E.1 Structure of atom
Practice exam-style IB Physics questions for Structure of atom, aligned with the syllabus and grouped by topic.
Question 1
A neutral atom is represented by . How many neutrons does the nucleus contain?
A.
18
B.
40
C.
22
D.
58
Question 2
In the Geiger–Marsden–Rutherford experiment, a very small number of alpha particles were scattered through angles greater than 90°. What conclusion follows from this observation?
A.
Electrons contain most of the mass of the atom.
B.
The positive charge of the atom is spread uniformly throughout its volume.
C.
The atom contains a small, dense, positively charged nucleus.
D.
Alpha particles are negatively charged.
Question 3
A low-pressure gas is placed in front of a continuous source of white light. The spectrum observed after the light passes through the gas contains dark lines. What type of spectrum is observed?
A.
Absorption line spectrum
B.
Continuous spectrum
C.
Emission line spectrum
D.
Diffraction spectrum
Question 4
An atom changes from a lower energy level to a higher energy level. What must occur?
A.
The atom emits a continuous range of photon energies.
B.
A photon with energy equal to the level difference is absorbed.
C.
A photon with any energy less than the level difference is absorbed.
D.
A photon with energy equal to the level difference is emitted.
Question 5
Two nuclei have nucleon numbers and . What is the ratio of their radii, ?
A.
27
B.
1
C.
3
D.
9
Question 6
Alpha particles are incident on a thin metal foil in a Rutherford scattering experiment.
State one observation for most alpha particles.
[1]
State the surprising observation for a very small fraction of alpha particles.
[1]
Outline the inference made about the atom from the surprising observation.
[1]
Question 7
A nucleus is represented by .
State the number of protons.
[1]
Determine the number of neutrons.
[1]
State the number of electrons in the neutral atom.
[1]
Question 8
An atom emits a photon of frequency . What is the energy of the photon?
A.
$3.3 imes10^{-19}\, ext{J}$
B.
$7.5 imes10^{47}\, ext{J}$
C.
$3.0 imes10^{8}\, ext{J}$
D.
$1.3 imes10^{-48}\, ext{J}$
Question 9
Why can an emission spectrum be used to identify an element in a gas sample?
A.
Each element emits all visible wavelengths with equal intensity.
B.
Each element emits photons only from its nucleus.
C.
Each element has the same spectrum at low pressure.
D.
Each element has a distinctive pattern of allowed energy differences.
Question 10
The same gas is used to produce an emission spectrum and an absorption spectrum. How are the wavelengths of the bright emission lines related to the wavelengths of the dark absorption lines?
A.
They are the same for transitions between the same energy levels.
B.
The absorption wavelengths form a continuous range.
C.
They are unrelated because absorption involves electrons only.
D.
The emission wavelengths are always half the absorption wavelengths.
Question 11
In the model , what is the approximate dependence of nuclear density on nucleon number ?
A.
It is approximately independent of $A$.
B.
It is proportional to $A^{1/3}$.
C.
It is proportional to $A^{-1}$.
D.
It is proportional to $A$.
Question 12
Rutherford scattering predictions fail at sufficiently high alpha-particle energies. What is the main reason?
A.
The alpha particles become electrically neutral.
B.
The target nuclei lose all their protons.
C.
The electrons in the atom cause all large-angle scattering.
D.
The alpha particles approach close enough for the strong nuclear interaction to affect them.
Question 13
What is the energy of the level in hydrogen according to the Bohr model?
A.
$-54.4\, ext{eV}$
B.
$-13.6\, ext{eV}$
C.
$+3.40\, ext{eV}$
D.
$-3.40\, ext{eV}$
Question 14
What is Bohr’s quantization condition for the angular momentum of an electron in a hydrogen orbit?
A.
$mv^2/r=nh/2\pi$
B.
$hf=nh/2\pi$
C.
$mvr=nh/2\pi$
D.
$mvr=h/2\pi n$
Question 15
A low-pressure gas produces a spectrum consisting of bright lines on a dark background.
Name this type of spectrum.
[1]
Explain why this spectrum provides evidence for discrete atomic energy levels.
[1]
Question 16
An atom emits a photon during a transition of energy .
Calculate the frequency of the photon.
[1]
State how the frequency would change for a larger energy gap.
[1]
Question 17
Distinguish between an emission line spectrum and an absorption line spectrum. [2]
Question 18
A nucleus has nucleon number . Use .
Calculate its nuclear radius.
[1]
State one assumption in the model .
