SCIENCE - CLASS IX - STRUCTURE OF THE ATOM
Chapter-wise Multiple Choice Questions with Instant Feedback
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- Electron Discovery: J.J. Thomson (1897) through cathode ray experiment; charge: -1, mass: ~1/2000 u.
- Proton Discovery: E. Goldstein (1886) through canal rays; charge: +1, mass: 1 u.
- Neutron Discovery: James Chadwick (1932); charge: 0, mass: 1 u.
- Thomson's Model: Plum pudding model - positive sphere with embedded electrons.
- Rutherford's Model: Nuclear model - dense positive nucleus with orbiting electrons.
- Rutherford's Experiment: Gold foil experiment showing most alpha particles passed through (empty space), some deflected (positive nucleus), few rebounded (dense nucleus).
- Bohr's Model: Electrons in discrete orbits (K, L, M, N) without radiating energy.
- Shell Capacity: Maximum electrons = 2n² (K=2, L=8, M=18, N=32).
- Valence Electrons: Electrons in outermost shell determining chemical properties.
- Atomic Number (Z): Number of protons in nucleus (defines the element).
- Mass Number (A): Sum of protons and neutrons (A = Z + N).
- Isotopes: Same element (same Z), different mass numbers (different neutrons).
- Isobars: Different elements (different Z), same mass numbers.
- Valency: Combining capacity = electrons lost/gained/shared to complete octet.
- Electronic Configuration: Distribution of electrons in shells (e.g., Sodium: 2,8,1).
Basic Level Questions
Chapter Summary
Unlocking the Secrets of Matter's Building Blocks: Chapter 4, "Structure of the Atom," takes you on an incredible journey inside the atom, revealing the fascinating world of subatomic particles and the evolution of atomic models. This chapter bridges the gap between the macroscopic world we see and the microscopic realm that defines all matter. From Thomson's plum pudding to Rutherford's nuclear model and Bohr's revolutionary orbits, you'll discover how scientists progressively unraveled the atom's mysteries through ingenious experiments and brilliant deductions.
What You Will Learn from This Chapter & How This Website Helps: This chapter transforms abstract concepts into tangible understanding by exploring the discovery of electrons, protons, and neutrons, and the development of atomic models that explain their arrangement. You'll master crucial concepts like atomic number, mass number, isotopes, and isobars, and learn to write electronic configurations for any element. The chapter culminates in understanding valency - the key to chemical bonding. Our website reinforces this learning through carefully crafted MCQs that test your conceptual clarity and problem-solving skills. From identifying elements based on their electronic configuration to calculating the number of subatomic particles in isotopes, our questions ensure you're thoroughly prepared for board exams and competitive tests. The instant feedback and detailed explanations help you identify knowledge gaps and build the confidence needed to tackle any question on atomic structure.