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1.6Atomic Structure and Properties

Photoelectron Spectroscopy — AP CHEMISTRY Revision Notes & Topical Questions

5 min read 9 parts Lesson 14 of 16 1 quiz

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Lesson summary

1.6 Photoelectron Spectroscopy — Notes — AP CHEMISTRY notes: Interpret photoelectron spectra to deduce electron configurations and support the shell model.Photoelectron spectroscopy uses high-energy radiation to eject electrons from atoms.Measuring the kinetic energy of the eject…

  • Energy conservation
  • Binding energy
  • Peak position
  • Peak height
  • Core electrons
  • Each peak corresponds to one subshell (1s, 2s, 2p ...)

Section 1 of 9Principle of PES

Photoelectron spectroscopy uses high-energy radiation to eject electrons from atoms.
Measuring the kinetic energy of the ejected electrons gives their binding energy.
Energy conservation
  • Energy conservation binding energy = photon energy − kinetic energy (Ebinding = hν − KE).
Binding energy
Binding energy the energy needed to remove an electron against the nuclear attraction.

Section 2 of 9Reading a spectrum

1
The x-axis is binding energy and the y-axis is the relative number of electrons.
2
Each peak corresponds to one subshell (1s, 2s, 2p ...).
3
Peak position shows the energy to remove electrons from that subshell.
  • Higher binding energy means electrons closer to the nucleus and less shielded.
  • The 1s peak is always at the highest binding energy.
4
Peak height is proportional to the number of electrons in the subshell, so 2p6 is three times as tall as 2s2.

Section 3 of 9Identifying an element

1
Identify the highest-energy peak as 1s.
2
Assign the next peaks in order: 2s, 2p, 3s, 3p, 4s, 3d.
3
Use the relative heights to find electrons in each subshell.
4
Add the electrons to get Z and name the element.
5
Explain peak positions with nuclear charge, distance and shielding.

Section 4 of 9Comparing elements

The same subshell has a higher binding energy in an element with larger Z because of greater nuclear charge.
Example
  • Example the 1s binding energy of Na is greater than that of Ne.
The lowest-binding-energy peak corresponds to the valence electrons and relates to the first ionisation energy.

Section 5 of 9Evidence for the shell model

Evidence for the shell model
Large gaps in binding energy separate shells.
Smaller gaps separate subshells within the same shell.
Core electrons have high binding energy and valence electrons have low binding energy.

Section 6 of 9Sodium spectrum

PeakSubshellElectrons (relative height)Binding energy
11s2Highest
22s2High
32p6Medium
43s1Lowest

Section 7 of 9More from the specification

More from the specification
Periodic
  • Describing properties that repeat at regular intervals along the table
Aufbau principle
  • Fill the lowest energy subshells first.
Outer shell
  • Highest-energy occupied shell.
Proton
  • Positive particle in the nucleus.
Orbital
  • A region of space around the nucleus that holds up to two electrons of opposite spin.
Neutron
  • Neutral particle in the nucleus.
Coulomb
  • The unit of charge; one ampere for one second.
Particle
  • A tiny portion of matter, too small to see.

Section 8 of 9Key terms

TermMeaning
Photoelectron spectroscopyTechnique measuring the energies of electrons ejected by radiation.
Binding energyEnergy needed to remove an electron from an atom.
Peak positionShows the binding energy of a subshell.
Peak heightProportional to the number of electrons in the subshell.
Core electronsInner electrons with high binding energy.
ShieldingReduction of nuclear attraction on outer electrons by inner electrons.

Section 9 of 9Exam technique

1
Reading peak height as energy — height shows the number of electrons
2
Assigning the 1s peak to the lowest binding energy — it has the highest
3
Forgetting that PES energies depend on nuclear charge — the same subshell has higher binding energy for larger Z
4
Mixing up valence and core electrons — valence electrons have the lowest binding energy

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