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Atom, Origin of Spectra: Bohr's Theory of Hydrogen Atom

ICSE · Class 12 · Physics

Quick revision notes for Atom, Origin of Spectra: Bohr's Theory of Hydrogen Atom — ICSE Class 12 Physics. Key concepts, formulas, and definitions for last-minute revision.

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Key Topics to Revise

1

Alpha-Particle Scattering and Rutherford's Nuclear Model

  • Most alpha particles passed straight through a thin gold foil, so most of the atom is empty space.
  • A small number of alpha particles were deflected through large angles, which showed that the positive charge and most of the mass are concentrated in a very small central region.
  • The central region is called the nucleus.
2

Bohr's Atomic Model and Postulates

  • Bohr removed the difficulties of Rutherford's model by applying Planck's quantum theory.
  • Electrons revolve around the nucleus only in certain circular orbits called stationary orbits.
  • In a stationary orbit, the electron does not radiate energy even though it is accelerated.
3

Radii, Speed and Energy of Bohr Orbits

  • The radii of permitted orbits are proportional to n^2.
  • For hydrogen-like atoms, the radius decreases when atomic number Z increases.
  • The first Bohr radius of hydrogen is 0.53 Å.
4

Discrete Energy Levels, Excitation and Ionisation

  • Atoms absorb and emit energy only in definite amounts, so their energy states are discrete.
  • Mercury vapour shows discrete absorbed energies of 4.86 eV, 6.67 eV, ... and 10.4 eV.
  • The ionised state is the highest listed state in the mercury energy-level scheme.

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Key Concepts

HighRutherford proposed that the atom hasThe atomic number Z isBohr said that electrons revolve onlyFor hydrogen

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Atom, Origin of Spectra: Bohr's Theory of Hydrogen Atom covers several key topics that are frequently asked in ICSE Class 12 board exams. Focus on the core concepts listed on this page and practise related questions to build confidence.
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Understand the core concepts first, then work through the 59 practice questions available for this chapter. Revise formulas and definitions regularly, and use flashcards for quick recall before the exam.

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