Introduction to Structure of Atom
An atom is the smallest unit of matter that retains the properties of an element. It consists of a central nucleus surrounded by electrons. The nucleus contains protons (positively charged) and neutrons (neutral particles), while electrons (negatively charged) revolve around the nucleus in specific energy levels.
Discovery of Subatomic Particles
Initially, atoms were considered indivisible, but later, experiments revealed the presence of subatomic particles:
1. Discovery of Electron
Scientist: J.J. Thomson (1897)
Experiment: Cathode Ray Tube Experiment
Observations:
A beam of negatively charged particles (cathode rays) was emitted from the cathode.
These particles were deflected by electric and magnetic fields.
Conclusion: Electrons are negatively charged subatomic particles.
2. Discovery of Proton
Scientist: E. Goldstein (1886)
Experiment: Canal Ray Experiment
Observations:
A different type of ray (canal rays) was observed moving in the opposite direction of cathode rays.
These rays were positively charged.
Conclusion: Protons are positively charged subatomic particles.
3. Discovery of Neutron
Scientist: James Chadwick (1932)
Experiment: Bombardment of beryllium with alpha particles
Observations:
A new type of neutral radiation was observed.
Conclusion: Neutrons are neutral subatomic particles present in the nucleus.