Why NO and CN- Have the Same Bond Order and Magnetism

In the study of molecular structures, the bond order and magnetic properties of molecules can provide valuable insights into their electronic configurations. Interestingly, the molecules NO (nitric oxide) and CN- (cyanide ion) exhibit identical bond orders and magnetic properties. This article aims to elucidate the underlying reasons for these similarities through molecular orbital theory.

Valence Electron Count and Bond Order

The bond order of a molecule is determined by the number of bonding electron pairs between the atoms. The formula to calculate bond order is:

Bond Order (Number of Bonding Electrons - Number of Antibonding Electrons) / 2

Let's begin by analyzing the valence electrons in both NO and CN-.

NO (Nitric Oxide)

NO contains a nitrogen atom and an oxygen atom. Nitrogen has 5 valence electrons, and oxygen has 6. Thus, the total number of valence electrons is:

5 (from N) 6 (from O) 11 valence electrons

However, NO is a cation, meaning it has lost one electron, resulting in:

10 valence electrons

CN- (Cyanide Ion)

For CN-, the carbon atom has 4 valence electrons, and the nitrogen atom has 5. Therefore, the total number of valence electrons is:

4 (from C) 5 (from N) 9 valence electrons

However, since CN- is an anion, it has gained one electron, resulting in:

10 valence electrons

Applications of Molecular Orbital Theory

To understand the bond order and magnetic properties of these molecules, we can employ molecular orbital theory. Molecular orbital theory describes the distribution of electrons in the molecular orbitals formed by the overlap of atomic orbitals.

Electron Distribution in NO

In NO, the 10 valence electrons will occupy the bonding orbitals. The molecular orbitals formed include sigma (σ) and pi (π) orbitals. Typically, the bonding orbitals will be the lowest in energy, followed by the antibonding orbitals. This distribution results in a bond order of 3, which corresponds to a triple bond.

Electron Distribution in CN-

Similarly, in CN-, the 10 valence electrons will occupy the molecular orbitals. Again, the bond order is determined by the number of bonding electrons minus the antibonding electrons, divided by 2. The distribution will be such that the bond order is also 3.

Bond Order and Magnetic Properties

Both NO and CN- exhibit the same bond order of 3, which means they both have a triple bond. The magnetic properties of these molecules are also the same due to their identical electron configurations.

Magnetic Properties

Both NO and CN- are diamagnetic, meaning they have no unpaired electrons. This is because the 10 valence electrons in each molecule are all paired in the molecular orbitals. Since diamagnetic species do not have a net magnetic moment, they are not attracted to magnetic fields.

Summary and Conclusion

In summary, the identical electron configurations of NO and CN- result in the same bond order and magnetic properties. Specifically, both molecules have a bond order of 3 and are diamagnetic, indicating that they have no unpaired electrons.

The application of molecular orbital theory helps us understand these phenomena in detail. By analyzing the distribution of electrons in the molecular orbitals, we can accurately determine the bond order and magnetic properties of these molecules.

This article has demonstrated that molecular orbital theory provides a powerful tool for understanding the electronic structure and properties of molecules, making it an essential concept in the field of chemistry.