What do a dentist and a soldier in the trenches in the 20th century have in common? They most likely have some nitrous oxide in their possession. Of course, they are probably not going to refer to it as that, but rather they will say "laughing gas". You might have heard of it, and the truth is that it's everywhere... sometimes even too much. Laughing gas is known for its euphoric as well as anaesthetic effects. That is why you will find it everywhere, in both medicinal purposes and possibly even a contributor to climate change.
But what exactly is it? Here we will deep dive into its structure and formula to discuss some of its properties and biological effects. You will then see how its structure lends itself to having these properties.
- This article is about nitrous oxide.
- Firs, we will see the nitrous oxide formula and Lewis structure determination.
- Then, the chemical and Physical properties of the molecule.
- Next, we will analyse the uses of the gas in many fields.
- To end, we will see its biological effects.
Nitrous Oxide Definition
Here we will discuss on some commonly known facts of nitrous oxide, and what it is known for. So, what is nitrous oxide?
Nitrous oxide, chemically known as Dinitrogen Monoxide is a colourless gas with a sweet odour. The chemical formula of Nitrous oxide is N2O.
You might have heard of "laughing gas", and it will be interesting for you to know that that term often refers to nitrous oxide. In fact, the terms are often used interchangeably.
The term "laughing gas" was termed after its medical uses and euphoric effects when inhaled. It used to be commonly used as a sedative during surgeries and other procedures on patients.
To briefly introduce the gas, it is worth mentioning that it is inert. Many oxides form acidic or basic solutions and salts when dissolved in water, but not nitrous oxide. This makes nitrous oxide a very interesting oxide which remains inert under different conditions, which gives rise to its many uses. We will discuss more on the properties of the molecule later on.
Nitrous Oxide Formula and Structure
Here we will discuss the chemical formula and structural properties of nitrous oxide. We will first cover the formula of the inorganic oxide and later discuss the lewis structure of the compound.
Formula
The formula of nitrous oxide is N2O. But what does this mean to the structure of the molecule?
Since in the formula of the compound, there are two nitrogen atoms and a single oxygen atom, there can be a number of possibilities these substituent atoms can come together potentially. Yet, there is only one structure that is valid within the frames of chemistry.
Lewis Structure
Here we will discuss the Lewis structure of nitrous oxide and how we get to the structures which are representative of the electronic structures of the molecule.
So, we know that the molecule has two nitrogen atoms and an oxygen atom.
There are two possibilities for writing the structure of Nitrous Oxide. The NNO form wherein one of the nitrogens forms the central atom flanked by the second nitrogen and oxygen on either side. The other way of writing is the NON-form where the oxygen is the central atom flanked by the nitrogens on either side.
Of the two structures, the NNO is considered to be more stable and favoured. The reason is the formal charge on oxygen. The most electronegative atom should bear a negative charge or at least should be less positive. In nitrous oxide, the oxygen atom is the most electronegative atom. When we write a structure placing the central atom as oxygen, the oxygen atom bears a +2 charge which is not favourable and the molecule will not be stable. Wherever you observe in chemistry, all the molecules, atoms and ions aim for stability and favour conditions that lead them to stability. Thus, the NON-structure is not stable. Let us have a look at both possibilities for better comprehension.
Another likely explanation for the stability of the NNO structure is the bond order. The more the bond order, the more stability. The bond order of the N-N bond is 2.5(nearly 3) while the N-O bond order is 1.6(nearly 2). The structure that has N-N bonds is favoured, hence the NNO possibility. (Note: Compare this with the triple bond which is stronger than the double bond which is stronger than the single bond. The triple bond has the bond order of 3, the double bond has 2 and the single bond has 1, hence the order of stability)
Fig. 1: The NON and NNO- possibilities, Nitrous Oxide, Archana Tadimeti, Vaia Originals
To understand how formal charges are calculated, head over to this article on Formal Charge.
So if we place nitrogen as the central atom, and then the oxygen on one side and the other nitrogen on the other side of the central atom, we can start creating bond structures.
