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Atom, Origin of Spectra: Bohr's Theory of Hydrogen Atom — Revision Notes

ICSE · Class 12 · Physics

Atom, Origin of Spectra: Bohr's Theory of Hydrogen Atom revision notes for ICSE Class 12 Physics: 4 topics in quick points.

59 questions35 flashcards7 formulas & key relations5 concepts

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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

Frequently Asked Questions

What are the important topics in Atom, Origin of Spectra: Bohr's Theory of Hydrogen Atom for ICSE Class 12 Physics?
Key topics in Atom, Origin of Spectra: Bohr's Theory of Hydrogen Atom include Alpha-Particle Scattering and Rutherford's Nuclear Model, Bohr's Atomic Model and Postulates, Radii, Speed and Energy of Bohr Orbits, Discrete Energy Levels, Excitation and Ionisation. Study these first, then practise questions on each for the ICSE Class 12 board exam.
How should I revise Atom, Origin of Spectra: Bohr's Theory of Hydrogen Atom for the ICSE Class 12 board exam?
Learn the core ideas first, then work through the 59 practice questions on Atom, Origin of Spectra: Bohr's Theory of Hydrogen Atom. Revise definitions regularly and use flashcards for quick recall before the exam.

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