Dinitrogen Pentoxide

Definition 

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. 

Dinitrogen pentoxide is the anhydride form of nitric acid which can exist as a colourless crystal. It melts at 30-degree Celcius. 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 (NO)

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 - 

  • 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 16 / 2 = 8 bonds.

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

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Now let us indicate the initial bonds formed between Nitrogen and Oxygen -

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Now that we have 6 bonds, we still need 2 more bonds which we can put here -

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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 electro-positive 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 how the Lewis dot diagram of N₂O₅ looks like -

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


Key Takeaways

  • N₂O₅ is named Dinitrogen Pentoxide because it has 2 Nitrogen atoms and 5 Oxygen atoms.

  • The total number of valence electrons if we take into account each of the atoms in N₂O₅ is 40 - 10 of two nitrogens and 30 of 5 Oxygens

  • While drawing the Lewis Dot structure of N₂O₅, you must remember the fact that Oxygen is electronegative.


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-degree celsius.

  • Upon being melted at 30-degree celsius, it transforms into a yellowish liquid.

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

N2O5 Is an Acidic Anhydride 

Anhydride is that 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 an acid too. If HNO₃ can be dehydrated to obtain N₂O₅, 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 NO 

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 +1 charge while the NO₃ atom has -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?

Key Takeaways

  • Dinitrogen Pentoxide is colourless. Up to 30-degree Celsius, it remains solid. Then it starts melting. At 40 degree Celsius, it explodes and decomposes into NO₂ and O₂.

  • It is the dehydrated form of nitric acid.

  • If added water, it can again turn into nitric acid.

  • Since it contains no water, it is known as anhydride.


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) mol L⁻¹/x] 

The actual formula looks like this - 

Rate of decomposition =  ½ { - Delta N₂O₅ / Delta T]

Why ½? Because we have written 2NO₂. Why minus sign? Because the concentration is getting depleted.

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

¼ {Delta NO₂ / Delta T }

Why ¼? Because we have written 4 NO₂? Why +¼ and not - ¼ ? 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 that N₂O₅ is indirectly responsible for the Ozone layer depletion? Chemistry is incomplete without the study of the compounds of Nitrogen.

FAQ (Frequently Asked Questions)

1. Is Dinitrogen Pentoxide Ionic or Covalent ?

Ans - N2O5 is made up of two nonmetals - Oxygen and Nitrogen. The ionic charge of Oxygen is -2 and the ionic charge of Nitrogen is -3. When two nonmetals or two negatively charged atoms try to form bonds, they always form covalent bonds. Hence, Dinitrogen Pentoxide is not ionic - it is covalent.

2. Is Dinitrogen Pentoxide Acidic or Basic?

Ans. Dinitrogen Pentoxide is acidic. It is formed by dehydrating nitric acid. Hence, if we add water we can get back HNO3. So Dinitrogen Pentoxide is acidic.

3. How is Dinitrogen Pentoxide Formed?

Ans. N2O5 can be prepared by dehydrating nitric acid with Phosphorus pentoxide. The reaction will look like this -

P4O10 + 12HNO3 → 4H3PO4 + 6N2O5

4. What is Dinitrogen Pentoxide Decomposition ?

Ans. Decomposition of N2O5 means that, if heated at 40-degree celsius and more, Dinitrogen Pentoxide will decrease in composition and it will turn into NO2 and O2. It looks like this -

2N2O5 → 4NO2 + O2

5. What is the Chemical Formula of Dinitrogen Pentoxide ?

Ans - The chemical formula of Dinitrogen Pentoxide is N2O5.

6. Does Dinitrogen Pentoxide React with Water?

Ans. Yes, if you add water to Dinitrogen pentoxide, it will turn into nitric acid. This is what proves that Dinitrogen Pentoxide is acidic.

7. Is Dinitrogen Pentoxide Gas?

Ans. No, Dinitrogen Pentoxide is a colourless, crystalline solid. When heated, it transforms into NO2.

8. Is Dinitrogen Pentoxide Binary?

Ans. Yes, Dinitrogen Pentoxide is made up of atoms of just two elements - Nitrogen and Oxygen. Hence N2O5 is a binary compound. 

9. What is Dinitrogen Pentoxide Used for?

Ans. Dinitrogen Pentoxide is mainly used as a nitrating agent. It can also be used to make explosives. However, people don’t use N2O5 much today.