Highest occupied molecular orbital

Definition

The highest occupied molecular orbital (HOMO) is the molecular orbital that contains the highest energy electrons in a molecule and is fully or partially filled. It plays a crucial role in determining the reactivity and properties of molecules, as electrons in the HOMO are the most accessible for chemical bonding and interactions.

5 Must Know Facts For Your Next Test

1. The HOMO is crucial for predicting how a molecule will react with other molecules, as it often determines the sites of chemical reactivity.
2. In transition states during chemical reactions, electrons can be transferred from the HOMO of one molecule to the LUMO of another, which is essential for understanding reaction mechanisms.
3. The energy level of the HOMO can be affected by factors such as electronegativity, resonance structures, and steric effects, influencing molecular stability.
4. In spectroscopy, transitions involving electrons moving from the HOMO to higher energy states can provide insights into the electronic structure and properties of molecules.
5. Calculating the HOMO energy level helps chemists design molecules for specific applications, including drug design and materials science.

Review Questions

• How does the highest occupied molecular orbital influence a molecule's reactivity?
  • The highest occupied molecular orbital (HOMO) contains the most energetic electrons that are involved in chemical bonding. Because these electrons are more accessible for interactions with other molecules, the energy level and configuration of the HOMO can significantly influence how a molecule reacts with different species. If the HOMO is at a high energy level, it may lead to increased reactivity and a greater likelihood of forming new bonds.
• Compare and contrast the roles of HOMO and LUMO in chemical reactions.
  • The highest occupied molecular orbital (HOMO) contains the electrons available for bonding, while the lowest unoccupied molecular orbital (LUMO) is where electrons can be promoted during interactions. During chemical reactions, electron transfer typically occurs from the HOMO of one reactant to the LUMO of another. This transfer is fundamental in understanding reaction mechanisms, as it highlights how changes in electronic structure can lead to various outcomes in chemical reactivity.
• Evaluate how molecular orbital theory enhances our understanding of molecular stability and reactivity through concepts like HOMO.
  • Molecular orbital theory provides a framework for analyzing the behavior of electrons within molecules by focusing on orbitals that encompass multiple nuclei. The concept of the highest occupied molecular orbital (HOMO) allows chemists to assess how electron distribution affects stability and reactivity. By understanding how factors such as electronegativity or resonance impact the energy level of the HOMO, researchers can better predict which molecules are likely to react under specific conditions, thus contributing to advancements in fields like organic synthesis and materials science.

Related terms

Lowest Unoccupied Molecular Orbital:

The lowest unoccupied molecular orbital (LUMO) is the molecular orbital that is empty and has the lowest energy among all unoccupied orbitals, which is important in understanding electron transitions and reactivity.

Molecular Orbital Theory: Molecular orbital theory describes the behavior of electrons in a molecule using quantum mechanics, where atomic orbitals combine to form molecular orbitals that can be occupied by electrons.

Valence Electrons: Valence electrons are the outermost electrons of an atom that are involved in forming bonds with other atoms, influencing molecular structure and reactivity.