HOMO/LUMO facts for kids

HOMO stands for highest occupied molecular orbital. LUMO stands for lowest unoccupied molecular orbital. The energy difference between the HOMO and LUMO is called the HOMO-LUMO gap. HOMO and LUMO are sometimes known as frontier orbitals. These terms help scientists understand how molecules behave.

Every tiny space where electrons can be, called a molecular orbital (MO), has a specific energy level. Scientists arrange these orbitals from lowest energy to highest energy. Electrons always try to fill up the lowest energy spaces first, like filling a building from the bottom floor up.

For example, imagine a molecule has enough electrons to fill 15 orbitals. The 15th orbital that gets filled is the HOMO. It's the "highest" orbital that has electrons in it. The very next orbital, the 16th one, which is empty, is the LUMO. It's the "lowest" orbital that doesn't have any electrons yet.

Understanding the Energy Gap

The energy difference between the HOMO and LUMO is called the "HOMO-LUMO gap" or "band gap." This gap is super important! A smaller gap means it's easier for an electron to jump from the HOMO to the LUMO.

When an electron jumps from the HOMO to the LUMO, the molecule becomes "excited." This excitement can make a molecule do interesting things, like give off light. For example, knowing the size of this gap can help scientists predict if a substance will have luminescence, which is when something glows.

Related Discoveries

• Diels–Alder reaction
• Electron configuration
• Ligand
• Organic semiconductor

Images for kids

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  3D model of the highest occupied molecular orbital in CO2

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  3D model of the lowest unoccupied molecular orbital in CO2