[1]
Question 19
A student counts scintillations at different scattering angles in an alpha-particle scattering experiment using a thin gold foil.
State the general trend shown by the count rate as scattering angle increases.
[1]
Identify the observation that is not explained by the Thomson model.
[1]
Explain what this observation implies about the distribution of positive charge in the atom.
[1]
Question 20
The table gives information for four neutral atoms. Some entries are missing.
| Atom | Proton number Z | Nucleon number A | Neutron number N | Electrons |
|---|---|---|---|---|
| P | 8 | 18 | ? | 8 |
| Q | 12 | ? | 13 | 12 |
| R | 8 | 16 | 8 | 8 |
| S | 14 | 29 | 15 | 14 |
Determine the missing neutron number for isotope P.
[1]
Determine the missing nucleon number for isotope Q.
[1]
Identify the two isotopes of the same element.
[1]
Explain your answer to (c).
[1]
Question 21
A photon emitted by an atom has energy . What is its wavelength? Use .
A.
$5.0 imes10^{-7}\, ext{m}$
B.
$3.1 imes10^{-6}\, ext{m}$
C.
$2.0 imes10^{-6}\, ext{m}$
D.
$8.1 imes10^{5}\, ext{m}$
Question 22
In a head-on alpha-particle scattering experiment with a fixed target nucleus, the alpha-particle kinetic energy is doubled. What happens to the distance of closest approach, assuming only electric repulsion?
A.
It is unchanged.
B.
It is halved.
C.
It is reduced by a factor of four.
D.
It is doubled.
Question 23
A hydrogen atom makes a transition from to . What is the photon energy?
A.
$1.89\, ext{eV}$
B.
$12.1\, ext{eV}$
C.
$4.91\, ext{eV}$
D.
$3.40\, ext{eV}$
Question 24
In the de Broglie interpretation of Bohr orbits, what condition must an allowed circular orbit satisfy?
A.
The electron emits radiation continuously as it moves.
B.
The electron speed is equal to the speed of light.
C.
An integer number of electron wavelengths fits around the circumference.
D.
The electron wavelength is larger than the diameter of the atom.
Question 25
A spectral line has wavelength .
Calculate the photon energy in eV. Use .
[1]
State whether this photon could be absorbed by an atom if no allowed energy gap has this value.
[1]
Explain your answer to (b).
[1]
Question 26
The spectrum of a star contains dark lines that match some laboratory lines for hydrogen.
Suggest what this indicates about the outer layers of the star.
[1]
Explain why a laboratory spectrum can be used for this comparison.
[1]
Question 27
Use the relationship to explain why nuclear density is approximately independent of nucleon number. [3]
Question 28
Rutherford scattering of alpha particles by a target nucleus agrees with a purely electric model at low energies but not at sufficiently high energies.
State what happens to the distance of closest approach when the alpha-particle energy is increased.
[1]
Explain why deviations from Rutherford scattering can then occur.
[1]
Question 29
For hydrogen, .
Calculate the energy of the level.
[1]
Calculate the energy of the photon emitted in a transition from to .
[1]
State the spectral region for transitions ending at .
[1]
Question 30
The Bohr model describes stationary states in hydrogen.
State what is meant by the ground state of hydrogen.
[1]
Explain why the bound-state energies in the Bohr model are negative.
[1]
Question 31
An energy-level diagram for an atom is shown. Three downward transitions are labelled P, Q and R.
Identify the transition that emits the highest-frequency photon.
[1]
Identify the transition that emits the longest-wavelength photon.
[1]
Explain your answers to
[1]
and (b).
[1]
State why only three spectral lines are shown rather than a continuous spectrum.
[1]
Question 32
A spectrum from an unknown low-pressure gas is compared with reference spectra for three elements.
Identify which element is present in the unknown gas.
[1]
State the evidence for your answer.
[1]
Suggest why not every line in the unknown spectrum needs to match this one element.
[1]
Explain why line spectra can be used as chemical fingerprints.
[1]
Question 33
Data for several nuclei are plotted as nuclear radius against .
State what the straight-line graph indicates about the relationship between and .
[1]
Determine from the gradient of the graph.
[1]
Explain why this relationship implies that nuclear volume is proportional to .
[1]
State the implication for nuclear density.
[1]
Question 34
A beam containing all visible wavelengths passes through a cool low-pressure gas. Some wavelengths are missing from the transmitted beam.
Explain why only some wavelengths are absorbed.
[1]
Explain why the missing wavelengths appear dark when viewed in the original direction, even though photons may later be emitted.
