Answer: Atoms and molecules are the fundamental building blocks of matter.
2. Question: Why do different kinds of matter exist?
Answer: Different kinds of matter exist because they are made up of different atoms.
3. Question: What question did Dalton’s atomic theory raise?
Answer: It raised the question of whether atoms are really indivisible or contain smaller particles.
4. Question: What are sub-atomic particles?
Answer: Sub-atomic particles are smaller particles present inside an atom, such as electrons, protons, and neutrons.
5. Question: Which experiment showed that atoms are divisible?
Answer: Experiments related to electricity and charged particles showed that atoms are divisible.
6. Question: What happens when two objects are rubbed together?
Answer: They become electrically charged.
7. Question: From where does electric charge come?
Answer: Electric charge comes from charged particles present inside atoms.
8. Question: Name the first sub-atomic particle discovered.
Answer: Electron.
9. Question: Who discovered the electron?
Answer: J. J. Thomson discovered the electron.
10. Question: What are canal rays?
Answer: Canal rays are positively charged radiations discovered in gas discharge experiments.
11. Question: Who discovered canal rays?
Answer: E. Goldstein discovered canal rays in 1886.
12. Question: Which particle was discovered due to canal rays?
Answer: Proton.
13. Question: What is the charge of a proton?
Answer: Positive charge (+1).
14. Question: What is the charge of an electron?
Answer: Negative charge (–1).
15. Question: Compare the mass of a proton and an electron.
Answer: A proton is about 2000 times heavier than an electron.
16. Question: How is an electron represented?
Answer: An electron is represented by ‘e⁻’.
17. Question: How is a proton represented?
Answer: A proton is represented by ‘p⁺’.
18. Question: What did J. J. Thomson propose about the structure of an atom?
Answer: He proposed that an atom contains electrons embedded in a positively charged sphere.
19. Question: Which model of atom was proposed by J. J. Thomson?
Answer: Plum pudding model (or watermelon model).
20. Question: Why is Thomson’s model called the plum pudding model?
Answer: Because electrons were thought to be embedded like plums in a positively charged sphere.
21. Question: What is the limitation of Thomson’s model?
Answer: It could not explain the results of Rutherford’s gold foil experiment.
22. Question: Which experiment led to the discovery of the nucleus?
Answer: Rutherford’s alpha-particle scattering experiment.
23. Question: What was the gold foil used in Rutherford’s experiment?
Answer: A thin sheet of gold.
24. Question: What were alpha particles?
Answer: Alpha particles are positively charged particles used in scattering experiments.
25. Question: What observation showed that most of the atom is empty?
Answer: Most alpha particles passed straight through the gold foil without deflection.
26. Question: What did the large deflection of alpha particles indicate?
Answer: It indicated the presence of a small, dense, positively charged nucleus.
27. Question: Where is most of the mass of an atom concentrated?
Answer: In the nucleus.
28. Question: Where are electrons located according to Rutherford?
Answer: Electrons revolve around the nucleus in circular paths.
29. Question: What is valency?
Answer: Valency is the combining capacity of an atom, determined by the number of electrons in the outermost shell.
30. Question: What are valence electrons?
Answer: Electrons present in the outermost shell of an atom are called valence electrons.
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