NO Bond Order | MO Diagram of NO, NO+

Before we find the NO bond order, I have a question what do you know about NO? NO is the nitric oxide. Nitric oxide contains a single unpaired electron. It is free radical and therefore it is very reactive. It is a neutral and colorless gas. In the laboratory, it can be prepared by the reduction of dilute HNO3 with copper. The reaction involved is 3 moles of Cu reacting with 8 moles of nitric acid to give the product:

3Cu + 8HNO3 → 2NO + 3Cu(NO3)2 + 4H2O

It can also be prepared by the reduction of HNO2 with an iodide ion.

2HNO2 + 2I + 2H → 2NO + I2 + 2H2O

NO Bond Order Explain with Structure

Now let us look at the structure of nitric acid.

NO structure

This is the space fill model of nitric oxide. The bond length of NO is 115 pm which is intermediate between a double bond and a triple bond. The NO bond order is 2.5. The NO bonding is well explained by using molecular orbital theory. The bonding is similar to that in nitrogen molecule and carbon monoxide which both have 10 valence electrons. NO has 11 valence electrons and the extra unpaired electron occupies an antibonding π*2p orbital. This extra electron reduces the bond order from 3 to 2.5.

Molecular Orbital of NO

NO bond order

NO Bond Order By using Formula

The formula to calculate the bond order of NO is the number of electrons in the bonding orbital minus the number of electrons in the antibonding orbital divided by 2.

Bond order = no. of an electron in bonding – no. of an electron in antibonding / 2

Bond order = 8 – 3 / 2

Bond order = 5 / 2

Bond order = 2.5

Is NO Paramagnetic or Diamagnetic?

Do you know

  • If electrons are paired then diamagnetic
  • If electrons are unpaired then paramagnetic

NO has one unpaired electron in π*2p orbital so it is paramagnetic in nature.

Molecular Orbital of NO+

Now, look carefully at the molecular orbital diagram of NO, the last electron is in the π*2p orbital since this last electron is in an antibonding orbital, the bond order is reduced to 2.5. Now let’s suppose this last electron in the π*2p orbital is removed then the molecular orbital diagram is given below:

Molecular Orbital of NO+

NO+ Bond Order

NO+ bond order is similar to nitrogen which is 3.

Bond order = no. of an electron in bonding – no. of an electron in antibonding / 2

Bond order = 8 – 2 / 2

Bond order = 6 / 2

Bond order = 3

Is NO+ Paramagnetic or Diamagnetic?

NO+ has no unpaired electron so it is diamagnetic in nature.

Which is more Stable NO or NO+?

The stability of molecules depends upon the bond order. The greater the bond order, the greater will be the stability.

  • The NO bond order is 2.5
  • The NO+ bond order is 3

The NO+ is more stable than NO.

Properties of Nitric Oxide

The molecules having odd electrons are usually highly reactive and tend to dimerize. Nitric oxide is unusually stable for an odd electron molecule. When nitric oxide is reacted with oxygen to give NO2.

2NO + O2 → 2NO2

When nitric oxide is reacted with halogens it gives nitrosyl halides such as NOCl.

2NO + Cl2 → 2NOCl

The NO gas is paramagnetic because it contains an unpaired electron. However, it is daimegnatic in solid and liquid state because the molecule diamerize, forming O-N-N-O. Nitric oxide also forms coordination complexes with d-block elements. These complexes called nitrosyls. NO and Fe2+ form the coordination complex [Fe(H2O)3NO]2-, which is responsible for the colour in brown-ring test for nitrates. NO acts as the three electron donor and ligands which donates two elecrons. Thus three carbon monoxide groups may be replaced by two NO groups.

[Fe(CO)5] + 2NO → [Fe(CO)2(NO)2] + 3CO

[Cr(CO)6] + 4NO → [Cr(NO)4] + 6CO

Uses of Nitric Oxide

Nitric oxide is an important intermediate in the manufacturing of nitric acid HNO3 by the catalytic oxidation of ammonia (Ostwald process).

Related Blog

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