Oxides of Nitrogen

Oxides of Nitrogen

Edited By Shivani Poonia | Updated on Jul 02, 2025 06:40 PM IST

Imagine walking through the city center when it is peak traffic time; this would basically imply walking through volumes of smells from all the vehicle fumes. It's also an allusion to one of the major environmental issues related to oxides of nitrogen, popularly known as NOx. These are by-products of Combustion processes in vehicles, power plants, and industrial facilities. The ones including nitric oxide (NO) and nitrogen dioxide (NO2) have huge implications for air pollution, smog, acid rains, etc., and serious negative impacts on the health of people, particularly in the form of respiratory problems.

This Story also Contains
  1. Nitrogen Oxides
  2. Types and Aspects of Nitrogen Oxides
  3. Relevance and Applications in Real Life and Academics
  4. Some Solved Examples
  5. Summary
Oxides of Nitrogen
Oxides of Nitrogen

Nitrogen Oxides

Oxides of nitrogen are a collection of nitrogen-Oxygen compounds that have different oxidation states of nitrogen. The deeper members include nitric oxide, NO, nitrogen dioxide, NO2, nitrous oxide, N2O, and nitrogen trioxide, N2O3. Nitric oxide is a colorless gas that oxidizes in air to yield the reddish-brown toxic gas, nitrogen dioxide. Nitrous oxide is popularly referred to as laughing gas; it represents a greenhouse gas and an anesthetic. Nitrogen trioxide is, however, rather an unstable compound and thus only exists in small quantities. These oxides participate in many different atmospheric chemistry roles, both in natural processes and as anthropogenic pollution.

Types and Aspects of Nitrogen Oxides

Of the nitrogen oxides, there exist a few with different traits and effects. The vast majority of NO is created by high-temperature combustion processes. It is easily oxidized to NO2. Most of the urban smog comes from NO2; more serious health effects can range from simple respiratory problems to asthma. N2O is not quite so reactive but plays a central role in global warming and the destruction of the ozone layer. Another important issue is the formation of nitric acid, HNO3, by NOx reacting with water vapor to form nitric acid resulting in acid rain. Therefore, each of these oxides of nitrogen poses a special problem and needs well-directed programs for control.

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oxides are given in Table given below.

Relevance and Applications in Real Life and Academics

The effects of nitrogen oxides are not limited to environmental degradation; they have broad implications for public health and policy decisions in terms of enforcement of strict emission standards for automobiles and industries in urban centers with high NOx levels and heightened incidents of respiratory diseases. It is also duly important academically, considering how important understanding the study of NOx is for scholars in elucidating the atmospheric chemistry underlying environmental science and engineering solutions to pollution. Such novel technologies have been invented to trim the NOx emissions at their sources, like catalytic converters in cars and SCR systems in industrial plants. In addition, stringent research works have been underway in renewable energies and alternative fuels that would reduce the dependence on fossil fuel and, thereby, NOx generation. These measures entail an interrelation between scientific research and an update in technology with policy initiatives to address challenges in nitrogen oxide.

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Some Solved Examples

Example 1

Question: The set that represents the pair of neutral oxides of nitrogen is:
1.$\mathrm{N}_2 \mathrm{O}$ and $\mathrm{NO}_2$
2. $\mathrm{N}_2 \mathrm{O}$ and $\mathrm{N}_2 \mathrm{O}_3$
3.NO and $\mathrm{N}_2 \mathrm{O}$ Correct
4. (NO and $\mathrm{NO}_2$)

Solution:
NO, and $\mathrm{N}_2 \mathrm{O}$ are neutral oxides, whereas $\mathrm{N}_2 \mathrm{O}_3, \mathrm{NO}_2$ and $\mathrm{N}_2 \mathrm{O}_5$ are acidic oxides. Therefore, the correct answer is option (3): .

Example 2
Question:

The oxidation states of nitrogen in (mathrm{NO}), (mathrm{NO_2}), (mathrm{N_2O}), and (mathrm{NO_3^-}) are in order of:
1.$\mathrm{NO}>\mathrm{NO}_2>\mathrm{N}_2 \mathrm{O}>\mathrm{NO}_3^{-}$
2. $\mathrm{NO_2} > \mathrm{NO_3^-} > \mathrm{NO} > \mathrm{N_2O}$
3. $\mathrm{N_2O} > \mathrm{NO_2} > \mathrm{NO} > \mathrm{NO_3^-}$
4. $\mathrm{NO_3^-} > \mathrm{NO_2} > \mathrm{NO} > \mathrm{N_2O}$

Solution:
The oxidation states of nitrogen in these compounds are:
$\mathrm{NO}$ : +2
$\mathrm{NO_2}$ : +4
$\mathrm{N_2O}$ : +1
$\mathrm{NO_3^-}$ : +5

The decreasing order of the oxidation state of nitrogen is: $\mathrm{NO_3^-} > \mathrm{NO_2} > \mathrm{NO} > \mathrm{N_2O}$. Therefore, the correct answer is option (4).