[1]
Question 35
An alpha particle of kinetic energy is incident head-on on a nucleus with proton number . Assume only electric repulsion. Use and .
State the charge of the alpha particle.
[1]
Calculate the distance of closest approach.
[1]
Question 36
In the Bohr model, the angular momentum of an electron in a hydrogen atom is quantized.
State Bohr’s angular momentum condition.
[1]
Explain how the de Broglie standing-wave picture leads to this condition.
[1]
Question 37
Discuss two limitations of the Bohr model of the atom. [4]
Question 38
A graph shows photon energy plotted against frequency for light emitted by several atomic transitions.
State the relationship shown by the graph.
[1]
Determine Planck’s constant from the gradient of the graph.
[1]
Suggest one reason why a measured point may not lie exactly on the best-fit line.
[1]
Explain how the graph supports the photon model of light.
[1]
Question 39
The graph shows the measured number of alpha particles scattered at each angle for two incident kinetic energies, together with the Rutherford prediction.
State which energy agrees better with Rutherford scattering.
[1]
Identify the angle region where deviations are most evident.
[1]
Explain why the higher-energy data deviate from the prediction.
[1]
Suggest what information can be obtained from the energy at which deviations begin.
[1]
Question 40
A table gives the distance of closest approach for alpha particles incident head-on on the same target nucleus at different kinetic energies.
| Kinetic energy / MeV | Closest approach / m |
|---|---|
| 4.0 | 5.69 × 10^-14 |
| 5.0 | 4.55 × 10^-14 |
| 6.0 | 3.79 × 10^-14 |
| 7.0 | 3.25 × 10^-14 |
| 8.0 | 2.84 × 10^-14 |
Describe the relationship between distance of closest approach and alpha-particle kinetic energy.
[1]
Use one row of the table to determine the proton number of the target nucleus.
[1]
Explain why the calculated distance is not a direct measurement of the nuclear radius.
[1]
Question 41
The diagram shows the first five energy levels of hydrogen calculated using .
Identify the transition shown that emits the shortest wavelength.
[1]
Calculate the photon energy for the transition from to .
[1]
Determine whether the photon in
[1]
is in the Balmer series.
[1]
Explain why the energy levels get closer together as increases.
[1]
Question 42
The Geiger–Marsden–Rutherford experiment led to a change in the model of the atom.
Outline the experimental arrangement and the main observations.
[1]
Discuss how these observations led to the nuclear model of the atom and why they were inconsistent with the Thomson model.
[1]
Question 43
Line spectra are evidence for discrete atomic energy levels.
Distinguish between an emission line spectrum and an absorption line spectrum.
[1]
Explain how emission and absorption spectra arise from atomic transitions and why the same gas can have matching emission and absorption wavelengths.
[1]
Question 44
An atom has two energy levels separated by .
Calculate the frequency of a photon emitted during a transition between these levels.
[1]
Explain, using this example, the conditions for photon emission and absorption in atoms.
[1]
Question 45
A simulation shows electron waves around circular hydrogen orbits. Some waves join smoothly after one circuit and others do not.
Identify which orbit is allowed by the standing-wave condition.
[1]
State the standing-wave condition for an allowed orbit.
[1]
Show how this condition leads to angular momentum quantization.
[1]
Suggest one reason why the Bohr model is not a complete model of atoms.
[1]
Question 46
Spectra from stars can be used to infer physical information without collecting samples.
Outline how a spectrometer can identify chemical elements in a star.
[1]
Evaluate the use of stellar spectra for determining composition and other properties of stars.
[1]
Question 47
Nuclear radius measurements are described by .
Calculate the radius of a nucleus with using .
[1]
Evaluate the implication of this relationship for nuclear volume and density.
[1]
Question 48
An alpha particle is fired head-on at a stationary nucleus of proton number .
Derive the expression for the distance of closest approach, , assuming only electric repulsion.
[1]
Discuss how changing the alpha-particle energy and target proton number affects , and why deviations from Rutherford scattering may occur at high energies.
[1]
Question 49
The Bohr model gives the hydrogen energy levels as .
Calculate the wavelength of the photon emitted for the transition from to . Use .
[1]
Explain the physical meaning of negative energy levels and the convergence of the levels at high .
[1]
Question 50
Bohr’s model introduced quantized orbits for hydrogen.
State the angular momentum quantization condition and the corresponding de Broglie standing-wave condition.
[1]
Compare and contrast the successes and limitations of the Bohr model for explaining atomic spectra.
[1]
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