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Chapter Analysis
Intermediate10 pages • EnglishQuick Summary
The chapter explores the structure of the atom, discussing the existence and arrangement of sub-atomic particles such as protons, neutrons, and electrons. It addresses various atomic models proposed by scientists like J.J. Thomson, Rutherford, and Bohr, and evaluates their effectiveness in explaining atomic structure. The chapter also explains concepts like atomic number, mass number, isotopes, and isobars. Furthermore, it introduces the periodic arrangement of electrons into shells and the concept of valency.
Key Topics
- •Structure of atom
- •Sub-atomic particles
- •Atomic models
- •Atomic number and mass number
- •Isotopes and isobars
- •Electron distribution
- •Valency
Learning Objectives
- ✓Understand the historical development of the atomic model
- ✓Explain the discovery and characteristics of sub-atomic particles
- ✓Describe the various atomic models and their limitations
- ✓Define and differentiate between isotopes and isobars
- ✓Illustrate the arrangement of electrons in various shells
- ✓Calculate the valency of elements
Questions in Chapter
Compare the properties of electrons, protons and neutrons.
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What are the limitations of J.J. Thomson’s model of the atom?
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What are the limitations of Rutherford’s model of the atom?
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Describe Bohr’s model of the atom.
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Summarise the rules for writing of distribution of electrons in various shells for the first eighteen elements.
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Define valency by taking examples of silicon and oxygen.
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Explain with examples (i) Atomic number, (ii) Mass number, (iii) Isotopes and iv) Isobars. Give any two uses of isotopes.
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Na+ has completely filled K and L shells. Explain.
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Additional Practice Questions
What is the significance of the discovery of the electron?
mediumAnswer: The discovery of the electron was significant because it provided the first evidence that atoms are not indivisible, as previously thought, but are composed of smaller sub-atomic particles. This discovery paved the way for further research into the structure of the atom and led to the development of new models to explain atomic behavior.
Discuss the experimental setup and conclusions of Rutherford’s gold foil experiment.
hardAnswer: In Rutherford’s gold foil experiment, alpha particles were directed at a thin sheet of gold foil. Most alpha particles passed straight through, indicating that most of the atom is empty space. A few were deflected at various angles, and a very small number bounced back, suggesting a dense, positively charged nucleus in the center of the atom.
How did Bohr’s model improve upon Rutherford’s model?
mediumAnswer: Bohr’s model of the atom introduced the concept of fixed, quantized orbits, or energy levels, within which electrons revolve around the nucleus without radiating energy. This addressed the instability issue in Rutherford’s model and explained atomic spectra more accurately.
Explain the concept of isotopes with examples.
easyAnswer: Isotopes are atoms of the same element that have the same atomic number but different mass numbers due to differing numbers of neutrons. For example, Carbon-12 and Carbon-14 are isotopes of carbon with mass numbers 12 and 14, respectively.
What are the uses of isotopes in various fields?
mediumAnswer: Isotopes have several applications; for instance, an isotope of uranium is used as a fuel in nuclear reactors, while an isotope of iodine is used in medical imaging and treatment of thyroid disorders.
NCERT Exemplar
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