Chapter 4 of 12
Syllabus
Structure of the Atom — Syllabus
Karnataka Board · Class 9 · Science
What Structure of the Atom covers in Karnataka Board Class 9 Science: 4 topics, for the 2026-27 session. Topics include Discovery of Sub-atomic Particles.
44 questions20 flashcards2 formulas & key relations5 concepts
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4 Topics · Karnataka Board Class 9 Science · 2026-27
Topics in Structure of the Atom
1
Discovery of Sub-atomic Particles
- Static electricity experiments showed that atoms contain charged particles
- J.J. Thomson discovered electrons (e⁻) - negatively charged particles with negligible mass
- E. Goldstein discovered canal rays (1886) which led to discovery of protons
2
Atomic Models
- Thomson's Model (Plum Pudding): Electrons embedded in a sphere of positive charge like seeds in watermelon
- Rutherford's α-particle scattering experiment used fast-moving α-particles on thin gold foil
- Observations: Most α-particles passed straight through, few deflected, very few bounced back 180°
3
Electronic Configuration and Shell Filling Rules
- Electrons fill shells in order: K, L, M, N (n = 1, 2, 3, 4)
- Maximum electrons: K=2, L=8, M=18, N=32
- Outermost shell can hold maximum 8 electrons (octet rule)
4
Valency
- Valency is the combining capacity of an atom
- Depends on number of electrons in outermost shell
- Atoms try to achieve stable octet (8 electrons) in outermost shell
Key Concepts
Atoms contain three main particlesThomson proposed the 'plum pudding' modelRutherford bombarded a thin gold foilBohr proposed that electrons revolve aroundElectrons are arranged in shells following
Work through every topic in Structure of the Atom with notes and quizzes
Start This ChapterFrequently Asked Questions
What are the important topics in Structure of the Atom for Karnataka Board Class 9 Science?
Key topics in Structure of the Atom include Discovery of Sub-atomic Particles, Atomic Models, Electronic Configuration and Shell Filling Rules, Valency. Study these first, then practise questions on each for Class 9 exams.
How should I revise Structure of the Atom for Class 9 exams?
Learn the core ideas first, then work through the 44 practice questions on Structure of the Atom. Revise definitions regularly and use flashcards for quick recall before the exam.
Sources & Official References
- Karnataka SSLC — kseeb.kar.nic.in
- Dept of Pre-University Education, Karnataka
- National Education Policy 2020 — education.gov.in
Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.
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