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title: "A student analyzes the photoelectron spectra (PES) of gaseous magnesium, \\(\\text{Mg}\\), and aluminum, \\(\\text{Al}\\). The student observes that the peak corresponding to the lowest binding energy for \\(\\text{Al}\\) occurs at a lower energy than the peak corresponding to the lowest binding energy for \\(\\text{Mg}\\). To support the claim that this difference is caused by the shielding and higher energy of the \\(3p\\) subshell in \\(\\text{Al}\\), rather than a weaker effective nuclear charge experienced by the \\(n = 3\\) valence shell overall, which of the following pieces of evidence from the PES data is most decisive?"
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url: "https://nerd-notes.com/ubq/120165/"
date_modified: "2026-08-21T16:02:42+00:00"
---

# A student analyzes the photoelectron spectra (PES) of gaseous magnesium, \(\text{Mg}\), and aluminum, \(\text{Al}\). The student observes that the peak corresponding to the lowest binding energy for \(\text{Al}\) occurs at a lower energy than the peak corresponding to the lowest binding energy for \(\text{Mg}\). To support the claim that this difference is caused by the shielding and higher energy of the \(3p\) subshell in \(\text{Al}\), rather than a weaker effective nuclear charge experienced by the \(n = 3\) valence shell overall, which of the following pieces of evidence from the PES data is most decisive?

A student analyzes the photoelectron spectra (PES) of gaseous magnesium, \(\text{Mg}\), and aluminum, \(\text{Al}\). The student observes that the peak corresponding to the lowest binding energy for \(\text{Al}\) occurs at a lower energy than the peak corresponding to the lowest binding energy for \(\text{Mg}\). To support the claim that this difference is caused by the shielding and higher energy of the \(3p\) subshell in \(\text{Al}\), rather than a weaker effective nuclear charge experienced by the \(n = 3\) valence shell overall, which of the following pieces of evidence from the PES data is most decisive?

- **A.** The observation that the \(3s\) peak for \(\text{Al}\) appears at a higher binding energy than the \(3s\) peak for \(\text{Mg}\), indicating that the \(3s\) electrons experience a greater effective nuclear charge in \(\text{Al}\).
- **B.** The observation that the \(3s\) peak for \(\text{Al}\) exhibits the same relative peak intensity as the \(3s\) peak for \(\text{Mg}\), indicating that both elements contain two valence electrons in their respective \(3s\) subshells.
- **C.** The observation that the \(1s\) peak for \(\text{Al}\) appears at a lower binding energy than the \(1s\) peak for \(\text{Mg}\), indicating that the core electrons in \(\text{Al}\) experience a smaller effective nuclear charge than those in \(\text{Mg}\).
- **D.** The observation that the \(3p\) peak for \(\text{Al}\) exhibits half the relative peak intensity of the \(3s\) peak in \(\text{Al}\), indicating that the \(3p\) subshell experiences increased electron-electron repulsion within the valence shell.

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