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Atomic Structure — Syllabus

NIOS · Class 12 · Chemistry

What Atomic Structure covers in NIOS Class 12 Chemistry: 4 topics, for the 2026-27 session. Part of the NIOS Class 12 Chemistry syllabus.

45 questions30 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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4 Topics · NIOS Class 12 Chemistry · 2026-27

Topics in Atomic Structure

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1. Fundamental Particles of the Atom

  • Atoms are made up of three fundamental particles: Electron, Proton, and Neutron.
  • J.J. Thomson discovered the electron in 1897. He found it to be negatively charged with very little mass.
  • Proton is a positively charged particle found in the nucleus. It is approximately 1840 times heavier than an electron.
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2. Atomic Number, Mass Number, Isotopes, and Isobars

  • Atomic Number (Z) = Number of protons in the nucleus. In a neutral atom, Z also equals the number of electrons.
  • Mass Number (A) = Number of protons + Number of neutrons. A = Z + Number of neutrons.
  • Number of neutrons = A − Z.
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3. Earlier Models of the Atom

  • Thomson's Plum Pudding Model (1897): The atom is a large positively charged sphere with electrons embedded in it like plums in a pudding (also called Watermelon Model).
  • This model failed to explain Rutherford's gold foil experiment results.
  • Rutherford's Gold Foil (α-ray scattering) Experiment: A beam of fast-moving α-particles (positively charged helium ions, He²⁺) was fired at a very thin gold foil.
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4. Electromagnetic Radiation and Photon Energy

  • Electromagnetic (EM) radiation is a form of energy transmitted through space as oscillating electric and magnetic fields perpendicular to each other and to the direction of propagation.
  • EM radiations do NOT require any medium to travel — they can travel through vacuum.
  • All EM radiations travel at the speed of light: c = 3.0 × 10⁸ m s⁻¹.

Key Concepts

All atoms consist of three fundamentalAtomic number (Z) is the numberIsotopes are atoms of the sameJErnest Rutherford bombarded thin gold foil

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Frequently Asked Questions

What are the important topics in Atomic Structure for NIOS Class 12 Chemistry?
Key topics in Atomic Structure include Fundamental Particles of the Atom, Atomic Number, Mass Number, Isotopes, and Isobars, Earlier Models of the Atom, Electromagnetic Radiation and Photon Energy. Study these first, then practise questions on each for the NIOS Class 12 board exam.
How should I revise Atomic Structure for the NIOS Class 12 board exam?
Learn the core ideas first, then work through the 45 practice questions on Atomic Structure. Revise 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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