AP Physics 2 Quiz: The Bohr Model Of Atomic Structure

What this quiz covers

This quiz focuses on The Bohr Model Of Atomic Structure, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Physics 2.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. The electron moves from $n=2$ to $n=1$.
2. The electron moves from $n=5$ to $n=1$. (correct answer)
3. The electron moves from $n=3$ to $n=2$.
4. The electron moves from $n=4$ to an energy between $n=3$ and $n=4$.

Explanation: This question tests the Bohr model of atomic structure. In the Bohr model, the energy of emitted photons equals the difference between initial and final energy levels during downward transitions. The highest-energy photon comes from the largest energy difference, which occurs when an electron falls from the highest allowed level to the lowest allowed level. The transition from n=5 to n=1 represents the maximum possible energy difference among the given options, producing the highest-energy photon. Choice D incorrectly suggests the electron can transition to an energy between allowed levels, which violates the quantization principle. Remember: the largest energy gap between allowed levels produces the highest-energy photon.

Question 2

1. The electron spirals from $n=2$ into the nucleus.
2. The electron moves from $n=3$ to any energy between $n=2$ and $n=3$.
3. The electron moves from $n=2$ to $n=4$. (correct answer)
4. The electron moves from $n=4$ to $n=2$.

Explanation: This question tests the Bohr model of atomic structure. In the Bohr model, photon absorption occurs when an electron gains energy and moves from a lower allowed energy level to a higher allowed energy level. The transition from n=2 to n=4 requires the electron to absorb a photon with energy exactly equal to E₄ - E₂. This is the only option that represents an upward transition between allowed levels. Choice C incorrectly suggests the electron can move to an energy between allowed levels, which violates the quantization principle of the Bohr model. Remember: absorption requires upward transitions between allowed levels, while emission requires downward transitions.

Question 3

1. The electron moves from $n=2$ to $n=4$ only (correct answer)
2. The electron moves from $n=2$ to $n=1$ only
3. The electron spirals inward and emits continuously
4. The electron drifts to any radius between $n=2$ and $n=4$

Explanation: This question tests understanding of the Bohr model of atomic structure. In the Bohr model, electrons can only exist in specific quantized orbits, and photon absorption occurs when an electron gains energy to jump to a higher level. From n=2, absorption means the electron must move to a higher energy level like n=3 or n=4, not drop to n=1 (which would be emission). The electron gains exactly the energy difference between the two levels by absorbing a photon of that specific energy. Choice D incorrectly suggests the electron can drift to any radius, violating the fundamental principle of discrete orbits. Remember that absorption always involves transitions to higher n values.

Question 4

1. It is converted into orbital radius without photon emission
2. It is emitted as a single photon with energy elta E (correct answer)
3. It is radiated continuously as the electron spirals inward
4. It is lost because the electron can occupy forbidden energies

Explanation: This question tests understanding of the Bohr model of atomic structure. In the Bohr model, when an electron transitions between allowed energy levels, the energy difference is conserved by emission or absorption of a photon. When dropping from n=3 to n=1, the electron loses energy equal to the difference between these levels, and this energy is carried away by a single photon. The transition is instantaneous, with no intermediate states or continuous radiation. Choice B incorrectly suggests continuous radiation during spiraling, which contradicts the discrete nature of Bohr transitions. The fundamental principle is that energy differences between levels are always converted to photons with matching energy.

Question 5

1. No photon is involved because energies between $n=3$ and $n=2$ are continuous.
2. A photon is emitted because the electron moves to a lower allowed energy level. (correct answer)
3. A photon is absorbed because the electron moves to a lower allowed energy level.
4. The electron spirals into the nucleus while radiating continuously.

Explanation: This question tests understanding of the Bohr model of atomic structure. In the Bohr model, electrons can only occupy specific, quantized energy levels (n=1, 2, 3, etc.), and any energies between these levels are forbidden. When an electron transitions from a higher energy level (n=3) to a lower energy level (n=2), it must release energy equal to the difference between these levels. This energy is released as a photon, making the transition an emission process. Choice C incorrectly assumes continuous energies are allowed between levels, which violates the fundamental quantization principle of the Bohr model. Remember: transitions to lower energy levels always emit photons, while transitions to higher levels require photon absorption.

