The photoelectron spectrum (PES) of gaseous magnesium at a particular photon energy…
CHEMISTRY · Multi-part · AP · Chemistry · Atomic Structure and Properties · Atomic Structure and Properties
Problem
The photoelectron spectrum (PES) of gaseous magnesium at a particular photon energy is described below.
• Binding-energy peaks (in kJ mol⁻¹): 1250 (peak height 2), 90 (2), 65 (6), 9 (2)
• The horizontal axis is binding energy increasing to the left; peak heights are proportional to the number of electrons removed from each subshell.
Answer the following questions about the spectrum and what it reveals about magnesium’s electronic structure.
(a) Identify which of the four listed peaks correspond to core electrons and which correspond to valence electrons. Justify your classification in terms of relative binding energies.
(b) Both the 90 kJ mol⁻¹ peak and the 65 kJ mol⁻¹ peak originate from electrons in the n = 2 shell. Explain why the 2s electrons give rise to the peak at the higher binding energy even though 2s and 2p have the same principal quantum number.
(c) The two lowest-energy peaks have relative heights of 6 : 2. Connect these relative intensities to the ground-state electron configuration of magnesium, and explain how the spectrum provides experimental support for that configuration.