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Atomic Structure

NIOS · Class 12 · Chemistry

Quick revision notes for Atomic Structure — NIOS Class 12 Chemistry. Key concepts, formulas, and definitions for last-minute revision.

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Key Topics to Revise

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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.

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Full Notes

Key Concepts

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

Frequently Asked Questions

What are the important topics in Atomic Structure for NIOS Class 12 Chemistry?
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How to score full marks in Atomic Structure — NIOS Class 12 Chemistry?
Start by understanding all key concepts. Practise previous year questions from this chapter. Revise formulas and definitions regularly. Use flashcards for quick revision 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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