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H 2 1sσ* antibonding molecular orbital. In theoretical chemistry, an antibonding orbital is a type of molecular orbital that weakens the chemical bond between two atoms and helps to raise the energy of the molecule relative to the separated atoms. Such an orbital has one or more nodes in the bonding region between the nuclei.
For example, N 2, with eight electrons in bonding orbitals and two electrons in antibonding orbitals, has a bond order of three, which constitutes a triple bond. Bond strength is proportional to bond order—a greater amount of bonding produces a more stable bond—and bond length is inversely proportional to it—a stronger bond is shorter.
The MO diagram for dihydrogen. In the classic example of the H 2 MO, the two separate H atoms have identical atomic orbitals. When creating the molecule dihydrogen, the individual valence orbitals, 1s, either: merge in phase to get bonding orbitals, where the electron density is in between the nuclei of the atoms; or, merge out of phase to get antibonding orbitals, where the electron density ...
Molecular orbital diagram of He 2. Bond order is the number of chemical bonds between a pair of atoms. The bond order of a molecule can be calculated by subtracting the number of electrons in anti-bonding orbitals from the number of bonding orbitals, and the resulting number is then divided by two. A molecule is expected to be stable if it has ...
The resulting electron configuration can be described in terms of bond type, parity and occupancy for example dihydrogen 1σ g 2. Alternatively it can be written as a molecular term symbol e.g. 1 Σ g + for dihydrogen. Sometimes, the letter n is used to designate a non-bonding orbital. For a stable bond, the bond order defined as
The corresponding antibonding, or σ* orbital, is defined by the presence of one nodal plane between the two bonded atoms. Sigma bonds are the strongest type of covalent bonds due to the direct overlap of orbitals, and the electrons in these bonds are sometimes referred to as sigma electrons. [3] The symbol σ is the Greek letter sigma.
The orbital diagram breaks down as follows: The 18 framework molecular orbitals, (MOs), derived from the 18 boron atomic orbitals are: 1 bonding MO at the center of the cluster and 5 antibonding MOs from the 6 sp-radial hybrid orbitals; 6 bonding MOs and 6 antibonding MOs from the 12 tangential p-orbitals.
In molecular orbital theory, bond order is defined as half the difference between the number of bonding electrons and the number of antibonding electrons as per the equation below. [4][5] This often but not always yields similar results for bonds near their equilibrium lengths, but it does not work for stretched bonds. [6] Bond order is also an ...