Hydrogen Spectrum || STRUCTURE OF ATOM ||L#10 ||NEET/JEE/11th|| Dr A K Singh

Telegram Channel Link :- https://t.me/DrAmodkrsingh
You Tube/Facebook Channel Name :- CHEMISTRY BY DR A K SINGH

Chemistry by Dr A. K. Singh
Teaching Experience of 18+ years produces hundreds of Doctor and Engineer.

Structure of the Atom: Discovery of Sub-Atomic Particles
The structure of the atom has evolved over time as scientists conducted experiments and developed new theories to understand the nature of matter. The discovery of sub-atomic particles—protons, neutrons, and electrons—has been crucial in shaping our current understanding of atomic structure.

Here’s an overview of the major discoveries leading to the identification of sub-atomic particles:

1. Early Theories of the Atom
Before the discovery of sub-atomic particles, ancient philosophers like Democritus (around 400 BCE) proposed that matter was made up of indivisible particles called "atoms." However, this was purely a philosophical idea without experimental evidence.

It wasn’t until the 19th century that scientists began to investigate the atomic structure scientifically.

2. Discovery of the Electron (1897) – J.J. Thomson
The discovery of the electron was the first major breakthrough in understanding atomic structure. In 1897, British physicist J.J. Thomson conducted experiments using cathode rays (streams of electrons) and concluded that atoms are not indivisible, as previously thought, but contain smaller particles—electrons.

Experiment: Thomson passed an electric current through a cathode-ray tube and observed the deflection of the rays by electric and magnetic fields, which showed that they were negatively charged particles.
Conclusion: Thomson’s work led to the "plum pudding model" of the atom, where electrons were thought to be embedded in a positively charged "soup" or cloud, much like raisins in a pudding.
3. Discovery of the Nucleus (1911) – Ernest Rutherford
The next significant breakthrough came in 1911 with the work of Ernest Rutherford, who conducted the famous gold foil experiment.

Experiment: Rutherford and his colleagues bombarded a thin sheet of gold with alpha particles (positively charged helium nuclei). Most of the particles passed through the foil, but some were deflected at large angles, and a few even bounced back.
Conclusion: Rutherford concluded that the atom must have a small, dense, positively charged nucleus at its center, surrounded by mostly empty space. This led to the development of the nuclear model of the atom, where the atom is mostly empty space, and electrons orbit a dense nucleus.
4. Discovery of the Proton (1917) – Ernest Rutherford
In 1917, Rutherford discovered the proton, a positively charged particle in the nucleus, through his experiments with nitrogen and alpha particles.

Experiment: When Rutherford bombarded nitrogen gas with alpha particles, he observed the emission of hydrogen nuclei (protons).
Conclusion: Rutherford proposed that the hydrogen nucleus was a fundamental building block of all atomic nuclei and called it the "proton."
5. Discovery of the Neutron (1932) – James Chadwick
The final major discovery of sub-atomic particles came in 1932 with James Chadwick, who discovered the neutron.

Experiment: Chadwick bombarded beryllium with alpha particles, and the resulting radiation was found to be neutral and highly penetrating, suggesting the presence of a neutral particle with mass.
Conclusion: The neutral particle was named the neutron, and its discovery completed the basic structure of the atom—protons and neutrons in the nucleus, with electrons orbiting around it.
6. The Modern Atomic Model
With the discovery of protons, neutrons, and electrons, the modern atomic model evolved. Here’s a summary of the structure:

Nucleus: The dense, positively charged center of the atom, containing protons and neutrons. The protons determine the element (its atomic number), while neutrons contribute to the atom’s mass and stability.
Electrons: Negatively charged particles that orbit the nucleus in specific energy levels or shells. The arrangement of electrons determines the chemical properties and reactivity of the atom.
Key Summary of Sub-Atomic Particles:
Electron: Discovered by J.J. Thomson (1897), negatively charged, found outside the nucleus.
Proton: Discovered by Ernest Rutherford (1917), positively charged, found in the nucleus.
Neutron: Discovered by James Chadwick (1932), no charge (neutral), found in the nucleus.
Conclusion
The discovery of sub-atomic particles transformed our understanding of the atom, revealing that atoms are not indivisible, but composed of smaller particles. This laid the foundation for the development of modern atomic theory, quantum mechanics, and the exploration of the behavior of matter at atomic and sub-atomic levels.

#11th
#neet_2025
#Bihar bord
#Cbese Bord
#chemistry
#tranding
#viral
#viralvideo
#neet 2025
#motivationalvideo
#bihar
#patna
#educationmatters