Electrons

As a fundamental particle, the electron is indivisible and is one of the building blocks of matter. It is classified as a lepton, a category of particles that do not experience the strong nuclear force but do participate in weak nuclear interactions and electromagnetic interactions.

1.0Discovery of Electron

Michael Faraday (1830): 

Faraday's experiments with electrolysis showed that electricity passing through an electrolyte causes chemical reactions at the electrodes, indicating the particulate nature of electricity. This laid the groundwork for understanding the behavior of charged particles.

Cathode Ray Experiments

Mid-1850s Studies: Scientists, including Faraday, began studying electrical discharges in partially evacuated tubes, known as cathode ray tubes (CRTs).

Here is a brief introduction about Cathod ray experiments:

• A CRT is a glass tube containing two electrodes (metal pieces) and is used to study electrical discharges at low pressures and high voltages.
• When high voltage is applied, a stream of particles (cathode rays) moves from the cathode (negative electrode) to the anode (positive electrode).

Observation: 

The flow of cathode rays can be detected by making a hole in the anode and coating the area behind it with fluorescent or phosphorescent material like zinc sulfide. When cathode rays strike the coating, a bright spot is formed.

Cathode rays move from the cathode to the anode and are invisible but detectable by their effect on fluorescent materials. They travel in straight lines without fields and behave like negatively charged particles in electric or magnetic fields, indicating they are electrons.

Conclusion

• Negatively Charged Particles- The experiments concluded that cathode rays consist of negatively charged particles, later named electrons.

Read more: Cathode Ray Experiment

2.0Properties of Electron

Property	Description
Charge	Electrons have a negative electric charge, denoted as −1 or −e, where e is the elementary charge (approximately 1.602×10−19 coulombs).
Mass	The rest mass of an electron is about 9.109×10−31 kilograms, which is approximately 1/1836 the mass of a proton.
Spin

Electrons are fermions with a half-integer spin (1\2), meaning they  obey the Pauli exclusion principle, which states that no two electrons can occupy the same quantum state simultaneously.

3.0Quantum Mechanical Nature of Electron

• Wave-Particle Duality: Electrons exhibit dual characteristics of both waves and particles. This duality is evident in phenomena such as the double-slit experiment, where electrons can form interference patterns, demonstrating their wave-like behavior.
• Wavefunction: In quantum mechanics, the behavior of electrons is described by wavefunctions, which provide the probability distribution of an electron’s position and momentum.

Role of Electron in the Atom:

• Orbitals: Electrons are found in atomic orbitals, which are regions around the nucleus where the probability of finding an electron is highest. These orbitals are arranged in energy levels or shells.
• Electron Configuration: The arrangement of electrons in these orbitals determines an atom's chemical properties and reactivity. This configuration follows principles like the Aufbau principle, Hund's rule, and the Pauli exclusion principle.
• Chemical Bonds: Electrons are key to forming chemical bonds. In covalent bonds, electrons are shared between atoms, while in ionic bonds, electrons are transferred from one atom to another.

Interactions and Forces:

• Electromagnetic Interaction: Electrons interact with other charged particles through the electromagnetic force, which is described by Coulomb's law. This law states that like charges repel each other while opposite charges attract.
• Photon Interaction: Electrons can absorb and emit photons, causing transitions between different energy levels. This interaction is fundamental to processes like fluorescence, phosphorescence, and the emission of light from excited atoms.

Electron Distribution in Orbits:

1. Maximum Electrons per Shell: The maximum number of electrons in a shell is given by the formula 2n², where n is the orbit number.

Example:

• K-shell (n=1): 2 electrons
• L-shell (n=2): 8 electrons
• M-shell (n=3): 18 electrons
• N-shell (n=4): 32 electrons

2. Outer Shell Limitation: The outermost shell can hold a maximum of 8 electrons, regardless of the 2n² rule.
3. Sequential Filling: Electrons fill the inner shells first before moving to the outer shells.

Example :

• Carbon (Atomic Number = 6): Electron distribution: 2,42, 42,4.
• Sodium (Atomic Number = 11): Electron distribution: 2,8,12, 8, 12,8,1.

If the K and L shells are full, the total number of electrons in the atom would be 10.