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History of Atoms Video Lecture - Class 9

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1. What is the history of the discovery of atoms?
Ans. The history of the discovery of atoms dates back to ancient times. The concept of atoms was first proposed by the ancient Greek philosopher Democritus around 400 BC. However, it was not until the early 19th century that the scientific community started to gather concrete evidence for the existence of atoms through various experiments and observations.
2. Who discovered the electron and when?
Ans. The electron was discovered by J.J. Thomson in 1897. He conducted a series of experiments using cathode rays and concluded that they were composed of tiny, negatively charged particles, which he called electrons. This discovery laid the foundation for our understanding of atomic structure.
3. When was the atomic theory proposed and by whom?
Ans. The atomic theory was proposed by John Dalton in the early 19th century. In 1803, Dalton published his atomic theory, which stated that all matter is composed of indivisible particles called atoms. He also proposed that atoms of different elements have different properties and combine in simple whole number ratios to form compounds.
4. How did the discovery of the atomic nucleus contribute to our understanding of atoms?
Ans. The discovery of the atomic nucleus by Ernest Rutherford in 1911 revolutionized our understanding of atoms. Rutherford conducted the famous gold foil experiment, where he bombarded thin gold foil with alpha particles. He observed that some particles were deflected, suggesting the presence of a concentrated positive charge at the center of the atom, which he called the atomic nucleus. This discovery led to the development of the nuclear model of the atom.
5. What are the major contributions of Niels Bohr to the atomic theory?
Ans. Niels Bohr made significant contributions to the atomic theory by proposing the Bohr model of the atom in 1913. He suggested that electrons orbit the atomic nucleus in specific energy levels or shells, and they can only exist in these discrete energy states. This model explained the stability of atoms and the emission and absorption of light by atoms. Bohr's model also laid the foundation for the understanding of quantum mechanics and the wave-particle duality of electrons.
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