What are Electrons: Overview, Questions, Preparation

An electron is a negatively (-1) charged particle. The magnitude of protons and electrons is the same, but electrons contain an opposite sign. However, the molecular weight and size of electrons and protons differ from each other. That is why neutral atoms or compounds have an equal number of electron atoms and proton atoms/molecules. In physics, electrons play an essential role in concepts like electricity, thermal conductivity, magnetism, etc. This role can further be extended to electromagnetic and weak interactions.

Electrons have a circular field that surrounds the outside (outer surface) of an electron. If an electron is in a relative field to that of an observer, the person can observe the electron’s magnetic field.

The electron was identified by the Physicist named J.J.Thompson with John S. Townsend and H.A.Wilson in 1897 while experimenting on cathode rays.

This model has many names like plum pudding, watermelon, etc. It looks like a watermelon containing a positive charge with plums (electrons) in it.

R.A.Millikan did the oil drop experiment to find out the charge on the electrons. He determined an equation on an electron’s charge, which is – 1.6 × 10–19 C. The current acceptable value is – 1.6022 × 10–19 C.

By combining this theory with J.J.Thompson, a mass of an electron was determined, which is shown below:

1. Electrons possess a negative charge.
2. Within an atom, they form an outer shell and stay there in the magnetic field.
3. The symbol of an electron is ‘e−’.
4. The molecular mass of an electron is 1/2000 times compared with the mass of hydrogen tom.
5. The nucleus has a positive charge in the outer shell.
6. When compared to a proton, the molecular mass of an electron is 1/1837 times.
7. The negative charge of an electron is equal to 1.602 × 10-19 coulomb in magnitude.

For the year 2021, as per the new pattern, the chapter structure of atoms holds a weightage of 6 marks, including 3 questions (one short, one very short, and one objective type question).

1. Write the three electron rules used when assigning electrons to orbitals.

Answer: The rules used in assigning electrons to orbitals are as follows:

• The Aufbau principle
• The Pauli-Exclusion principle
• Hund’s Rule

2. Write the absolute charge of an electron.

Answer: The absolute charge of an electron is -1.6022 x 10^-31.

3. Illustrate the cathode rays with the help of a diagram.

Answer: Cathode ray tube is made up of electrodes, which are two thin pieces of metal. Through evacuation, the pressure of different gases can be increased or decreased as per the requirements. When sufficient force is passed through the electrodes, the current passes to the positive charge (anode) from the negative charge (cathode). The diagram of the cathode ray discharge tube is illustrated below - 

[Image courtesy: NCERT]