What is the name of the model of the atom that describes electrons as orbiting the nucleus in specific energy levels?

Analysis

The question asks for the specific atomic model that introduced the concept of electrons occupying fixed, quantized energy levels (or shells) while orbiting the nucleus.

Concept Explanation

To understand this, let's look at the evolution of the atomic model:

1. Thomson Model ("Plum Pudding"): Proposed that the atom is a sphere of positive charge with electrons embedded in it like plums in a pudding. It did not feature a nucleus.
2. Rutherford Model ("Planetary Model"): Proposed that the atom has a small, dense, positively charged nucleus with electrons orbiting it like planets around the sun. However, it failed to explain why electrons didn't lose energy and spiral into the nucleus.
3. Bohr Model: Niels Bohr refined Rutherford's model by proposing that electrons can only exist in specific, stable energy levels (orbits) without radiating energy. Electrons can only move between these levels by absorbing or emitting specific amounts of energy (quanta).
4. Dalton Model: The earliest model, which viewed the atom as a solid, indivisible sphere.

Step-by-Step Solution

• Step 1: Evaluate the options based on the "energy levels" requirement.
• Step 2: Recognize that while Rutherford introduced the nucleus, he did not define the quantized energy levels.
• Step 3: Identify that the Bohr model specifically addresses the stability of the atom by restricting electrons to fixed orbits with defined energy values.
• Step 4: Conclude that the Bohr model is the correct description for electrons in specific energy levels.

Conclusion

The Bohr model is the correct answer as it successfully introduced the concept of stationary states (energy levels) to explain atomic stability and spectral lines.

Exam Tip: Remember the mnemonic "Bohr = Levels". Whenever you see a question about "energy levels," "shells," or "quantized orbits," the answer is almost always the Bohr model.