The first thing you can do is draw out the dot electron form of each atom and then start creating covalent bonds.
Remember that covalent bonds are bonds where electrons are shared, so from the dot structures, two dots will need to make up a single bond.
Nitrous oxide can exist in three different forms. Of the three, structure A is more favoured (major contributor)[1] because of the low magnitude of charges on atoms and most importantly, the negative charge is on the most electronegative atom(oxygen) in the structure. An electronegative atom handles the negative charge with ease. Therefore, you can write structure A as the lewis structure of nitrous oxide when asked in your exam.
Structure C is less favoured due to the large magnitude of formal charges and positive charge on the electronegative oxygen.
When writing the Lewis structures of nitrous oxide, it is important to mention the formal charges on each atom. Why?
Notice structure A, the central nitrogen forms 4 bonds (a triple bond with the other N and a single bond with oxygen). But, nitrogen can form only 3 bonds. So, it means that in this case nitrogen contributed its lone pair of electrons towards bond formation with oxygen. Hence, the positive charge. In the same structure, oxygen bears a negative charge because it didn't form the usual 2 bonds that it can form. A similar explanation holds true for all the other structures.
Therefore, if you don't mention the charges on the atoms of the following structures, the structures might be invalid.
Fig. 2: Lewis structures of nitrous oxide, Archana Tadimeti, Vaia Originals
One must bear in mind two things while writing Lewis structures for tricky chemical species like that of nitrous oxide-
1. A Lewis structure with the lowest magnitude of formal charges must be chosen as the most favourable structure
2. If two Lewis structures have the same magnitude of formal charges, choose the one that has a negative charge on the more electronegative atom.
Using this structure but moving the electrons around can create valid Lewis structures. In the diagram above, you can see how two different valid Lewis structures for nitrous oxide by moving some electrons around.
A valid Lewis structure of nitrous oxide (Structure A) will consist of the central atom having no lone pairs, and four bonds spaced asymmetrically. This asymmetry is caused by one of the peripheral atoms being singly bonded, while the other has a triple bond with the central atom. When the central nitrogen atom has four bonds around itself and no lone pairs, then the octet rule (the tendency of atoms to have 8 electrons in the outermost shell) is satisfied, which creates a valid structure. This means that the peripheral nitrogen or oxygen will either have a single bond with the central nitrogen and three pairs of lone electrons or have a triple bond with the central nitrogen and have a single pair of lone electrons. But, as discussed earlier if the triple bond is between the central nitrogen and oxygen, oxygen will have a positive formal charge, and it is not favourable.
Through this method, we can arrive at the accepted structure of nitrous oxide, which exists in three different conformations, of which structure A is the most favourable. Using electron dot structures and principles of Lewis structures, we can generate appropriate and valid structures of nitrous oxide.
Fig. 3_Fig. 3: Nitrous Oxide, Archana Tadimeti, Vaia Originals
Nitrous Oxide Properties
Here we will discuss the properties of nitrous oxide. These can be divided into the physical and chemical properties of the molecule, which all stem from the structure of nitrous oxide, as well as how the molecules of N2O interact with themselves.
Physical Properties
The physical properties of nitrous oxide can be explained based on molecular interactions.
Nitrous oxide is a gas at room temperature and standard pressure. This is because of weak intermolecular forces. Nitrous oxide lacks hydrogen bonding, and VanderWaal's interactions exist in a liquid state. However, Nitrous oxide can be liquified when subjected to high pressures and low temperatures.
- Nitrous oxide is 1.5 times denser than air. Its molecular weight is 44g/mol.
- It is inert, neutral and fairly soluble in water. That is to say that it is an oxide that does not create any acidic or basic environment when dissolved in water.
- It is a colourless gas with a pleasant odour and taste.
Chemical Properties
Here we will discuss the chemical properties of nitrous oxide.
At a temperature of 873 K, the molecule can decompose into nitrogen and oxygen gases. The decomposition of nitrous oxide is crucial in different chemical environments as it is one of the most important gases contributing towards climate change.
