QCM : Atomic Structure and Spectra — 8 questions

Questions et réponses du QCM

1. How is Bohr's quantization condition applied to determine the properties of an electron's orbit in practice?

By calculating the radius of the orbit using the relation $ r = rac{n bar}{m v} $
By setting the angular momentum equal to an integer multiple of $bar$, i.e., $ m v r = n bar $, to find allowed orbits
By assuming the electron's velocity is constant and equal to $ v = rac{bar}{m r} $
By deriving the energy levels directly from the classical Coulomb force without considering angular momentum

By setting the angular momentum equal to an integer multiple of $bar$, i.e., $ m v r = n bar $, to find allowed orbits

Explication

Bohr's quantization condition states that the angular momentum $ m v r $ is quantized as $ n bar $. To determine the properties of an electron's orbit, this relation is used as a fundamental restriction, allowing calculation of the allowed orbits' radii and energies. The correct application involves setting $ m v r = n bar $ as a constraint for allowed orbits, which is explicitly supported by the source.

2. What is the key property that defines allowed stationary orbits in Bohr's model of the atom?

Electrons in these orbits are only theoretical and do not exist in reality
Electrons in these orbits can have any radius and velocity, as long as they are circular
Electrons in these orbits do not emit radiation and are stabilized by quantized angular momentum
Electrons in these orbits have random energies and radiate energy continuously

Electrons in these orbits do not emit radiation and are stabilized by quantized angular momentum

Explication

Allowed stationary orbits are characterized by the fact that electrons in these orbits do not radiate energy and are stabilized by the quantization of angular momentum. This property makes these orbits stable and discrete, unlike arbitrary paths or non-physical states.

3. What does energy absorption and emission fundamentally mean in atomic transitions?

Atoms absorb energy from external fields but do not emit energy.
Electrons emit light spontaneously without energy change.
Electrons gain or lose energy by absorbing or emitting photons when moving between energy levels.
Energy levels in atoms are continuous, allowing electrons to gain any amount of energy.

Electrons gain or lose energy by absorbing or emitting photons when moving between energy levels.

Explication

Energy absorption and emission involve electrons taking in or releasing energy in the form of photons during transitions between quantized energy levels. This process explains spectral lines and is fundamental to atomic spectra. The other options are incorrect because they either describe incomplete or inaccurate processes or contradict the concept of quantized energy levels.

4. Who formulated the hydrogen atom model that introduced quantized angular momentum and stationary orbits?

Dalton
Schrödinger
Rutherford
Bohr

Bohr

Explication

The source states that Bohr formulated the hydrogen atom model in 1913, introducing the concept of quantized angular momentum and stationary orbits, which is the basis of his atomic model.

5. In what year did Bohr publish his work on atomic structure?

1913
1905
1920
1918

1913

Explication

Bohr published his groundbreaking work on atomic structure in 1913, introducing the quantization of angular momentum. The other years are incorrect and serve as distractors to test students' knowledge of the historical timeline of atomic theory development.

6. What is the cause of the changes in the size, energy, and velocity of electrons in hydrogen-like atoms as the atomic number Z varies?

External magnetic fields cause the electron velocity to decrease and the orbit radius to increase.
Temperature changes cause the energy levels to shift, affecting the electron velocity and orbit radius.
Increase in nuclear charge Z causes the orbit radius to decrease, the energy levels to become more negative, and the electron velocity to increase.
Electron-electron repulsion causes the orbit radius to increase and the energy levels to become less negative.

Increase in nuclear charge Z causes the orbit radius to decrease, the energy levels to become more negative, and the electron velocity to increase.

Explication

An increase in nuclear charge Z causes a stronger electrostatic attraction between the nucleus and the electron, which results in a smaller orbit radius, more negative energy levels, and higher electron velocity, as explained in the source content.

7. When was Bohr's theory that explains excitation and ionization energies established?

1927
1913
1897
1945

1913

Explication

Bohr's theory was established in 1913, introducing quantized angular momentum and the concept of stationary orbits, which underpin the understanding of excitation and ionization energies.

8. How does Bohr's theory's limitation in explaining fine spectral structure differ from its limitation to hydrogen-like atoms?

It can explain fine structure in multi-electron atoms but not in hydrogen.
It cannot account for small spectral line splittings, unlike its restriction to simple atoms.
It fails to predict spectral lines in hydrogen but can model multi-electron atoms accurately.
Its inability to explain fine structure is unrelated to its applicability only to hydrogen-like atoms.

Its inability to explain fine structure is unrelated to its applicability only to hydrogen-like atoms.

Explication

Bohr's theory cannot explain the detailed splitting of spectral lines (fine structure) and is mainly applicable to hydrogen and hydrogen-like atoms. The limitation regarding fine spectral structure is a specific phenomenon that arises from quantum effects not included in Bohr's classical model, and it is separate from the broader scope limitation that it only works well for single-electron systems.

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Mémorisez les réponses avec 16 flashcards sur Atomic Structure and Spectra.

Bohr's quantization condition

Electron angular momentum is quantized as discrete values.

Allowed stationary orbits

Electrons in stable, non-radiating orbits with quantized radii and velocities.

Energy absorption — process?

Electron absorbs photon energy to move to a higher energy level.

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