H3 Chemistry 9813 · Study focus: H3 Chemistry: Explain discrete molecular-orbital energy levels
H3 Chemistry: Explain discrete molecular-orbital energy levels
Start from the governing chemical model, test it against evidence, then transfer the reasoning to an unfamiliar case.
Your success criteria
- Explain discrete molecular-orbital energy levels
- Use named chemical evidence.
- Transfer the governing reason to an unfamiliar case.
Orientation and prerequisite retrieval
A molecular orbital corresponds to an allowed discrete electronic energy level.
An electron cannot occupy an arbitrary stationary energy between two MO levels.
Definitions and exact language
A transition requires an energy change equal to the difference between allowed levels.
The horizontal position of a drawn MO level has no energy meaning; vertical position does.
Pauli exclusion limits one orbital to two electrons of opposite spin.
Degenerate orbitals have equal energy even when drawn as separate lines.
Text alternative: Text alternative: Hund's rule places electrons singly in degenerate orbitals before pairing. A valid diagram labels energy direction and distinguishes levels from electron arrows.
Detailed molecular explanation
Pauli exclusion limits one orbital to two electrons of opposite spin.
Degenerate orbitals have equal energy even when drawn as separate lines.
Worked leaf-specific case
Hund's rule places electrons singly in degenerate orbitals before pairing.
An empty allowed level remains a molecular orbital and can be a LUMO.
- A candidate writes, “A molecular orbital is the path through every intermediate energy.” Which correction should replace it?
Open the feedback checkpoint after attempting
- A molecular orbital corresponds to an allowed discrete electronic energy level.
Guided evidence check
A continuous absorption band does not imply that a molecule has continuous electronic energies.
Thermal motion can broaden spectral features without removing underlying quantisation.
- Which labelled diagram, spectrum or calculation would most directly disprove “Horizontal spacing between MO lines shows the energy gap.”?
Open the feedback checkpoint after attempting
- The horizontal position of a drawn MO level has no energy meaning; vertical position does.
Independent transfer
Energy-zero choice may shift every plotted level without changing level gaps.
A valid diagram labels energy direction and distinguishes levels from electron arrows.
- Design a specific chemical check that would expose the error in “Electrons pair in one degenerate orbital before another is occupied.”
Open the feedback checkpoint after attempting
- Hund's rule places electrons singly in degenerate orbitals before pairing.
Misconception repair
Misconception: Changing the diagram's energy zero changes transition energies.
Repair: Energy-zero choice may shift every plotted level without changing level gaps.
- Write leaf-specific feedback for the misconception “Changing the diagram's energy zero changes transition energies.”
Open the feedback checkpoint after attempting
- Energy-zero choice may shift every plotted level without changing level gaps.
Practice, unseen assessment, re-test and next step
Complete the diagnostic questions, review the feedback, then attempt the final check.
After delayed re-test, continue to Apply LCAO to homonuclear diatomic molecules at /learning/h3-molecular-orbitals-lcao-diatomics-lesson.html.
- Review the feedback for each diagnostic question, then attempt the final check.
Open the feedback checkpoint after attempting
- Before moving on, state this boundary: A valid diagram labels energy direction and distinguishes levels from electron arrows.