The Bond Order of CO Molecule is

The Bond Order of the CO molecule is equal to 3. Bond order is calculated by dividing the difference between the number of electrons in bonding orbitals and the number of electrons in anti-bonding orbitals by 2. In this article, we explain what the bond order of CO molecule is and how it is calculated.

The bond order of CO molecule is

What the bond order of CO molecule is?

The bond order of CO molecule, as mentioned above, is 3. The valence shell of carbon and oxygen has a total of 10 electrons. Instead of the conventional double bond seen in organic carbonyl compounds, the two atoms of carbon and oxygen, which both adhere to the octet rule, form a triple bond with six shared electrons in three bonding molecular orbitals.

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What is Bond Order?

Now that you know that the Bond Order of CO molecule is equal to 3, we, in this section, explain what bond order is.

Bond order is the difference between the number of electrons in bonding orbitals and the number of electrons in anti-bonding orbitals divided by 2. It is also equal to the difference between the number of bonds and anti-bonds in a molecule. Bond order can also be defined as the number of covalent bonds (electron pairs) between two atoms. Its formula is as follows.

\[Bond\ Order(B.O.) = {{electrons\ in\ bonding\ orbital – electrons\ in\ antibonding\ orbital} \over 2}\].
\[Bond\ Order \ (B.O.) = {{N_b-N_a} \over 2}\].

The above definition and formula were given by Linus Pauling, an American chemist, biochemist, peace activist, and author. The above formula is according to the Molecular Orbital Theory. However, the Molecular Orbital Theory is not the only theory describing the electronic structure of molecules.

For planar molecules with delocalized bonding, the Hückel molecular orbital theory provides a different method for establishing π bond ordering based on molecular orbital coefficients. As per the theory, bonding is divided into a sigma framework and a pi system. Charles Coulson used the orbital coefficients of the Hückel MOs to define the π-bond order between atoms r and s derived from Hückel theory. 

Bond order may not always be an integer in molecules that have resonance or nonclassical bonding. Generally speaking, the value of the bond order is directly proportional to the strength of the bond. 

For a very long time, there has been discussion about the notion of bond order in quantum mechanics. In 2017, a thorough method to determine bond order from quantum chemistry simulations was released.

How the bond order of CO molecule is calculated?

The bond order of CO molecule is calculated in the following way:

The molecular orbital electronic configuration of CO is: 

σ1s2σ*1s2σ2s2σ*2s2 π2Px2 = π2py2 σ2Py2

As can be seen above,

Electrons in Anti-Bonding Molecular Orbital = 4

Electrons in Bonding Molecular Orbital = 10

On applying the formula,

\[Bond\ Order \ (B.O.) = {{N_b-N_a} \over 2}\].
\[ = {{10-4} \over 2}\].
\[ = {{6} \over 2}\].
\[ = {3}\].

Hence proved that the Bond Order of CO molecule is 3

CO bond facts

  1. The Bond Order of CO molecule is equal to 3
  2. A triple bond that has a net of two pi bonds and one sigma bond connects the elements carbon and oxygen.
  3. The distance separating the carbon and oxygen atoms is 112.8 pm.
  4. As in molecular nitrogen (N2), which has a comparable bond length (109.76 pm) and roughly the same molecular mass, this bond length is compatible with a triple bond.
  5. The computed fractional bond order of carbon monoxide is 2.6, showing that the “third” bond is significant but only makes up a portion of the total bond.
  6. In terms of valence bonds, -CO+ is the most significant structure, followed by –C≡O+, which is not an octet but still contributes significantly to resonance because each atom has a neutral formal charge.
  7. Carbon monoxide is sometimes regarded as an incredibly stable carbene due to the lone pair and di-valence of carbon in this resonance structure.
  8. The three bonds in the CO molecule are strongly polarised polar covalent bonds.
  9. For the σ-bond, the polarisation toward the oxygen atom is 71% but for both π-bonds, it is 77%.
  10. The oxidation state of carbon in CO is +2

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