Early atomic models made conflicting predictions about the relative energies of the…
CHEMISTRY · Multi-part · AP · Chemistry · Atomic Structure and Properties · Atomic Structure and Properties
Problem
Early atomic models made conflicting predictions about the relative energies of the 2s and 2p subshells in sodium. Model X asserted that 2p should be lower in energy than 2s, whereas Model Y predicted the opposite ordering. A modern PES experiment on sodium gives the following data (all values in kJ mol⁻¹):
• Peak P: 107 (relative height 2)
• Peak Q: 64 (relative height 6)
Respond to the prompts below.
(a) State each model’s prediction for the ordering of the 2s and 2p subshell energies and briefly describe the theoretical rationale offered by each model.
(b) Using the PES data, identify which model is supported experimentally. Cite specific features of the spectrum that lead to your conclusion.
(c) Provide a detailed explanation, rooted in penetration and shielding arguments, for why the experimentally observed ordering occurs.
(d) Sodium is the first element in Period 3. Discuss how the same PES evidence undermines the model that is not supported, particularly when the trend is followed across the rest of the period.