Neils Bohr and His Model of the Atom – Long Answer Questions

Medium Level (Application & Explanation)

Q1. Explain how Bohr solved the problem of instability in Rutherford’s model.

Answer:

Rutherford’s model had electrons revolving like planets.
Moving charges should lose energy and fall into the nucleus.
Bohr said electrons move only in discrete orbits or fixed energy levels.
In these orbits, electrons do not radiate energy. They stay stable.
Energy is lost or gained only when electrons jump between levels.
This explains why atoms do not collapse and remain stable.

Q2. Describe Bohr’s idea of energy levels using K, L, M, N (n = 1, 2, 3, 4). Give simple examples.

Answer:

Bohr labelled energy levels as K, L, M, N or n = 1, 2, 3, 4.
K (n=1) is closest to the nucleus and has the lowest energy.
L (n=2), M (n=3), N (n=4) are farther and have higher energy.
An electron in L has more energy than in K.
If an electron moves from L to K, it releases energy as light.
If it moves from K to L, it absorbs energy to jump up.

Q3. What are “discrete orbits” in Bohr’s model? Why do electrons not lose energy in these orbits?

Answer:

Discrete orbits are fixed paths with fixed energies for electrons.
Electrons in these orbits have stationary energy.
They do not emit radiation while revolving in these orbits.
They change energy only by absorbing or emitting a photon.
This rule prevents continuous energy loss.
So, atoms stay stable and do not collapse.

Q4. Define ground state and excited state. How does Bohr’s model explain spectral lines?

Answer:

The ground state is the lowest energy level, usually K (n=1).
An excited state is a higher energy level like L, M, N.
An electron absorbs energy and moves to an excited state.
It later returns to a lower level by emitting a photon.
Each jump releases a specific energy (specific color of light).
These appear as spectral lines in the atom’s spectrum.

Q5. Briefly explain Bohr’s contributions and why he is important in atomic theory.

Answer:

Neils Bohr was born on 7 October 1885 in Copenhagen.
He became a Professor at Copenhagen University in 1916.
He got the Nobel Prize in 1922 for atomic structure work.
He gave the idea of quantized energy levels and discrete orbits.
His model explained atomic stability and spectral lines.
His work inspired modern physics and future scientists.

High Complexity (Analysis & Scenario-Based)

Q6. A hydrogen atom absorbs energy that matches the gap from L (n=2) to M (n=3). Predict what happens and what you observe.

Answer:

The electron in n=2 will absorb a photon of exact required energy.
It will jump to n=3, so the atom becomes excited.
While excited, it is less stable and soon returns to a lower level.
On returning, it emits photons with specific energies.
You observe spectral lines at fixed wavelengths.
These lines prove quantized energy levels in Bohr’s model.

Q7. If electrons could move in any orbit (not discrete), how would atomic stability and spectra change?

Answer:

Electrons would radiate continuously while moving.
They would lose energy and spiral into the nucleus.
Atoms would become unstable and matter would not last.
Spectra would be continuous, not line spectra.
No fixed colors would appear for an element.
This contradicts real observations, so Bohr’s discrete orbits are needed.

Q8. An electron moves from L (n=2) to K (n=1). Analyze the energy change and what an observer detects.

Answer:

The electron is moving to a lower energy level.
It must release energy to complete this jump.
The released energy comes out as a photon of light.
The frequency or color depends on the energy gap.
An observer detects a bright line in the emission spectrum.
This supports Bohr’s idea of fixed energy differences.

Q9. Imagine Rutherford’s model was fully correct and electrons kept radiating in circular paths. What would be the real-world effects?

Answer:

Electrons would keep losing energy while moving.
They would fall into the nucleus very quickly.
Atoms would not be stable for long.
Matter as we know it would not exist in its stable form.
No fixed chemical properties would be seen in elements.
This is not true in reality, so Bohr’s stability postulate is essential.

Q10. You change the metal foil in a scattering experiment. Connect this to Bohr’s model and predict observations.

Answer:

Different metals have different atomic numbers and nuclei.
Scattering angles change with nuclear charge and density.
Heavier nuclei cause greater deflection of alpha particles.
Rutherford’s experiment shows a small, dense nucleus.
Bohr built on this and added discrete electron orbits around the nucleus.
You observe changed scattering, but atoms still show stable orbits as per Bohr.

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