Question 6

1. The electron moves from $n=4$ to $n=1$. (correct answer)
2. The electron moves from $n=2$ to $n=1$.
3. The electron moves from $n=4$ to $n=3$.
4. The electron spirals inward continuously from $n=4$ to $n=1$.

Explanation: This question examines the Bohr model of atomic structure. In the Bohr model, the energy of emitted photons equals the difference between initial and final energy levels, and larger energy differences produce higher-energy photons. Since energy levels get closer together as n increases, the largest possible energy difference occurs when an electron drops from the highest level (n=4) to the lowest level (n=1). This n=4 to n=1 transition produces the highest-energy photon possible in this system. Choices B and C represent smaller energy differences and thus lower-energy photons, while choice D violates the quantization principle by suggesting continuous motion between levels. The key principle: maximum photon energy comes from the largest allowed energy level difference.

Question 7

1. It radiates continuously, so it slowly spirals into the nucleus.
2. It can have any energy, so it avoids radiating by choosing a continuous orbit.
3. It does not radiate energy while in an allowed orbit. (correct answer)
4. It is held by gravity, so radiation is unnecessary for stability.

Explanation: This question examines the Bohr model of atomic structure. According to Bohr's postulates, electrons in allowed orbits (n = 1, 2, 3) do not radiate energy despite their circular motion, which contradicts classical physics. This stability in allowed orbits is a fundamental assumption that prevents electrons from spiraling into the nucleus. Electrons only emit or absorb photons when transitioning between allowed levels, not while remaining in a single orbit. Choice A represents the classical physics prediction that Bohr's model specifically addresses, choice B incorrectly suggests continuous energy values, and choice D incorrectly invokes gravity instead of electromagnetic forces. The key principle: electrons in allowed Bohr orbits are stable and do not radiate energy.

Question 8

1. It loses energy and spirals into the nucleus slowly
2. It does not radiate while in an allowed orbit (correct answer)
3. It can occupy any orbit radius without losing energy
4. It radiates continuously but cannot reach the nucleus

Explanation: This question tests understanding of the Bohr model of atomic structure. The Bohr model postulates that electrons in allowed orbits do not radiate electromagnetic energy, solving the classical physics problem where accelerating charges must radiate. In classical physics, an orbiting electron would continuously lose energy and spiral into the nucleus, but Bohr's model prevents this by stating that electrons in quantized orbits are stable and do not radiate. The electron only emits or absorbs photons when transitioning between allowed levels. Choice D represents the classical misconception that electrons must continuously lose energy while orbiting. Remember that Bohr's key innovation was proposing stable, non-radiating orbits at specific energy levels.

Question 9

1. The electron moves from $n=4$ to $n=3$ only
2. The electron moves from $n=4$ to $n=2.7$ smoothly
3. The electron moves from $n=4$ to $n=1$ only (correct answer)
4. The electron spirals from $n=4$ toward the nucleus continuously

Explanation: This question tests understanding of the Bohr model of atomic structure. In the Bohr model, electrons can only occupy discrete energy levels, and photon energy equals the energy difference between levels. The highest-energy photon is produced by the largest energy drop, which occurs when the electron falls to the lowest possible level. From n=4, the largest drop is to n=1, producing a photon with energy proportional to the difference between these levels. Choice C incorrectly suggests the electron can move to n=2.7, violating the principle that only integer values of n are allowed in the Bohr model. To find the highest-energy photon, always look for the transition with the largest change in n value.

Question 10

1. The electron changes from $E_2$ to $E_3$ by absorbing a photon.
2. The electron changes from $E_3$ to $E_1$ by emitting a photon.
3. The electron changes from $E_2$ to an energy between $E_2$ and $E_3$. (correct answer)
4. The electron changes from $E_1$ to $E_2$ by absorbing a photon.

Explanation: This question tests the Bohr model of atomic structure. In Bohr's theory, electrons can only occupy discrete energy levels (E₁, E₂, E₃), and any energy between these levels is forbidden. Therefore, a transition to an energy between E₂ and E₃ (choice C) is impossible because it would place the electron at a forbidden energy. All other transitions shown (A, B, and D) involve jumps between allowed levels with appropriate photon absorption or emission. Choice A shows upward transition with absorption, choice B shows downward transition with emission, and choice D shows upward transition with absorption - all physically allowed. Remember: electrons cannot exist at energies between allowed levels.

