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Cheat sheet · Class 12 · CBSE · Science Physics

Atoms cheat sheet

The whole chapter on one page: key formulas, facts and the points to remember, for quick revision before a test.

CBSE Class 12 · Physics

Cheat sheet

Chapter 12Atoms

Bohr: angular momentum quantised, L = nh/2π.

1. Rutherford Model

  • α-scattering: most pass, a few deflect, very few bounce back.
  • Nucleus tiny and dense.
  • Distance of closest approach: KE = kZe·2e/r₀.

2. Bohr Model (hydrogen)

mvr=nh2πmvr = \dfrac{nh}{2\pi}rn=0.53n2r_n = 0.53n^2 Å
En=−13.6n2E_n = -\dfrac{13.6}{n^2} eVhν=Ei−Efh\nu = E_i - E_f
1λ=R(1n12−1n22)\dfrac1\lambda = R\left(\dfrac1{n_1^2} - \dfrac1{n_2^2}\right)

3. Spectral Series

Seriesn₁Region
Lyman1UV
Balmer2visible
Paschen3IR
Brackett4IR
Pfund5IR

4. Key Points

  • Ionisation energy of H = 13.6 eV.
  • Bohr model fails for many-electron atoms.
  • Line spectra are atomic fingerprints.
  • Excitation needs exact energy.

Remember: Rutherford | Bohr r, E | 5 series

Atoms: questions and notes

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