Competitive exam General Science- Chemistry

 

Electrons are subatomic particles with a negative electric charge. Here's a brief overview regarding electrons:

When

• Discovery: The existence of electrons was confirmed by J.J. Thomson in 1897.
• Historical Context: Thomson's experiments with cathode rays led to the discovery of the electron, marking a significant milestone in the field of atomic physics.

What

• Nature: Electrons are fundamental particles, meaning they are not made up of smaller components.
• Charge: They carry a negative charge, denoted as -1 elementary charge.
• Mass: The mass of an electron is approximately 1/1836 that of a proton.
• Role: Electrons play a crucial role in electricity, magnetism, and chemistry. They are involved in forming chemical bonds, conducting electricity, and generating magnetic fields.

Where

• Location in Atoms: Electrons are found in the electron cloud surrounding the nucleus of an atom. This cloud is divided into energy levels or shells where electrons are likely to be found.
• In Nature: Electrons are present in all matter. They are integral components of atoms, and thus, they are found everywhere in the universe where matter exists.
• In Technology: Electrons are harnessed in various technologies, including electronics (transistors, diodes), electric power generation and distribution, and medical devices (X-ray machines, MRI).

Additional Points

• Behaviour: Electrons exhibit both particle-like and wave-like properties, a concept known as wave-particle duality.
• Quantum Mechanics: The behaviour and properties of electrons are described by quantum mechanics, which explains phenomena such as electron orbitals, quantum tunnelling, and entanglement.

 What is the charge of an electron?

• Answer: The charge of an electron is negative, specifically -1 elementary charge.

Who discovered the electron and in what year?

• Answer: The electron was discovered by J.J. Thomson in 1897.

What is the relative mass of an electron compared to a proton?

• Answer: The mass of an electron is approximately 1/1836 that of a proton.

Where are electrons located in an atom?

• Answer: Electrons are located in the electron cloud surrounding the nucleus of an atom.

Describe the role of electrons in chemical bonding.

• Answer: Electrons play a crucial role in chemical bonding by sharing or transferring between atoms to form covalent or ionic bonds, respectively, which stabilizes the atoms involved.

 Explain the concept of electron energy levels or shells.

• Answer: Electron energy levels or shells are specific regions around the nucleus of an atom where electrons are likely to be found. Each energy level can hold a certain number of electrons and corresponds to different energy states.

What is the significance of the electron cloud in the structure of an atom?

• Answer: The electron cloud represents the regions around the nucleus where electrons are most likely to be found. It determines the size and shape of the atom and plays a key role in chemical interactions and bonding.

How do electrons contribute to electrical conductivity in metals?

• Answer: In metals, electrons are free to move throughout the material. These free electrons, or conduction electrons, facilitate the flow of electric current when an external voltage is applied, making metals good conductors of electricity.

Describe the wave-particle duality of electrons.

• Answer: The wave-particle duality of electrons refers to the concept that electrons exhibit both particle-like and wave-like properties. This duality is demonstrated by experiments such as the double-slit experiment, where electrons produce an interference pattern characteristic of waves.

Explain how the behaviour of electrons is described by quantum mechanics.

• Answer: Quantum mechanics describes the behaviour of electrons in terms of probabilities and wave functions. It explains phenomena such as quantized energy levels, orbital shapes, and electron spin, using principles like the Schrödinger equation and Heisenberg Uncertainty Principle.

What is the Pauli Exclusion Principle and how does it apply to electrons in an atom?

• Answer: The Pauli Exclusion Principle states that no two electrons in an atom can have the same set of quantum numbers. This principle explains the unique arrangement of electrons in different orbitals and energy levels, ensuring that each electron occupies a distinct state.

 Describe the process of electron excitation and emission of photons in an atom.

• Answer: When an electron absorbs energy, it can become excited and move to a higher energy level. When the electron returns to its ground state, it releases the absorbed energy as a photon. The energy of the emitted photon corresponds to the difference in energy between the two levels.

How are electrons involved in the generation of electricity in a circuit?

• Answer: Electrons move through conductive materials in a circuit when a voltage is applied, creating an electric current. This flow of electrons is harnessed to perform work, such as lighting a bulb or powering a motor.

Explain how the movement of electrons creates a magnetic field.

• Answer: The movement of electrons, or electric current, generates a magnetic field around the conductor. This phenomenon is described by Ampère's law and is the principle behind electromagnets and many electrical devices.

 Describe the role of electrons in semiconductor devices such as transistors and diodes.

• Answer: In semiconductor devices, electrons and holes (electron deficiencies) control the flow of current. Transistors use electric fields to modulate electron flow, enabling amplification and switching. Diodes allow current to flow in one direction by using a p-n junction, where electrons and holes recombine.

 How are electrons utilized in medical imaging technologies such as X-rays and MRI?

• Answer: In X-rays, high-energy electrons collide with a metal target, producing X-ray photons used for imaging. In MRI, radiofrequency pulses affect the spin states of electrons in hydrogen atoms, generating signals that are used to create detailed images of the body's internal structures.

True/False Questions

1. Electrons have a positive charge.
• Answer: False. Electrons have a negative charge.
2. Electrons are found in the nucleus of an atom.
• Answer: False. Electrons are found in the electron cloud surrounding the nucleus.
3. Electrons have wave-like properties.
• Answer: True. Electrons exhibit wave-like properties as described by wave-particle duality.
4. The mass of an electron is approximately equal to the mass of a neutron.
• Answer: False. The mass of an electron is much smaller than the mass of a neutron.