Electrons - Meaning, Definition, Properties, FAQs

Electron

The electron is a fundamental subatomic particle, represented by the symbol $e^{-}$, and it carries a negative elementary electric charge. Electrons belong to the first generation of the lepton family and, since they have no known internal structure, are considered elementary particles. The magnitude of the electric charge of an electron is equal to that of a proton but opposite in sign. Therefore, an electrically neutral atom or molecule contains an equal number of protons and electrons.

Although the charge of an electron is equal in magnitude to that of a proton, its mass and size are much smaller. The mass of an electron is approximately $1 / 1836$ times that of a proton. Like all elementary particles, electrons exhibit a dual nature, meaning they possess both particle and wave properties. As a result, electrons can collide with other particles like matter and also show wave phenomena such as diffraction, similar to light.

Discovery of Electrons

The electron was discovered in 1897 by the British physicist J. J. Thomson through his experiments on cathode rays using a discharge tube. Thomson observed that when a high voltage was applied across electrodes in a vacuum tube, rays were emitted from the cathode and moved toward the anode. These rays were deflected by electric and magnetic fields, indicating that they consisted of negatively charged particles.

By studying the deflection of cathode rays, J. J. Thomson was able to determine the charge-to-mass ratio (e/m) of the electron. He concluded that these particles were present in all atoms, leading to the discovery of the first subatomic particle, later named the electron.

The Cathode Ray Experiment by Thomson.

The Cathode Ray Experiment, conducted by J. J. Thomson in 1897, led to the discovery of the electron and proved that atoms are not indivisible. Thomson used a discharge tube consisting of two electrodes cathode (negative) and anode (positive) sealed inside a glass tube containing gas at very low pressure.

When a high voltage was applied across the electrodes, rays originated from the cathode and moved toward the anode. These rays were called cathode rays. Thomson observed that cathode rays were deflected by electric and magnetic fields toward the positive plate, indicating that they carried a negative charge. He also found that the properties of cathode rays were independent of the nature of the gas and electrodes, proving that electrons are present in all atoms.

By measuring the deflection of cathode rays, Thomson calculated the charge-to-mass ratio (e/m) of the electron. This experiment confirmed the existence of electrons and marked a major milestone in the development of atomic structure and modern physics.

Charge of Electrons

• A negatively charged particle is an electron. The magnitude of the negative charge is $1.602 \times 10^{-19}$ coulomb.
• An electron has a mass of 1/1837 that of a proton.
• An electron has a mass of $9.10938356 \times 10^{-31}$ kilograms.

Related Topics,

• Atomic number mass number
• Quantum Numbers
• Proton Neutron Discovery
• Anions and cations difference
• Bohrs Model
• Aufbau principle

Properties of Electrons

Quantum particles have their own set of particular qualities that are not shared by other particles. Protons, neutrons, and electrons have well-defined properties for the most part. Here are some of an electron's characteristics:

• The mass of an electron is $9.1 \times 10^{-31}$ kg, which is equal to 0.000548579909 atomic mass units. An electron's mass can also be expressed as 1/1840 of the mass of a hydrogen atom. Because the mass of a hydrogen atom is 1 u, the relative mass of an electron can be written as 1/1840 u.

• An electron's absolute mass is $9 \times 10^{-28}$grams.

• The effective charge of an electron is -1 because an electron is a negatively charged particle.

• Because electrons have a negative charge, the electrical charge should be $1.602 \times 10^{-19}$ coulombs.

• Electrons orbit the nucleus of the atom in particular, well-defined orbits around the element's nucleus.

• The properties of an electron are unaffected by the gas present in the discharge tube and are independent of it.

• Electrons also have a two-sided nature known as wave-particle duality, which implies that under certain conditions, the electrons, which are particles, behave like a wave.

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Some Solved Examples

Question 1: The charge-to-mass ratio $(e / m)$ of an electron was first determined by
A. Millikan
B. Rutherford
C. J. J. Thomson
D. Chadwick

Solution:

J. J. Thomson determined the e/m ratio of the electron using the cathode ray experiment.
Millikan later measured the charge of the electron, not e/m.

Hence, the correct answer is option is (C)

Question 2: Which of the following properties correctly describes an electron?

A. It has positive charge and large mass
B. It has no charge and exists in the nucleus
C. It has negative charge and negligible mass
D. It has variable charge

Solution:

An electron carries a negative charge $\left(-\mathbf{1 . 6 \times 1 0} \mathbf{0 0}^{-\mathbf{1 9}} \mathrm{C}\right)$ and has a very small mass compared to protons and neutrons.

Hence, the correct answer is option is (C)

Question 3: The mass of an electron is approximately

A. Equal to proton mass
B. 1/1000 of proton mass
C. 1/1836 of proton mass
D. Negligible compared to neutron only

Solution:

$m_e \approx \frac{1}{1836} \times m_p$

Hence, the correct answer is option is (C)

Question 4: Which experiment proved the wave nature of electrons?

A. Cathode ray experiment
B. Oil drop experiment
C. Photoelectric effect
D. Davisson–Germer experiment

Solution:

The Davisson–Germer experiment demonstrated electron diffraction, confirming the wave nature of electrons.

Hence, the correct answer is option is (D)