Question 11

1. Lower $n$ occurs when a photon is absorbed and energy increases
2. Any $n$ occurs because energies are continuous and unrestricted
3. Higher $n$ occurs when a photon is absorbed and energy increases (correct answer)
4. Higher $n$ occurs when a photon is emitted and energy decreases

Explanation: This question tests understanding of the Bohr model of atomic structure. In the Bohr model, the relationship between orbit changes and photon behavior follows strict rules based on energy conservation and quantization. When an electron absorbs a photon, it gains energy and moves to a higher energy level (larger n value), moving farther from the nucleus. Conversely, when an electron emits a photon, it loses energy and falls to a lower level (smaller n value). The photon energy always equals the exact energy difference between the two levels. Choice D incorrectly suggests energies are continuous, which represents the classical misconception that Bohr's model rejects through quantization. The key principle is that absorption always increases n (and energy) while emission always decreases n.

Question 12

1. An electron moves to an orbit between $n=2$ and $n=3$
2. An electron moves from $n=3$ to $n=2$ (correct answer)
3. An electron moves from $n=2$ to $n=3$
4. An electron spirals continuously into the nucleus

Explanation: This question tests understanding of the Bohr model of atomic structure. In the Bohr model, electrons can only occupy specific, quantized energy levels (n=1, 2, 3, 4, etc.), and transitions between these levels involve the emission or absorption of photons. When an electron moves from a higher energy level to a lower one, it must release energy in the form of a photon emission. Conversely, moving from a lower to higher level requires absorbing a photon. Choice C incorrectly suggests continuous spiraling, which violates the quantized nature of Bohr orbits—this represents the classical physics misconception that led to the ultraviolet catastrophe. The key strategy is to remember that photon emission always accompanies transitions from higher n to lower n values.

Question 13

1. An electron transitions from $n=2$ to $n=5$.
2. An electron transitions from $n=5$ to $n=2$. (correct answer)
3. An electron transitions from $n=3$ to an energy between $n=2$ and $n=3$.
4. An electron spirals inward continuously from $n=5$ to the nucleus.

Explanation: This question addresses the Bohr model of atomic structure. In the Bohr model, photon emission occurs when an electron transitions from a higher allowed energy level to a lower allowed energy level. The transition from n=5 to n=2 represents a downward jump between allowed states, releasing energy as a photon with energy equal to E₅ - E₂. This is the fundamental emission process in the Bohr model. Choice C incorrectly suggests the electron can occupy an energy between allowed levels, which violates the quantization principle that defines the Bohr model. The key rule is that emission requires downward transitions between discrete allowed levels.

Question 14

1. The electron moves from $n=3$ to $n=2$. (correct answer)
2. The electron moves from $n=2.5$ to $n=2$.
3. The electron spirals continuously inward toward the nucleus.
4. The electron moves from $n=3$ to $n=3.2$.

Explanation: This question tests understanding of the Bohr model of atomic structure. In Bohr's model, electrons can only exist in specific, quantized energy levels (n = 1, 2, 3, etc.) and cannot exist between these levels. When an electron transitions from a higher energy level to a lower one, it emits a photon with energy equal to the difference between the two levels. The transition from n=3 to n=2 (choice A) represents a drop to a lower energy state, resulting in photon emission. Choice B is impossible because n=2.5 is not an allowed level, choice C violates the quantization principle by suggesting continuous motion, and choice D shows an upward transition that would require photon absorption, not emission. Remember: photon emission occurs only when electrons jump down to lower allowed levels.

Question 15

1. $E_3-E_1$ (correct answer)
2. $E_1-E_3$
3. Any value between $E_3-E_2$ and $E_2-E_1$
4. Zero, because electrons cannot change energy in this model

Explanation: This question examines the Bohr model of atomic structure. When an electron transitions between allowed energy levels in the Bohr model, it must emit or absorb a photon with energy exactly equal to the difference between the levels. For a downward transition from E₃ to E₁, the electron loses energy, emitting a photon with energy E₃ - E₁ (since E₃ > E₁). This represents the energy conservation principle in quantum transitions. Choice B gives a negative value since E₁ < E₃, choice C incorrectly suggests variable photon energies, and choice D contradicts the fundamental premise that electrons can change levels. The key principle: emitted photon energy equals the positive difference between initial and final energy levels.

