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Bohr's postulates
Intermediate
Quantised angular momentum and photon emission by transitions.
L = nħ(1) Electrons stay in stationary orbits without radiating, (2) angular momentum L = nħ, (3) transitions emit or absorb photons with E = hf.
n = 1 is the ground state.
The model treats orbits as classical paths, which quantum mechanics later refined.
In more detail
Bohr's postulates say electrons occupy orbits where angular momentum is an integer multiple of h/2π, and that light is emitted when electrons jump between orbits, with energy equal to the difference.
Real-world uses
- The postulates predict the wavelengths of hydrogen spectral lines.
- They introduced quantisation into atomic physics.
- Students use Bohr's postulates to calculate the wavelengths of light emitted when hydrogen atoms drop between levels.
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Frequently asked questions
Why must angular momentum be quantised?
To match the observed discrete spectral lines and stable atomic states.
What is a photon's energy in a jump?
The difference in energy between the two orbits.
Why must angular momentum be quantised?
Bohr required it to match observed spectra, which is consistent with the later quantum mechanical picture.
Related topics in Atomic & Nuclear Physics
Rutherford's scattering experiment · Rutherford model limits · Bohr model · Radius of Bohr orbit · Energy of hydrogen levels · Hydrogen spectrum