Question

Which of the following statement is NOT true with Bohr's model of atom?

• A. It accounts the stability and line spectra of \( \text{He}^+ \)
• B. It fails to account for the finer details of the hydrogen atom spectrum by using sophisticated spectroscopic techniques.
• C. It is unable to explain the spectrum of atom/ion which possess only two electrons.
• D. It only explains about the splitting of spectral lines in the presence of electric field.
• E. It is unable to explain the ability of atoms to form molecules by chemical bonds.

Hint:

Bohr’s model works well only for one-electron species. It cannot explain fine structure, Stark effect, Zeeman effect, multi-electron atoms, or chemical bonding.

Answer 1

The Correct Option is D

Step 1: Recall the success of Bohr’s model.
Bohr’s atomic model successfully explains: \[ \text{(i) stability of hydrogen-like atoms} \] and \[ \text{(ii) line spectrum of one-electron systems such as H, He}^+, \text{Li}^{2+} \] So statement (1) is true for \( \text{He}^+ \), because it is a hydrogen-like ion with only one electron.

Step 2: Recall the limitations of Bohr’s model.
Bohr’s model fails to explain: \[ \text{fine structure of spectral lines} \] \[ \text{Zeeman effect (magnetic field splitting)} \] \[ \text{Stark effect (electric field splitting)} \] \[ \text{multi-electron atoms} \] \[ \text{chemical bonding} \] So statements that describe these failures are true limitations of the model.

Step 3: Check statement (2).
Statement (2) says Bohr’s model fails to explain the finer details of hydrogen spectrum.
This is correct. The model cannot explain fine structure observed in high-resolution spectroscopy.

Step 4: Check statement (3).
Statement (3) says it cannot explain atoms or ions with more than one electron.
This is also correct, because Bohr’s model works only for one-electron systems and not for two-electron or many-electron species.

Step 5: Check statement (5).
Statement (5) says Bohr’s model cannot explain chemical bonding and molecule formation.
This is again true. Bohr’s model is too simple to account for molecular bonding.

Step 6: Check statement (4) carefully.
Statement (4) says: \[ \text{It only explains about the splitting of spectral lines in the presence of electric field.} \] This is NOT true, because Bohr’s model does not explain splitting of spectral lines in electric field at all.
That phenomenon is the Stark effect, which Bohr’s model fails to account for.

Step 7: Final conclusion.
Hence, the statement which is NOT true is \[ \boxed{\text{It only explains about the splitting of spectral lines in the presence of electric field.}} \] Therefore, the correct option is \[ \boxed{(4)} \]