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How do molecular orbitals explain why covalent bonds form?
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chemical compound
Methane, in which four hydrogen atoms are bound to a single carbon atom, is an example of a basic chemical compound. The structures of chemical compounds are influenced by complex factors, such as bond angles and bond length.
According to molecular-orbital theory, covalent bonds form because the resulting system achieves a lower energy state than the isolated atoms. When atoms approach, their atomic orbitals combine to form molecular orbitals that are distributed over the entire molecule.12
This process occurs through the superposition of atomic orbitals, which can interfere in two ways:
- Constructive interference: The amplitudes of atomic orbitals add together, creating a bonding orbital with enhanced electron density between the nuclei. This orbital exists at a lower energy level than the original atomic orbitals.31
- Destructive interference: The amplitudes are subtracted, creating an antibonding orbital with a nodal plane of zero electron density between the nuclei. This orbital exists at a higher energy level.13
A covalent bond forms when valence electrons occupy the lower-energy bonding orbital. Because the system moves from a state of higher energy to one of lower energy, the formation of the bond is energetically favored.13