ELECTRON
For understanding the nature of charged particles in matter, let us carry out the following activities:
Activity 4.1:
A. Comb dry hair. Does the comb then attract small pieces of paper?
B. Rub a glass rod with a silk cloth and bring the rod near an inflated balloon. Observe what happens
From these activities, can we conclude that on rubbing two objects together, they become electrically charged? Where does this charge come from? This question can be answered by knowing that an atom is divisible and consists of charged particles.
Many scientists contributed in revealing the presence of charged particles in an atom. It was known by 1900 that the atom was indivisible particle but contained at least one sub-atomic particle – the electron identified by J.J. Thomson.
The mass of an electron is considered to be negligible and its charge is minus one.
Questions
If an atom contains one electron , will it carry any charge or not?
Source: This topic is taken from NCERT TEXTBOOK
PROTON
E. Goldstein in 1886 discovered the presence of new radiations in a gas discharge and called them canal rays. These rays were positively charged radiations which ultimately led to the discovery of another sub-atomic particle. This sub-atomic particle had a charge, equal in magnitude but opposite in sign to that of the electron. Its mass was approximately 2000 times as that of the electron. It was given the name of the proton.
In general, a proton is represented as ‘p+ ’. The mass of a proton is taken as one unit and its charge as plus one.
Questions
What are the canal rays?
Source: This topic is taken from NCERT TEXTBOOK
NEUTRON
A neutron is a sub-atomic particle with no net electrostatic charge, with a very similar mass to a proton. Neutrons are thought to comprise of one up quark of charge +2/3 and two down quarks of charge -1/3 each, resulting in a net charge of zero. Neutrons are present in almost all atomic nuclei except for hydrogen.
The mass of the neutron is 1.6749286 × 10-27 kg.
When neutrons are isolated in space they decay with a half-life of about 15 minutes and decay into a proton, an electron, and an anti-neutrino. This process is known as beta decay, where beta refers to the electron. As a result of this process, space is relatively devoid of free neutrons.
Atoms with the same number of protons in the nucleus, but different numbers of neutrons are referred to as isotopes of the same elements.
The neutron was discovered by Chadwick in the 1930s.
Source: This topic is taken from NCERT TEXTBOOK