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Photoelectron Spectroscopy

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Photoelectron spectroscopy measures the energy needed to eject electrons from each subshell of an atom. The result is a spectrum whose peak positions give binding energies (how tightly a subshell is held) and whose peak heights give the number of electrons in that subshell. Read together, the two axes reconstruct the electron configuration from experimental data.

UNIT 1 TOPIC 1.6 • PHOTOELECTRON SPECTROSCOPY PES BUILDER 1. Element: Phosphorus, Z = 15 2. Configuration: 1s² 2s² 2p⁶ 3s² 3p³ PES SPECTRUM NUMBER OF ELECTRONS 1s 2 e⁻ 189 MJ/mol 189 2s 2 e⁻ 18.7 MJ/mol 18.7 2p 6 e⁻ 13.5 MJ/mol 13.5 3s 2 e⁻ 1.95 MJ/mol 1.95 3p 3 e⁻ 1.06 MJ/mol 1.06 BINDING ENERGY (MJ/mol) (compressed scale — not to scale) Binding energy decreases left → right. Higher binding energy = held more tightly. EACH PEAK = a subshell PEAK HEIGHT = electrons in that subshell HIGHER BINDING ENERGY = held closer to the nucleus PES INFERS subshell structure + electron counts AP Chemistry · Unit 1 · Atomic Structure & Properties
A PES spectrum maps an atom's subshells. Each peak sits at the binding energy of a subshell (higher energy = closer to the nucleus, so 1s is far left) and its height counts the electrons in that subshell (2 for 1s, up to 6 for a full p). Position and height carry different information.
PES Builder · Open the sandbox →

Every trap here comes from crossing the two axes: treating a peak's height as its binding strength, reading the left-to-right peak order as the filling order, or labelling a subshell from how tall its peak is. Height counts electrons; position measures how tightly they are bound. They are independent.

The work

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Lesson
Photoelectron Spectroscopy ›

A PES spectrum encodes binding energy on one axis and electron count on the other, and students routinely fuse them. The lesson keeps the axes separate, then closes with a ten-scenario applet that builds spectra from configurations.

Skill check · 10 scenarios
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Diagnostic
10-item topic check ›

Ten items spanning the three Topic 1.6 misconceptions: reading peak height as binding strength, reading peak order as filling order, and naming a subshell by its peak height rather than its binding energy.

Not started · 10 items · ~15 min
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Targeted Practice
Drill a single misconception ›

Pick one of the failure modes you missed and drill it on its own. The round is adaptive: two correct in a row clears the misconception and moves you to the next.

Take the diagnostic to identify your misconceptions
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