role in confirming the existence of electrons. The emission and absorption spectra of elements showed discrete lines, which were eventually explained by electrons transitioning between energy levels in atoms. This provided further evidence for the existence and behavior of electrons within atoms.

31. How did the discovery of the electron lead to the development of quantum mechanics?

The discovery of the electron was a crucial step towards quantum mechanics. As scientists tried to explain the behavior of electrons in atoms, classical physics fell short. This led to the development of quantum mechanics to describe the wave-like nature of electrons and their behavior at the atomic scale.

32. How did the discovery of the electron impact our understanding of radioactivity?

The discovery of the electron helped explain certain types of radioactivity. Beta radiation was identified as high-energy electrons emitted from nuclei. This understanding contributed to the broader field of nuclear physics and helped explain how some unstable atoms transform into other elements.

33. What is the historical significance of Thomson's "cathode ray" terminology?

Thomson's use of "cathode ray" terminology reflects the initial uncertainty about the nature of these emissions. While we now know these rays are streams of electrons, the term "cathode ray" persisted, highlighting the historical progression of scientific understanding from an unknown phenomenon to a well-defined particle.

34. How did the discovery of the electron contribute to the development of the periodic table?

The discovery of the electron helped explain the periodic trends observed in the periodic table. The arrangement of elements based on atomic number (number of protons, which equals the number of electrons in a neutral atom) provided a theoretical basis for the periodicity of chemical properties, based on electron configurations.

35. How did the discovery of the electron influence the development of atomic clocks?

The discovery of the electron laid the groundwork for understanding atomic structure and electron energy levels. This knowledge was crucial for the development of atomic clocks, which use the precise frequency of electron transitions in atoms (usually cesium) to measure time with extreme accuracy.

36. What role did the discovery of the electron play in the development of mass spectrometry?

The discovery of the electron was fundamental to the development of mass spectrometry. Understanding how charged particles (ions) behave in electric and magnetic fields, as demonstrated in early electron experiments, formed the basis for mass spectrometers, which separate ions based on their mass-to-charge ratio.

37. How did the discovery of the electron contribute to our understanding of chemical reactions?

The discovery of the electron provided a mechanism for understanding chemical reactions at the atomic level. It showed that many reactions involve the transfer or sharing of electrons between atoms, explaining the formation and breaking of chemical bonds. This led to a more precise understanding of reaction mechanisms and energetics.

38. What is the connection between the discovery of the electron and the development of semiconductor technology?

The discovery of the electron was crucial for the development of semiconductor technology. Understanding electron behavior in materials led to the concept of electron bands in solids, which explains the electrical properties of semiconductors. This knowledge was essential for the invention of transistors and the subsequent development of modern electronics.

39. How did the discovery of the electron influence our understanding of electrical conductivity in materials?

The discovery of the electron provided a physical basis for understanding electrical conductivity. It showed that the flow of electrons through a material constitutes an electric current. This led to the classification of materials as conductors, insulators, and semiconductors based on their electron behavior, revolutionizing materials science and electronics.

40. What impact did the discovery of the electron have on the field of spectroscopy?

The discovery of the electron greatly advanced the field of spectroscopy. It provided a physical explanation for atomic spectra, showing that the discrete spectral lines were due to electrons transitioning between energy levels in atoms. This led to more sophisticated spectroscopic techniques and a deeper understanding of atomic and molecular structure.

41. How did the discovery of the electron contribute to the development of the quantum model of the atom?

The discovery of the electron was a crucial step towards the quantum model of the atom. It led to questions about how electrons were arranged in atoms, which classical physics couldn't answer. This prompted the development of quantum mechanics to explain electron behavior, resulting in the modern quantum model of the atom with electron orbitals and energy levels.

