Chemistry Figures Photoelectron Spectrum
1,000100101012345678Binding energy (MJ/mol)Relative number of electrons

Photoelectron spectra (PES) for AP Chemistry

Photoelectron Spectrum draws the photoelectron spectrum of any neutral atom from hydrogen to xenon: one peak for each sublevel of its ground-state electron configuration, as tall as that sublevel’s electrons, at its binding energy. Binding energy falls from left to right, as AP Chemistry draws it, in MJ/mol or eV. Exceptions like chromium and copper are drawn with their real configurations.

Core electrons are held a thousand times more tightly than valence electrons, so the energy axis is logarithmic, or broken into a stretch for each group of peaks, or linear if you want the crowding to show. Label peaks with their sublevels, electron counts and energies, or leave the labels blank; hide the element for “which element is this?”, and draw a second element dashed behind the first to ask why its peaks have moved.

What you can set

  • The element, hydrogen to xenon, and a second element to compare, drawn dashed behind it
  • Binding energy in MJ/mol or eV, on a logarithmic, broken or linear axis
  • Peaks drawn as smooth peaks or as bars
  • Sublevel labels written, as blank lines, or left off, with electron counts and binding energies over the peaks
  • A numbered electrons axis and gridlines, element names shown or hidden, and the label size
  • A chart title, and an answer key line with each element’s electron configuration

Copying, printing and sharing

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Example figures

Frequently asked questions

How do you read a photoelectron spectrum?

Each peak is one sublevel. Its height is the number of electrons in that sublevel, and its position is how much energy it takes to remove one of them. The peak furthest left is 1s; the one furthest right holds the valence electrons.

Why is binding energy higher on the left?

That’s how AP Chemistry and most textbooks draw photoelectron spectra, with the axis running from high energy to low. The generator follows it, so its figures match what students see on the exam.

Why do one element’s peaks sit to the left of another’s?

An element with more protons pulls its electrons more tightly, so its core peaks are always at a higher binding energy, further left. Compare magnesium with sodium to show it. A valence peak can go the other way: oxygen’s 2p peak sits just right of nitrogen’s, because oxygen’s fourth 2p electron shares an orbital and is pushed away by its partner.

Why is the axis logarithmic or broken?

A 1s electron can be held thousands of times more tightly than a valence electron (calcium’s 1s is about 390 MJ/mol, its 4s about 0.6), so on an even axis the valence peaks crowd together at the right. A logarithmic or broken axis keeps every peak readable.

Where do the binding energies come from?

Hydrogen to calcium use the textbook table AP materials quote (neon: 84.0, 4.68 and 2.08 MJ/mol). Scandium to xenon use Lotz’s 1970 table of electron binding energies in free atoms, converted from eV.

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