Question 16

1. An electron moves from $n=4$ to $n=2$ with photon emission
2. An electron moves from $n=2$ to $n=4$ with photon absorption
3. An electron remains in $n=3$ without radiating energy
4. An electron occupies an energy between $n=1$ and $n=2$ (correct answer)

Explanation: This question tests understanding of the Bohr model of atomic structure. The fundamental principle of the Bohr model is that electrons can only exist in specific, quantized energy levels—they cannot occupy energies between these allowed states. Options A, B, and C all describe permitted processes: downward transitions with emission, upward transitions with absorption, and stable occupation of an allowed level without radiation. However, an electron occupying an energy between allowed levels violates the core quantization principle. Choice D represents the classical misconception that energy can vary continuously, which the Bohr model specifically prohibits. The key rule is that electrons must always be in one of the allowed energy levels, never between them.

Question 17

1. The electron spreads into a continuum of orbit radii
2. The electron spirals into the nucleus after absorbing energy
3. The electron moves to $n=3$ in a single jump (correct answer)
4. The electron moves to $n=2.4$ and stays there

Explanation: This question tests understanding of the Bohr model of atomic structure. In the Bohr model, electrons can only exist in discrete energy levels with integer quantum numbers n. When an electron at n=2 absorbs energy, it must absorb exactly the right amount to reach another allowed level like n=3; it cannot stop at intermediate positions like n=2.4. The electron makes an instantaneous quantum jump to the new level without passing through forbidden intermediate states. Choice B incorrectly suggests the electron can remain at n=2.4, which violates the fundamental quantization principle. Remember that only discrete energy levels with integer n values are allowed in the Bohr model.

Question 18

1. The electron moves from $n=4$ to $n=3$ only (correct answer)
2. The electron shifts continuously to any orbit radius
3. The electron spirals inward while radiating at all frequencies
4. The electron moves from $n=4$ to $n=5$ only

Explanation: This question tests understanding of the Bohr model of atomic structure. In the Bohr model, electrons can only occupy specific energy levels, and photon emission occurs when an electron transitions from a higher to a lower energy level. From n=4, the electron can emit a photon by dropping to n=3, n=2, or n=1, but not by moving up to n=5 (which would require absorption). The emitted photon carries away the exact energy difference between the initial and final levels. Choice C incorrectly suggests the electron can shift to any orbit radius, violating the quantization principle. To identify emission, look for transitions from higher to lower n values.

Question 19

1. The atom must absorb a photon with energy $E_4-E_2$. (correct answer)
2. The atom must emit a photon with energy $E_4-E_2$.
3. The electron passes through all intermediate energies continuously.
4. The electron spirals outward while radiating energy continuously.

Explanation: This question tests the Bohr model of atomic structure. In Bohr's theory, electrons occupy only discrete energy levels, and transitions between levels require the absorption or emission of photons with specific energies. To move from n=2 to n=4, the electron must jump to a higher energy level, which requires absorbing a photon with energy exactly equal to E₄ - E₂. The electron cannot exist at intermediate energies between allowed levels, making instantaneous transitions necessary. Choice B incorrectly suggests emission during an upward transition, while choices C and D violate the quantization principle by proposing continuous energy changes. Remember: upward transitions require photon absorption with energy matching the level difference.

Question 20

1. It is stable because the electron cannot radiate while remaining in an allowed orbit. (correct answer)
2. It is stable because the electron continuously loses energy but never reaches the nucleus.
3. It is stable because the electron may occupy any radius between $n=1$ and $n=2$.
4. It is stable because the nucleus exerts no force on electrons in circular motion.

Explanation: This question examines the Bohr model of atomic structure. The Bohr model postulates that electrons in allowed orbits do not radiate energy, which solves the classical physics problem of accelerating charges losing energy through radiation. The n=1 level represents the ground state, the lowest allowed energy level where the electron is stable because it cannot transition to any lower state. While in this allowed orbit, the electron does not radiate energy despite its circular motion, which would classically require acceleration. Choice B incorrectly suggests the electron continuously loses energy, which contradicts Bohr's postulate of stable orbits. The key principle is that electrons in allowed orbits are stable and do not radiate energy.