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Structure of the Atom

Gujarat Board · Class 9 · Science

Quick revision notes for Structure of the Atom — Gujarat Board Class 9 Science. Key concepts, formulas, and definitions for last-minute revision.

45 questions25 flashcards5 concepts

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An illustration of J.J. Thomson's atomic model, depicting an atom as a sphere of uniformly distributed positive charge with electrons (plums) embedded within it.
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Key Topics to Revise

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1. Charged Particles in Matter – Sub-Atomic Particles

  • Atoms are divisible and contain smaller particles called sub-atomic particles.
  • The three main sub-atomic particles are: Electron (e⁻), Proton (p⁺), and Neutron (n⁰).
  • J.J. Thomson discovered the electron.
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2. Atomic Models – Thomson, Rutherford, and Bohr

  • Thomson's Model (Plum Pudding / Watermelon Model): Atom is a positively charged sphere with electrons embedded in it like seeds in a watermelon or dry fruits in a Christmas pudding.
  • Thomson's model explained electrical neutrality but could NOT explain Rutherford's scattering results.
  • Rutherford's Alpha-Particle Scattering Experiment: Fast-moving alpha (α) particles were fired at a thin gold foil (1000 atoms thick).
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3. Distribution of Electrons in Shells (Bohr-Bury Rules)

  • The distribution of electrons in shells follows the Bohr-Bury scheme.
  • Rule 1: Maximum electrons in a shell = 2n², where n = shell number (1, 2, 3, 4...).
  • K shell (n=1): max 2 electrons. L shell (n=2): max 8 electrons. M shell (n=3): max 18 electrons. N shell (n=4): max 32 electrons.
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4. Valency

  • Valency is the combining capacity of an atom — how many bonds it can form.
  • Valency is determined by the number of electrons in the outermost shell (valence electrons).
  • If valence electrons ≤ 4: Valency = number of valence electrons (electrons lost or shared).

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Key Concepts

Atoms consist of three fundamental particlesJErnest Rutherford conducted the famous alphaNiels Bohr improved Rutherford's model byJ

Frequently Asked Questions

What are the important topics in Structure of the Atom for Gujarat Board Class 9 Science?
Key topics in Structure of the Atom include Flowchart showing the historical discovery of charged particles in atoms through electrical experiments, Pie chart showing the massive difference in mass between electrons and protons, Flowchart explaining Thomson's model and its basic features. These are the concepts Gujarat Board Class 9 examiners draw on most — study them first, then practise related questions.
How to score full marks in Structure of the Atom — Gujarat Board Class 9 Science?
Understand the core concepts first, then work through the 45 practice questions available for this chapter. Revise formulas and definitions regularly, and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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