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Why do electrons in a bonding molecular orbital stabilize a molecule?
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covalent bond
In polar covalent bonds, such as that between hydrogen and oxygen atoms, the electrons are not transferred from one atom to the other as they are in an ionic bond. Instead, some outer electrons merely spend more time in the vicinity of the other atom. The effect of this orbital distortion is to induce regional net charges that hold the atoms together, such as in water molecules.
In molecular orbital theory, electrons in a bonding molecular orbital stabilize a molecule because they occupy a state of lower energy compared to their energy level when confined to individual atomic orbitals.12
This stabilization occurs through the following mechanism:
- Constructive Interference: When atomic orbitals combine to form a bonding molecular orbital, their wave functions interfere constructively. This results in an enhanced amplitude of the electron wave function in the internuclear regionāthe space between the two nuclei.2
- Increased Electron Density: Because of this constructive interference, there is a high probability of finding the electrons between the nuclei. This accumulation of electron density in the internuclear region effectively shields the nuclei from one another's repulsion and provides an attractive force that holds the atoms together.2
- Energetic Favorability: The system transitions from a state of higher energy (separated atoms) to a state of lower energy (the bonded molecule). Because the bonding orbital is at a lower energy level than the constituent atomic orbitals, the formation of the bond is energetically favored.12