Which of the following is a feature of the Bohr model but not of the quantum mechanical model?

• A. Electrons travel in fixed, circular orbits around the nucleus.
• B. Electrons can exist between energy levels.
• C. Energy levels are quantized.
• D. Electron positions are described by probability distributions (orbitals).

Answer: (A)

Verified step by step guidance

1. Understand that the Bohr model and the quantum mechanical model are both used to describe electrons in atoms, but they differ fundamentally in how they depict electron behavior.
2. Recall that the Bohr model describes electrons as moving in fixed, circular orbits around the nucleus, with specific allowed energy levels. This means electrons have precise paths and distances from the nucleus.
3. Recognize that the quantum mechanical model replaces these fixed orbits with orbitals, which are regions of space where there is a high probability of finding an electron, rather than exact paths.
4. Note that in the quantum mechanical model, electrons do not travel in fixed orbits but are described by wavefunctions that give probability distributions, allowing electrons to exist in regions between classical energy levels.
5. Conclude that the feature unique to the Bohr model is the concept of electrons traveling in fixed, circular orbits around the nucleus, which is not present in the quantum mechanical model.