Nitrous oxide is non-combustible, but supports combustion in the presence of oxygen.
Nitrous oxide is a strong oxidising agent.
Laughing gas is a greenhouse gas
Did you know that Nitrous oxide is a greenhouse gas and is more potent than carbon dioxide? This is because nitrous oxide can stay longer in the atmosphere. Not just that, nitrous oxide is also responsible for ozone depletion.[4] It also contributes to a phenomenon known as Radioactive Forcing where in it traps the heat coming from the sun and thus warming the earth.
Sources of Nitrous oxide emissionThe man-made/anthropogenic sources of nitrous oxide include Livestock production (emissions from the cattle feed), synthetic fertilisers used for crop production, burning of fossil fuels etc., These sources pose a severe challenge to curbing nitrous oxide emissions because farming and agriculture are the heart of the very human existence. Can the world survive without them?
It is difficult, but not impossible. How can we contribute our part to saving the earth from nitrous oxide emissions?
By reducing the use of nitrogen-based fertilisers and using other types instead.
Urease inhibitors: Urease breaks down the N-fertiliser urea to Ammonia, causing wastage and in turn building the need to use the excess Urea. Increased usage of urea leads to elevated levels of nitrous oxide production. So, to get the maximum benefit from a small quantity of urea, Urease inhibitors are used in New Zealand[2] that will inhibit the production of Urease. Therefore, the urea used will be consumed to its maximum without any wastage, thus minimising the need for extra urea.
Precision farming: Using information technology, farmers can make informed decisions on when and where fertiliser is needed.[3] This latest technology-based farming helps in increased crop production and improves the efficacy and efficiency of fertilisers, thus helping us use only the required amount.[3]
“ The greatest threat to our planet is the belief that someone else will save it.”
-Robert Swan
Let us do our bit for the planet as teachers, scientists, engineers, farmers and human beings. Science is a powerful tool that has the potential to change the world. Think of how you can positively impact the world with your science education.
Nitrous Oxide Effects
Nitrous Oxide has some adverse biological effects on human body. It can trigger molecular damage to the cell and lead to mutations within DNA. This often results in mental impairment.
It can also lead to other biomedical implications to the body, such as oxygen deficiency and vitamin B12 depletion. It can have "euphoric" effects and an antianxiety sensation.
Nitrous oxide is also known to negatively impact the human immune system.
Nitrous Oxide Uses
Nitrous Oxide has a wide-range of applications in various industries. Given, below are a collection of the most common uses of nitrous oxide.
| Industry | Application of Nitrous oxide |
| Human and veterinary medicine | Anaesthetic |
| Dentistry | Anaesthetic in combination with oxygenrelieves from pain and anxiety |
| Food | Aerosol propellent/ foaming agent for whipped cream |
| Chemical | Synthesis of nitrogen-based organic compounds like Azo dyes |
| Aerospace technology | Rocket fuel |
Table 1: Some applications of nitrous oxide in the industry.
Getting past the uses of nitrous oxides can be used in, as well as knowing the formula and structures the molecule adopts, you should be well-equipped to fully grasp this topic. Now you can tell people what laughing gas really is, and all of its applications and impacts.
Nitrous Oxide - Key takeaways
- Nitrous oxide formula is N2O.
- The Lewis structure has a nitrogen as a central atom, which has 4 bonds and no lone pairs.
- It has weak intermolecular interactions which makes it a gas.
- Chemical properties include it being inert, and having a violent decomposition under high temperatures.
- It is mostly used within the medical industry but also has biological side effects.
References
- https://chemistry.stackexchange.com/questions/29657/what-are-the-correct-resonance-structures-of-nitrous-oxide
- https://www.agmatters.nz/actions/reduce-nitrogen-fertiliser/
- https://www.sciencedirect.com/topics/earth-and-planetary-sciences/precision-agriculture
- https://ui.adsabs.harvard.edu/abs/2015AGUFM.B14A..01R/abstract
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