molecular orbital theory

Atoms in antibonding orbitals have higher energies

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atoms in antibonding orbitals have higher energies than if they were alone In general when two atomic orbitals are added together to form molecular orbitals, one of the resultant molecular orbitals will be lower in energy (bonding orbital) than the other atomic orbitals that will be higher in energy (antibonding orbital) bonding orbitals result from the addition of two atomic orbitals in phase while antibonding orbitals result from the subtraction of orbital that are out of phase and cancel each other out the bonding orbital has increased electron density in the internuclear region while the antibonding orbital has a node in the internuclear region bonding orbitals have greater electron density in their internuclear region and therefore lower their energy compared to orbitals in non bonded atoms two hydrogen atoms can lower their overall energy by forming H2 because the electrons can move from higher energy atomic orbitals into the lower energy sigma 1s bonding molecular orbital. bond order = (number of electrons in bonding molecular orbitals - number of electrons in antibonding molecular orbitals) / 2 a positive bond order means that there are more electrons in bonding molecular orbitals than in antibonding molecular orbitals and therefore the electrons will have a lower energy than they did when they were in the orbitals of the isolated atoms the greater the bond order, the stronger the bond a negative or zero bond order generally means that a bond will not form between the atoms e.g. He2
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the bond order is (2-2)/2 = 0 and therefore there is not net stabilization by joining two
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