Dinitrogen Pentoxide

Dinitrogen pentoxide is a chemical compound containing only nitrogen and oxygen. As the name suggests, a single molecule of Dinitrogen Pentoxide will have 2 (di) nitrogen atoms and 5 (Pent) oxygen atoms. The chemical formula of the compound is N₂O₅. 

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Dinitrogen pentoxide is the anhydride form of nitric acid that can exist as a colourless crystal. It melts at 30°C. A rather unstable oxide of nitrogen, dinitrogen pentoxide is used as an oxidiser in a number of chemical reactions. It is a nitrating agent. Nowadays, however, it is being replaced largely by nitronium tetrafluoroborate. 

Chemical Structure: Lewis Structure of Dinitrogen Pentoxide (N₂O₅)

As mentioned above, Dinitrogen Pentoxide is composed of 2 Nitrogen atoms and 5 Oxygen atoms. Now, if you want to draw the Lewis Dot Structure of N₂O₅, you first have to know a few basic things:

• Nitrogen has 5 valence electrons

• Oxygen has 6 valence electrons

So, in N₂O₅, there will be: 

• 5*2 = 10 valence electrons of Nitrogen

• 6*5 = 30 valence electrons of Oxygen

Hence, we will be working with 40 valence electrons.

Now carefully go through the following facts:

• The total number of atoms in N₂O₅ is 2+5 = 7

• We know that each of these atoms must have 8 electrons in its valence shell. So there should be 7 * 8 = 56 valence electrons in the compound.

• So we have 40 electrons at hand. Deficit is 56 - 40 = 16 electrons. Since the compound has 2 atoms only - there will be a total of \[\frac {16}{2}\] = 8 bonds. 

So, now let us first arrange the atoms in the compound.

So the double bond completes the 8 bonds. You might ask - why can’t the two nitrogen atoms form double bonds with the oxygen in the middle? That would ultimately make the oxygen electropositive which is unnatural - Oxygen should be kept electro-negative as this is what we see in nature.

Now let us complete the octet and see what the Lewis dot diagram of N₂O₅ looks like:

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So the octet rule is fulfilled. The nitrogen atoms have a positive charge of +1 each. The charge of oxygen atoms is 0.

Properties of Dinitrogen Pentoxide 

The important properties of dinitrogen pentoxide are as follows:

• It is a colourless crystalline solid. However, you cannot keep it under room temperature (at least in India) because its melting point is 30°C.

• Upon being melted at 30°C, it transforms into a yellowish liquid.

• Be careful while handling N₂O₅. If you heat it beyond 30°C, it will get decomposed but the decomposition will take place along with the explosion. Upon heating, N₂O₅ will get dissociated into nitrogen dioxide (NO₂) and oxygen (O₂).

N₂O₅ is an Acidic Anhydride 

Anhydride is a compound that is formed after removing water molecules from a bigger compound. So anhydride basically means - without water. 

N₂O₅ is just HNO₃ without water. Since HNO₃ or Nitric acid is an acid, dinitrogen pentoxide is acid too. If HNO₃ can be dehydrated to obtain N₂O, we should be able to do the reverse as well. Here goes the reaction:

N₂O₅ + H₂O → 2HNO₃

So we can get nitric acid by adding water to dinitrogen pentoxide.

Preparation of N₂O₅ 

We can prepare dinitrogen pentoxide (N₂O₅) by dehydrating nitric acid with Phosphorus pentoxide. The reaction will look like this:

P₄O₁₀ + 12HNO₃ → 4H₃PO₄ + 6N₂O₅

Furthermore, since N₂O₅ is formed from HNO₃, the salt that N₂O₅ forms will also be the salt of HNO₃. The reaction will look like this:

N₂O₅ + NaOH → NaNO₃ + H₂O

We get sodium nitrate which is a salt of HNO₃.

The ionic form of N₂O₅:

The ionic form of Dinitrogen pentoxide is nitronium nitrate. This can be demonstrated with the help of the following reaction:

N₂O₅ + NaCl → NaNO₃ + NO₂Cl

The sodium atom has a +1 charge while the NO₃ atom has a -1 charge. Hence the ionic form of N₂O₅ is NaNO₃. However, you must also note that in NO₃ the Oxygen and Nitrogen have covalent bonds and we know that covalent bonds do not have ions. Interesting, isn’t it?

Decomposition of Dinitrogen Pentoxide 

When you are asked to find the rate of the decomposition of N₂O₅, the passage of time will be given, the initial concentration of the compound and the final concentration of the compound after the given time has elapsed will be given.  

The balanced formula looks like this:

2N₂O₅ → 4NO₂ + O₂

So suppose the passage of time is x. The initial concentration was y and the ultimate concentration is z, then the formula to know the average rate of decomposition will be:

-½(y−Z)molL⁻¹/x 

The actual formula looks like this: 

Rate of decomposition =  \[\frac {1}{2} \frac {-\Delta N_2O_5}{\Delta T} \]

Why \[\frac {1}{2}\]? Because we have written 2NO₂. Why a minus sign? Because the concentration is getting depleted.

If we are asked to find the rate of formation of NO₂, the formula would be:

 \[\frac {1}{4} {\frac {\Delta NO_2}{\Delta T}} \]

You will think why are we writing \[\frac {1}{4}\]? It is because we have written 4 NO₂. Why + \[\frac {1}{4}\] and not \[-\frac {1}{4}\]? It is because we are gaining NO₂. 

Uses of Dinitrogen Pentoxide 

Dinitrogen pentoxide was used as a nitrating agent. However, due to its unstable nature, these days Nitronium Tetrafluoroborate is being used instead of N₂O₅. A potential evil use of N₂O₅ is making TNT from it.

Nitrogen is one of the most important elements in the universe. We need to learn about it because our lives and our Earth can be affected by it. So, we need to learn about all the compounds related to Nitrogen and that includes Dinitrogen Pentoxide. 

Did You Know? 

N₂O₅ is indirectly responsible for Ozone layer depletion. 

Conclusion

Chemistry is incomplete without the study of the compounds of Nitrogen. The article discusses very important information that is always asked in examinations and is also important for knowing the compounds of nitrogen. Students can refer to this article on dinitrogen pentoxide for learning about the compound.