Molecular orbitals of three or more atoms

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Discussion Overview

The discussion centers on the molecular orbitals formed by three or more atoms within the framework of molecular orbital theory. Participants explore the characteristics of these molecular orbitals, including bonding and anti-bonding properties, as well as the complexity introduced by additional atoms.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant describes how two atomic orbitals combine to form bonding and anti-bonding molecular orbitals, extending this concept to three atoms and questioning the nature of the resulting orbitals.
  • Another participant notes that the model becomes more complex as more atoms are added, referencing a resource on linear triatomic molecules.
  • A further contribution outlines the specific coefficients and characteristics of the molecular orbitals formed by three equal s orbitals, identifying one as bonding, one as non-bonding, and one as anti-bonding, along with their respective nodes.
  • A request for an elementary reference on molecular orbitals that avoids group theory is made, indicating a desire for more accessible material.
  • Another participant suggests looking for "qualitative molecular orbital theory" as a potential resource, but does not provide specific titles.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and complexity regarding molecular orbitals of three or more atoms. There is no consensus on a definitive model or reference material, and the discussion remains open-ended with multiple viewpoints presented.

Contextual Notes

The discussion reflects limitations in the complexity of molecular orbital theory as more atoms are considered, and the need for accessible resources that do not rely on advanced concepts like group theory.

hokhani
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In Molecular orbital theory, when two atoms A & B come close to each other, their atomic orbitals (say their s orbitals) combine and make two molecular orbitals, one bonding and the other anti-bonding. How about molecular orbitals of three or more atoms? For three atoms say A & B & C we would have three molecular orbitals obtained from their s atomic orbitals. Which of them are bonding and which anti-bonding?
 
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For three equal s orbitals in a line with equal distance, there will be three molecular orbitals with coefficients of the atomic orbitals A, B and C equal to (up to overall normalization) (a,b,a), (1,0,-1), and (c,-d,c), where a, b, and c are positive numbers. The first one is bonding (positive overlap between all orbitals), the second one non-bonding (as there is no overlap between neighbouring atoms) and the third one anti-bonding (negative overlap). The first one has no nodes, the second one one node (change from plus to minus) and the third one two nodes. Correspondingly, for four atoms you get one with no nodes, one with one node, one with two nodes and one with three nodes which are consecutively higher in energy.
 
Thanks. Could You please introduce me an elementary reference that deals with molecular orbitals without using group theory?
 
Last edited:
Look out for "qualitative molecular orbital theory". I can't help you with specific titles.
 
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