Oxides of Nitrogen

Nitrogen oxides are gases composed of nitrogen and oxygen. The most toxicologically significant compounds are nitric oxide (NO) and nitrogen dioxide (NO₂). Other gases in this group include nitrous oxide (N₂O) and dinitrogen pentoxide (N₂O₅). Nitrogen oxides are formed when nitrogen reacts with oxygen.

1.0Introduction 

Nitrogen oxide is a compound consisting of nitrogen and oxygen atoms. Molecular nitrogen (N₂), diatomic and relatively inert, makes up approximately 80% of our air. However, the element nitrogen (N) can be reactive as a single atom, with ionization levels (valence states) ranging from plus one to plus five. This allows nitrogen to form various oxides. In the Niels Bohr atom model, the valence state corresponds to the number of electrons that are either deficient (resulting in a positive valence) or surplus (resulting in a negative valence) in the ion compared to the neutral molecule 

2.0 What are the Sources Oxides Of Nitrogen?

• Natural Sources of Nitrogen 

Lightning bolts are a natural source of nitrogen oxides. During a lightning strike, the intense heat and energy released can cause nitrogen and oxygen in the air to react, forming various nitrogen oxides including, nitric oxide (NO) and nitrogen dioxide (NO₂). These nitrogen oxides are then dispersed into the atmosphere, contributing to atmospheric chemistry and potentially affecting air quality and the environment.

• Human Sources of Nitrogen Oxides

Human activities contribute significantly to the production of nitrogen oxides (NOₓ). Nitrogen and oxygen do not react at average temperatures, but in high temperatures, such as during combustion processes, they combine to form nitric oxide (NO). This occurs prominently in coal and oil combustion at power plants and gasoline combustion in automobiles. Both sources contribute nearly equally to nitrogen oxide emissions

3.0Oxides of Nitrogen

Dinitrogen Oxide (N₂O)

Dinitrogen oxide, commonly known as laughing gas, is a colourless, non-flammable gas with neutral properties. It is generated through the thermal decomposition of ammonium nitrate.

NH₄NO₃ → 2H₂O + N₂O

Dinitrogen Trioxide (N₂O₃)

Dinitrogen trioxide is a deep blue, acidic solid that is stable only in liquid or solid phases at low temperatures. As the temperature increases, it decomposes into its constituent gases. It is produced by combining equal amounts of nitric oxide and nitrogen dioxide and cooling the mixture below −21 °C.

• NO + NO₂→N₂O₃

Nitrogen Monoxide (NO)

Nitrogen monoxide is a colourless gas belonging to a class of diatomic molecules with a lone valence electron. It is prepared by reducing dilute nitric acid with copper:

• 3H₂SO₄ + 2NaNO₂ + 2FeSO₄ → 2NaHSO₄  + Fe₂(SO₄)₃ + 2H₂O + 2NO₃

Nitrogen Dioxide (NO₂)

Nitrogen dioxide is a reddish-brown poisonous gas with a pungent smell, significantly contributing to air pollution. It is acidic and has a +4 oxidation state of nitrogen. The thermal decomposition of metal nitrates produces nitrogen dioxide:

• 2Pb(NO₃)₂  →  4NO₂ + 2PbO + O₂

Dinitrogen Tetroxide (N₂O₄)

Dinitrogen tetroxide is a colourless solid that exists in equilibrium with nitrogen dioxide. It is a powerful oxidizing agent and is used in the production of various chemical compounds:

• ${\mathrm{N}}_2{\mathrm{O}}_4\rightleftharpoons 2{\mathrm{NO}}_2$

    Dinitrogen Pentoxide (N₂O₅)

Dinitrogen pentoxide is a colourless solid that sublimes just above room temperature. It is an unstable and potentially hazardous oxidizing agent. It is used as a nitrating agent in chloroform solutions and is produced by dehydrating nitric acid with phosphorus (V) oxide:

• P₄O₁₀ + 12HNO₃ → 4H₃PO₄ + 6N₂O₅             

4.0The Role of Nitrogen Oxides

Nitrogen oxides play significant roles in both beneficial and harmful contexts for living organisms.

• Dinitrogen Monoxide (N₂O): Known as laughing gas, dentists widely use this anaesthetic to provide pain relief and sedation during dental procedures. It provides pain relief and sedation during dental procedures.
• Nitrogen Dioxide (NO₂): This compound is harmful and toxic. It combines with haemoglobin molecules in the blood, preventing the release of oxygen throughout the body. Nitrogen dioxide is primarily released from automobile emissions and contributes significantly to air pollution.
• Nitrate (NO₃^-): Nitrate is a polyatomic ion that is a key nutrient for plants and plays an important role in the nitrogen cycle. However, excessive nitrate levels in water sources can cause environmental problems like eutrophication.
• Unstable Nitrogen Oxides: These compounds are used in specialized applications, such as space travel. Their reactivity and energetic properties make them suitable for propulsion systems and other advanced technologies.