IB Physics SL E.1 Structure of the atom Questions

SLSL HLHL

Practise IB Physics SL E.1 by modelling nuclei, isotopes, spectra, binding energy and the evidence for atomic structure.

65 questions in this syllabus scope, with question parts counted together.

Exam points & syllabus

Exam points

Describe scattering observations with relative frequencies and link them to mostly empty atoms with small, dense, positively charged nuclei.
State the historical nuclear model with concentrated mass and charge, and distinguish its supported claims from electron-level or orbit claims.
Use A=Z+N in nuclide notation, reading A above Z and finding neutrons from A−Z rather than confusing nucleon and proton numbers.
Exclude electrons from nucleon counts: an ion’s extra electrons change its charge but not A, Z or nuclear identity.
Balance A and Z independently to identify unknown reaction nuclei or particles; supply both numbers when the marking point requires them together.
Include incident neutrons and outgoing coefficients when balancing fission, and keep the assumed parent isotope consistent with the neutron count.
For alpha decay, obtain the daughter proton number by subtracting two from the parent rather than confusing the mass change with the charge change.
Describe observing absorption by passing white light through a gas and analysing the transmitted light; the result is dark lines on a continuous background.
Explain line-spectrum evidence through specific photon frequencies, E=hf and electron-energy differences, rather than simply saying levels are discrete.
Identify electrons as the atomic-transition particles; emission is a downward energy change releasing a photon, while absorption raises the atomic energy.
Test absorption against an allowed gap from the specified initial state; being below ionization energy does not by itself make a photon absorbable.
Draw the particular downward transition matching a photon’s energy and use the actual diagram labels rather than a corrupted flattened index.
Count all accessible downward pairs, including intermediate transitions, while excluding levels above the specified excitation and checking distinct gaps.
When a spectral count has a strict energy threshold, calculate each candidate gap and exclude a transition exactly equal to that threshold.
Use E=hf=hc/λ with consistent units; subtract levels before converting eV to joules, and convert wavelength prefixes before substitution.
For a longest wavelength or lowest frequency, choose the smallest allowed positive gap; shortest wavelength corresponds to the largest relevant gap.
From an absorbed wavelength, compute hc/λ and identify both matching endpoint states; in a show-that emission task also demonstrate the matching gap.
Relate spectrum positions to level gaps through the wavelength axis, including combined gaps and the possibility that only part of the spectrum is shown.
Use spectra as evidence for changes in atomic modelling and distinguish this evidence for energy levels from scattering or nuclear reactions.
Determine chemical composition by comparing observed element-specific stellar lines with laboratory spectra, explaining selective absorption when required.
Use matching stellar dips and hydrogen emission peaks as evidence of hydrogen, while keeping an inferred main-sequence classification conditional.
Confirm solar helium through observed lines matching helium; a proposed fusion model alone is not the requested empirical confirmation.

Covered syllabus points

E.1.1—Rutherford experiment E.1.2—Nuclear notation E.1.3—Atomic energy levels E.1.4—Atomic transitions E.1.5—Photon energy E.1.6—Spectra and composition

Exam points

Describe observations with their relative frequencies: most alpha particles pass through undeflected, some deviate and a few scatter back.
Link observations to conclusions: mostly undeflected particles imply empty space, while rare large deflections imply a small, dense, positive nucleus.
Describe Rutherford’s nuclear model with mass and positive charge concentrated in a small nucleus and electrons outside it; identify it as a model.
Distinguish tested claims: scattering falsifies volume-filling positive charge but does not establish discrete electron energy levels or fixed-radius orbits.

[Maximum number: 4]

This question is in two parts. Part 1 is about the nuclear model of the atom and radioactive decay. Part 2 is about waves.

Part 1 Nuclear model of the atom and radioactive decay

Outline how the evidence supplied by the Geiger-Marsden experiment supports the nuclear model of the atom.

Exam points

Read and write nuclide notation with nucleon number A above proton number Z; use A=Z+N and N=A−Z to count neutrons.
Count only protons and neutrons in A; changing an atom’s electron count or ion charge does not change its nuclear notation.
Balance nucleon and proton numbers separately in a nuclear equation and give both missing values when the mark requires them together.
Identify an unknown reaction particle from its A and Z, distinguishing proton, neutron and alpha particle rather than relying on the reaction’s name.
For alpha decay, subtract two from the parent proton number to obtain the daughter’s proton number.
In a fission equation, include the incident neutron in nucleon balance and keep the emitted neutron count consistent with the chosen parent isotope.

[Maximum number: 1]

Tritium may be produced by bombarding a nucleus of the isotope lithium-7 with a high-energy neutron. The reaction equation for this interaction is

{ }_{3}^{7} \mathrm{Li}+{ }_{0}^{1} \mathrm{n} \rightarrow{ }_{1}^{3} \mathrm{H}+{ }_{Z}^{4} \mathrm{X}+{ }_{0}^{1} \mathrm{n} .

Identify the proton number Z of X.

