Question

For which of the following species Bohr’s theory is not applicable?

• A. \(Be^{3+}\)
• B. \(Li^{2+}\)
• C. \(He^{2+}\)
• D. \(H\)

Hint:

Bohr model works only for single-electron systems.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Bohr's model is valid only for single-electron systems. These include the hydrogen atom and hydrogen-like ions (ions that have been stripped of all but one electron).
Step 2: Detailed Explanation:
Let's check the number of electrons in each species:
- (A) \( \text{Be}^{3+} \): Atomic number \( Z=4 \). Neutral Be has 4 electrons. \( \text{Be}^{3+} \) has \( 4 - 3 = 1 \) electron. (Applicable).
- (B) \( \text{Li}^{2+} \): Atomic number \( Z=3 \). Neutral Li has 3 electrons. \( \text{Li}^{2+} \) has \( 3 - 2 = 1 \) electron. (Applicable).
- (C) \( \text{He}^{2+} \): Atomic number \( Z=2 \). Neutral He has 2 electrons. \( \text{He}^{2+} \) has \( 2 - 2 = 0 \) electrons. It is just a naked nucleus (alpha particle). Without an electron, the Bohr transitions cannot occur. (Not applicable).
- (D) \( \text{H} \): Atomic number \( Z=1 \). Neutral H has 1 electron. (Applicable).
Step 3: Final Answer:
Bohr's theory is not applicable to \( \text{He}^{2+} \).