IB Physics SL E.1 Structure of the atom questions

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Question 1

Multiple choiceEasy1 mark

A nucleus is represented by ZAX{}^{A}_{Z}X A second nucleus has the same proton number but one more neutron. What is its nuclear notation?

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Answer: A. AA is the nucleon number and ZZ is the proton number. One additional neutron increases the nucleon number by 1 while leaving the proton number, and therefore the element XX unchanged. The notation is ZA+1X{}^{A+1}_{Z}X

B: increases the proton number while keeping the nucleon number unchanged. C: decreases the nucleon number, corresponding to one fewer neutron at the same proton number. D: increases both the proton and nucleon numbers, adding a proton as well as a neutron.

Remember: adding a neutron changes AA not ZZ

Question 2

Paper 2Easy6 marks

Figure 1 shows nuclear notation and schematic emission and absorption spectra for an element.

2311Xemission spectrumabsorption spectrum400450500550wavelength / nm
(a)

In the nuclear notation shown in Figure 1, state what AA and ZZ represent, and calculate the number of neutrons in the nucleus.

[3]
(b)

Describe one feature of the line positions in the spectra shown in Figure 1.

[1]
(c)

Explain how the spectra provide evidence that atomic energy levels are discrete.

[2]

Question 3

Multiple choiceMedium1 mark

An atom emits a photon during the transition shown in the energy-level diagram. Take h=6.6×10−34 J sh=6.6\times10^{-34}\,\text{J s} and c=3.0×108 m s−1c=3.0\times10^8\,\text{m s}^{-1} What is the wavelength of the emitted photon?

Energy, E / J5.0×10−19 J4.0×10−19 J3.0×10−19 J2.0×10−19 J1.0×10−19 J0 J0 J1.1×10−19 J4.4×10−19 J
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Answer: C. The photon energy equals the difference between the atomic energy levels. Using E=hfE=hf and c=fλc=f\lambda λ=hc/ΔE\lambda=hc/\Delta E

  1. ΔE=(4.4−1.1)×10−19=3.3×10−19 J\Delta E=(4.4-1.1)\times10^{-19}=3.3\times10^{-19}\,\text{J}
  2. λ=(6.6×10−34)(3.0×108)3.3×10−19=6.0×10−7 m\lambda=\frac{(6.6\times10^{-34})(3.0\times10^8)}{3.3\times10^{-19}}=6.0\times10^{-7}\,\text{m}

A: adds the two level energies instead of finding their difference.
B: uses the upper level’s energy relative to zero rather than the energy gap shown.
D: uses the lower level’s energy as the photon energy rather than the difference between the levels.

Remember: a spectral line corresponds to a photon with energy equal to the difference between two discrete atomic energy levels.

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