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Bohr’s Model for Hydrogen Atom

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Estimated time: 11 minutes
CBSE: Class 12

Formula: Orbital Speed of Electron

\[v=\frac{2\pi kZe^2}{nh}\]

For hydrogen atom (Z = 1):

\[v=\frac{2\pi ke^2}{nh}=\alpha\frac{c}{n}\]

where α is the fine structure constant and \[\alpha=\frac{1}{137}.\]

CBSE: Class 12

Formula: Radius of Orbit

\[r=\frac{n^2h^2}{4\pi^2mkZe^2}\]

CBSE: Class 12

Formula: Radius of Bohr Orbit

Radius of the n-th Bohr Orbit (General):

\[r_n=\frac{\varepsilon_0n^2h^2}{\pi mZe^2}\]

\[\mathrm{i.e.,}r_n\propto n^2\mathrm{and}r_n\propto\frac{1}{Z}\]

Radius of n-th orbit for Hydrogen-like atom:

\[r_n=0.53\left(\frac{n^2}{Z}\right)\mathrm{\r{A}}\]

CBSE: Class 12

Formula: Velocity of Electron in n-th Orbit

\[v_n=\frac{nh}{2\pi mr_n}\]

CBSE: Class 12

Formula: Total Energy of Electron in nth Orbit

Total Energy of Electron in n-th Orbit (General):

  • \[E_n=\frac{-Z^2me^4}{8\varepsilon_0^2n^2h^2}\]

Total Energy (Alternate form):

  • \[E_n=-\frac{2\pi^2mk^2Z^2e^4}{n^2h^2}\]

Total Energy for Hydrogen-like Atom (Simplified):

  • \[E_n=-13.6\frac{Z^2}{n^2}\mathrm{eV},\quad n=1,2,3\ldots\]
CBSE: Class 12
Maharashtra State Board: Class 12

Key Points: Bohr's Model for Hydrogen Atom

  • The radius of Bohr's orbit is proportional to \[n^{2}\] and inversely proportional to Z.
  • For hydrogen (Z = 1), the ground state (n = 1) radius is 0.53 Å, known as Bohr's radius.
  • The velocity of an electron decreases as the orbital number (n) increases.
  • For hydrogen, orbital speed of electron equals \[\alpha\frac{c}{n}\]​, where \[\alpha=\frac{1}{137}\]​.
  • The total energy of an electron in any orbit is negative, indicating a bound state.
  • For hydrogen-like atoms, the energy of an electron in the n-th orbit is \[-13.6\frac{Z^2}{n^2}\mathrm{~eV}.\] .

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Shaalaa.com | Atoms part 8 (Bohr model and atomic spectra)

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Atoms part 8 (Bohr model and atomic spectra) [00:15:10]
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