42. What role did the discovery of the electron play in explaining the phenomenon of ionization?

The discovery of the electron provided a clear explanation for ionization. It showed that ions form when atoms gain or lose electrons, rather than some mysterious "electrical fluid." This understanding was crucial for explaining many chemical and physical phenomena, from the formation of ionic compounds to the behavior of plasmas.

43. How did the discovery of the electron influence our understanding of redox reactions?

The discovery of the electron provided a fundamental understanding of redox (reduction-oxidation) reactions. It showed that these reactions involve the transfer of electrons between species. Oxidation could be understood as the loss of electrons, while reduction as the gain of electrons, providing a clear framework for understanding a wide range of chemical processes.

44. How did the discovery of the electron contribute to the development of electron microscopy?

The discovery and understanding of electrons were fundamental to the development of electron microscopy. By using beams of electrons instead of light, electron microscopes can achieve much higher magnification and resolution than optical microscopes. This technology has revolutionized many fields, including materials science and biology.

45. What is the relationship between the discovery of the electron and the development of particle accelerators?

The discovery of the electron and the subsequent understanding of its behavior in electric and magnetic fields laid the groundwork for particle accelerators. These machines use electromagnetic fields to accelerate charged particles (including electrons) to high speeds, allowing for the study of subatomic particles and high-energy physics.

46. How did the discovery of the electron influence our understanding of chemical stability and reactivity?

The discovery of the electron provided insights into chemical stability and reactivity. It led to the octet rule and the concept of valence electrons, explaining why some elements are more reactive than others. Understanding electron configurations helped predict how atoms would combine to form molecules and compounds.

47. What role did the discovery of the electron play in the development of quantum chemistry?

The discovery of the electron was crucial for the development of quantum chemistry. As scientists sought to explain chemical bonding and molecular structure in terms of electron behavior, they had to apply quantum mechanical principles. This led to the field of quantum chemistry, which uses quantum theory to explain and predict chemical phenomena.

48. How did the discovery of the electron contribute to our understanding of magnetism?

The discovery of the electron provided a microscopic explanation for magnetism. It showed that magnetic properties arise from the motion and spin of electrons in atoms. This understanding led to the classification of materials as diamagnetic, paramagnetic, or ferromagnetic based on their electron configurations, revolutionizing the field of magnetism.

49. How did the discovery of the electron influence our understanding of chemical periodicity?

The discovery of the electron provided a physical basis for chemical periodicity. It showed that the periodic trends in elemental properties are due to the arrangement of electrons in atoms. The concept of electron shells and subshells explained why elements in the same group have similar properties, revolutionizing our understanding of the periodic table.

50. What role did the discovery of the electron play in the development of X-ray crystallography?

The discovery of the electron was crucial for understanding X-ray crystallography. X-rays are produced when high-energy electrons interact with matter, and they are diffracted by the electrons in crystalline solids. Understanding the behavior of electrons was essential for interpreting X-ray diffraction patterns and determining crystal structures.

51. How did the discovery of the electron contribute to our understanding of chemical bonding theories?

The discovery of the electron was fundamental to developing chemical bonding theories. It led to the concept of electron sharing in covalent bonds and electron transfer in ionic bonds. Later, it contributed to more advanced theories like valence bond theory and molecular orbital theory, which explain bonding in terms of electron behavior and quantum mechanics.

52. How did the discovery of the electron contribute to our understanding of chemical catalysis?

The discovery of the electron was fundamental to understanding catalysis at the molecular level. Many catalytic processes involve the transfer or sharing of electrons between the catalyst and reactants. Understanding electron behavior in atoms and molecules has allowed chemists to design and optimize catalysts for various chemical reactions.

53. What is the relationship between the discovery of the electron and the development of electron paramagnetic resonance (EPR) spectroscopy?

The discovery of the electron was crucial for the later development of EPR spectroscopy. EPR detects unpaired electrons in materials, providing information about molecular structure and dynamics. Understanding the magnetic properties of electrons, which stem from their spin, was essential for developing and interpreting EPR spectroscopy.