Structure and Bonding: The Oxides of Nitrogen

Can a compound have half a covalent bond or a bond order of 0.5?  Explain.

Let's examine the molecular structures of some oxides of nitrogen.  The oxides of nitrogen, NO and NO2, are notorious as air pollutants from combustion sources, such as cars and electric power plants.  Another common oxide is N2O known as laughing gas.  Draw or look up the Lewis dot structures for these oxides of nitrogen.

Here are the typical bond lengths for single, double, and triple nitrogen-to-nitrogen bonds.

single bond double bond triple bond
147 pm 124 pm 110 pm

Which bond order is the strongest?  Why?

Here are the typical bond lengths for single and double nitrogen-to-oxygen bonds.  A triple nitrogen-to-oxygen bond is not possible in a neutral oxide of nitrogen.

single bond

double bond
 140 pm 121 pm

Examine the structure of NO shown below.  Measure and record the bond distances (right click, select mouse click action, then click on distance).  How would you characterize the bond in this simple molecule?

Look at the structure of N2O and describe the N-N bond and the N-O bond in the molecule.

Both NO and N2O have unusual bond orders.  NO has a bond order of 2.5, while in N2O the N-N bond is 2.5 and the N-O is 1.5.

Now examine the structures of NO2 and N2O4 as given below.  The formation of N2O4 occurs by the dimerization of NO2

2 NO2(g)  =  N2O4(g)

Does every collision between two NO2 molecules result in dimerization?  Explain.

Sketch how the two molecules of NO2 must collide?  

Measure the bond angle in NO2.  Right click on each image and go to select, then to mouse click action, and click on angle.  Why is this angle not 120o or less?

From the Lewis dot structure of NO2 you may have a structure with both a single and double N-O bond.  Measure the bond length in NO2 and decide if your structure in correct.

Both of the N-O bonds in NO2 have a bond order of 1.5.  A resonance structure exists where both N-O bonds are the same length, intermediate in length between a single and double bond.  The large bond angle is due to a lone electron (single electron not a lone pair) in the ideal trigonal planar geometry

How would you characterize the strength of the N-N bond in N2O4?

  

The N-N bond in N2O4 would be weak compared to a typical single bond due to its long bond length.

The nitrogen-oxygen bond distance in NO+ is 106 pm.  Estimate the bond order in this ion.  Explain your method.

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