Exam points

Produce an absorption spectrum by passing white light through the gas and then observing the transmitted light with a spectroscope, grating or prism.
Describe absorption as dark lines across a continuous spectrum, rather than bright isolated lines or a uniformly dimmer continuum.
Explain emission lines through downward electron transitions: discrete energy gaps give discrete photon energies and therefore discrete frequencies.
For absorption, link each missing wavelength to a photon whose energy matches a difference between allowed atomic states.
Count all distinct allowed downward transitions in the supplied energy-level diagram, including cascades; do not count only adjacent or ground-state drops.
Identify atomic spectra as evidence that changed atomic modelling; distinguish energy-level evidence from scattering, fission or radioactive decay.

[Maximum number: 7]

This question is about atomic energy levels.

(a)

Outline a laboratory procedure for producing and observing the atomic absorption spectrum of a gas.

[ 3 ]

(b)

Describe the appearance of an atomic absorption spectrum.

[ 1 ]

(c)

Explain why the spectrum in (a) provides evidence for quantization of energy in atoms.

[ 3 ]

Exam points

Identify electrons as the particles changing atomic energy level; emission lowers the atom’s energy and releases a photon.
For absorption, choose an upward transition whose energy gap exactly matches the incident photon, not a downward transition with the same magnitude.
Use the specified initial state when testing absorption; a photon below ionization energy is not absorbed unless it matches an allowed gap from that state.
Draw emission arrows downwards between the two levels whose difference equals the given photon energy, using the actual diagram labels.
Count all accessible downward transitions, including intermediate drops, but exclude levels above the stated excitation and avoid counting only adjacent levels.
When counting photons above an energy threshold, calculate each candidate gap and apply the strict inequality; an equal-energy transition does not qualify.
Convert an absorbed wavelength with hc/λ, change joules to eV if needed and identify both initial and final levels matching the positive energy gap.
Compare frequencies through energy gaps and wavelengths inversely: the largest downward gap gives the highest frequency and shortest wavelength.
Use ΔE=hf on the supplied level gaps to find possible frequencies; include combined gaps when deciding which frequencies are smallest.
Match spectral lines to energy gaps using the wavelength axis correctly; a question showing part of a spectrum need not show every possible line.

[Maximum number: 4]

This question is about energy level transitions.

Some of the electron energy levels for a hydrogen atom are shown.

(a)

A hydrogen atom is excited to the -1.51 eV level.

[ 1 ]

(i)

On the diagram, label using arrows all the possible transitions that might occur as the hydrogen atom returns to the ground state.

[ 1 ]

only the three correct arrows on diagram;

(-1.51 \text { to }-3.40,-1.15 \text { to }-13.6 \text { and }-3.40 \text { to }-13.6)

(b)

Monochromatic radiation is incident on gaseous hydrogen. All the hydrogen atoms are in the ground state. Describe what could happen to the radiation and to the hydrogen atoms if the incident photon energy is equal to

[ 3 ]

(i)

10.2 eV .

[ 2 ]

(ii)

9.0 eV .

[ 1 ]

Exam points

Calculate photon energy using E=hf=hc/λ, selecting the stated spectral wavelength and converting nanometres to metres before substitution.
Use a positive difference between the two given level energies, not an absolute negative level, and convert eV to joules before using SI h and c.
For longest wavelength choose the smallest accessible emission gap; for shortest wavelength choose the largest transition actually shown or allowed.
Find the lowest possible absorption frequency from the smallest positive allowed energy gap divided by h, respecting any stated initial-state condition.
To show that a wavelength can be emitted, calculate its photon energy and match that value to a specific downward gap in the supplied level diagram.

[Maximum number: 1]

This question is about energy level transitions.

Some of the electron energy levels for a hydrogen atom are shown.

A hydrogen atom is excited to the -1.51 eV level.

State the energy in eV of the maximum wavelength photon emitted as the hydrogen atom returns to the ground state.

Exam points

Obtain the star’s line spectrum and compare its element-specific absorption wavelengths with known laboratory spectra to identify the elements present.
Match stellar absorption dips with laboratory hydrogen emission peaks as evidence of hydrogen; treat any stellar-type inference as a suggestion.
Confirm helium in the Sun empirically by identifying solar spectral lines matching helium, rather than relying only on a proposed fusion reaction.

[Maximum number: 2]

The diagram shows a simplified energy-balance model for the Earth surface–atmosphere system.

The following data are given:

\begin{aligned} \text { Average albedo of Earth } & =0.30 \\ \text { Average global temperature of the surface } & =288 \mathrm{~K} \\ \text { Average Earth-Sun distance } & =1.5 \times 10^{11} \mathrm{~m} \end{aligned}

The primary energy source of the Sun is the proton-proton (p-p) chain of fusion reactions. Four protons and two electrons produce a helium nucleus together with neutrinos and gamma photons. The overall reaction is:

4{ }_{1}^{1} \mathrm{p}+2{ }_{-1}^{0} \mathrm{e} \rightarrow{ }_{2}^{4} \mathrm{He}+2{ }_{0}^{0} v_{e}+4 \gamma

Outline how the presence of helium in the Sun can be confirmed empirically.

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