JOURNEY INSIDE THE ATOM-1

PRERNA FOR IAS

         Mehnat Aapki, Guidance Humari

         Roz ki Prelims Practice — Experts ke Saath

JOURNEY INSIDE THE ATOM-1

1. Early Concept of the Atom (Acharya Kanada and Leucippus–Democritus)

The idea of the atom was proposed long before modern science. In India, Acharya Kanada suggested that matter is made of tiny, indivisible particles called Parmanu, which combine to form all substances. In ancient Greece, Leucippus and Democritus introduced the concept of Atomos, meaning indivisible particles. Although they had no experimental evidence, their ideas laid the foundation for atomic theory. They believed that matter is composed of extremely small particles that cannot be divided further. These philosophical concepts inspired later scientists to study the structure of matter scientifically and develop modern atomic theory.

2. Dalton's Atomic Theory

John Dalton proposed the first scientific atomic theory in 1808, based on experimental observations. According to Dalton, all matter is made of tiny, indivisible particles called atoms. Atoms of the same element are identical in mass and chemical properties, while atoms of different elements differ. He also stated that atoms cannot be created, destroyed, or divided during chemical reactions. Compounds are formed when atoms combine in simple whole-number ratios. Dalton's theory explained many chemical laws and became the foundation of modern chemistry. Although some postulates were later modified, his theory revolutionized the scientific understanding of matter.

3. J. J. Thomson's Cathode Ray Experiment

In 1897, J. J. Thomson performed the cathode ray tube experiment, which led to the discovery of the electron. He used a glass tube containing a cathode and an anode under low pressure and applied high voltage. Rays emitted from the cathode travelled toward the anode and were deflected by electric and magnetic fields, proving they carried negative charge. Thomson concluded that these rays consisted of tiny negatively charged particles called electrons, which are present in all atoms. This experiment proved that atoms are divisible and contain smaller particles, changing the understanding of atomic structure forever.

4. Discovery of the Electron and Its Significance