Question

For which one of the following, Bohr model is not valid?

• A. Hydrogen atom
• B. Singly ionised helium atom $(He^+)$
• C. Deuteron atom
• D. Singly ionised neon atom $(Ne^+)$

Answer 1

The Correct Option is D

The Bohr model provides a simplistic view of an atom that accurately describes hydrogen-like atoms, i.e., systems with a single electron orbiting a nucleus. Let's evaluate the options based on this understanding:

1. Hydrogen atom: The Bohr model is explicitly designed for the hydrogen atom. It describes a single electron orbiting the nucleus, which matches the simple electron configuration required.
2. Singly ionised helium atom \((He^+)\): This ion, like a hydrogen atom, has only one electron. The Bohr model is applicable, as it describes single-electron systems.
3. Deuteron atom: A deuteron is a specific isotope of hydrogen (deuterium nucleus) and the Bohr model applies to deuterium in the same manner as the normal hydrogen atom, treating it as a single electron system.
4. Singly ionised neon atom \((Ne^+)\): Neon originally has 10 electrons, and even when singly ionized, it still has 9 remaining electrons. The Bohr model is not valid here because it cannot accurately describe multi-electron systems with electron-electron interactions and complex orbits.

Therefore, the correct answer is the Singly ionised neon atom \((Ne^+)\) because the Bohr model cannot account for the complexities of multi-electron atoms. The Bohr model's assumptions break down in such cases due to interactions between electrons, requiring more sophisticated quantum mechanical models.