Limitations of the Bohr Model
Where the planetary model fails and quantum mechanics begins
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Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. Why couldn't electrons circle the nucleus like planets, according to classical physics?
2. Which was a limitation of the Bohr model?
3. The Heisenberg uncertainty principle states that for a subatomic particle you cannot know precisely, at the same time, its…
4. In the present cloud model, electrons are described as…
5. A student thinks better instruments could measure an electron's exact position and momentum at once. Why not?
When the Bohr Model Breaks Down
The Bohr model predicts the spectral lines of hydrogen very accurately. However, when scientists applied it to helium and heavier atoms, its predictions did not match the measured spectra. Today, the electron cloud (quantum mechanical) model is used.
What is the main limitation of the Bohr model?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
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C1. How does the electron cloud model describe an electron’s location?
C2. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response using a mathematical relationship. (For atoms or ions with only one electron, the Bohr model gives En = −(13.6 eV)Z2n2, where Z is the number of protons.)
C3. For atoms or ions with only one electron, the Bohr model gives En = −(13.6 eV)Z2n2, where Z is the number of protons. Substitute numerical values into this mathematical representation to determine the ground-state (n = 1) energy of a Li2+ ion (lithium, Z = 3, with only one electron). Then calculate the energy.
C4. Place a check mark in three boxes to indicate the atoms or ions whose spectra the Bohr model predicts accurately.
C5. Which discovery helped lead to the electron cloud model?
C6. Identify one strength and one limitation of the Bohr model, and describe how the electron cloud model addresses the limitation.