Example 3
Question
: On heating, lead (II) nitrate gives a brown gas (A). The gas (A) on cooling changes to a colorless solid/liquid (B). (B) on heating with NO changes to a blue solid (C). The oxidation number of nitrogen in solid (C) is:
1. +5
2. +2
3. +3
4. +4

Solution:
The reactions involved are:


$
\mathrm{Pb}\left(\mathrm{NO}_3\right)_2 \xrightarrow{\Delta} \mathrm{PbO}+\underset{\text { Brown gas }}{2 \mathrm{NO}_2}+\frac{1}{2} \mathrm{O}_2(\mathrm{~g})
$


$
\mathrm{NO}_2 \xrightarrow{\text { Cooling }} \mathrm{N}_2 \mathrm{O}_4
$

(B)

$
\mathrm{N}_2 \mathrm{O}_4+\mathrm{NO} \xrightarrow{\Delta} \mathrm{N}_2 \mathrm{O}_3
$ Blue Solid
(C)

The oxidation number of nitrogen in N2O3 is +3. Therefore, the correct answer is option (3).

Summary

Oxides of nitrogen span into a pivot in the knowledge and struggle against air pollution and climate change. The forms range from nitric oxide to nitrous oxide through the different paths on health and environmental effects. NOx mitigation is necessary through research into technological and policy paths; their chemistry holds an insight into how they react to the environment and how these sour effects can be controlled. Measures for minimizing nitrogen oxide should change as much as society itself does.

Frequently Asked Questions (FAQs)

1. 1. What are the major sources of NOx in the environment?

Answer: Nitrogen oxides formed in the first instance as a product of high-temperature combustion. By contrast, major sources are motor vehicles, power plants, industrial processes, and space heating. Whenever fuel is combusted at high temperatures, nitrogen in the air combines with oxygen to form NOx. Some degree of NOx emissions re represents input from natural sources — like lightning or soil microbial activity — though on a far more stretched lower scale compared to man's contribution,.

2. 2. What roles do nitrogen oxides play in air pollution?

solutionseruptions Nitrogen oxides are harmful atmospheric pollutants. In the presence of sunlight, NOx mixes with other volatile organic compounds. These mixtures result in ground-level ozone and hence smog. Again, NO2 reacts with different atmospheric chemicals and results in particulate matter fluent in air quality hence human health. More importantly, NOx causes acid rain that kills plants and destroys buildings and water bodies with time.

3. 3. Nitrogen oxide exposure and health effects

Next are the negative health effects due to the exposure to nitrogen oxides, mainly NO2: Respiratory irritation to the human system caused by short-term exposure, further evidenced by coughing, wheezing, and shortness of breath. Long-term exposure to NO2 may cause chronic diseases, such as respiratory tract infection, reduced lung function, and increased susceptibility to respiratory infection. Target population who are most responsive, meaning NOx exposures seem to target those people who have pre-existing asthma, and other associated respiratory conditions

4. .4. What is going to reduce nitrogen oxide emission?

response : the nitrogen oxide emission shall be reduced by implementing various technological as well as regulative policy measures. the technological solution involved fitting catalytic converters in the vehicles that will convert no gases into less harmful ones. Industrial plants also operate a process called selective catalytic reduction with catalysts which reduces NOx emissions. come in the form of emission standards for vehicles, and industrial processes that shall restrict NOx emissions. proper and effective policies concerning the promotion of renewable sources of energy

5. 5. Why are nitrogen oxides important from the viewpoint of research?

The succeeding lines develop the reasons that make nitrogen oxide studies significant in the academic setting. Information on NOx Chemistry and behavior helps scholars to come up with ideas aimed at countering its effects on the environment. Overall, NOx studies and future research shall aid toward air quality management, management of public health, and climate change mitigation by shouldering innovation in environmental engineering and policy-making toward a cleaner and healthier environment.

6. How does the electronegativity difference between nitrogen and oxygen influence the properties of nitrogen oxides?
The electronegativity difference between nitrogen and oxygen influences the polarity of N-O bonds in nitrogen oxides. This polarity affects properties such as boiling points, solubility, and reactivity. The partial positive charge on nitrogen in these compounds also contributes to their Lewis acidity and ability to form coordination compounds with metals.
7. What is the role of nitrogen oxides in the formation of acid rain?
Nitrogen oxides, particularly NO2, contribute to acid rain formation by reacting with water in the atmosphere to form nitric acid (HNO3). The reaction is: 3NO2 + H2O → 2HNO3 + NO. This nitric acid then falls as precipitation, contributing to the acidity of rain and causing environmental problems such as soil and water acidification.
8. What are oxides of nitrogen and why are they important in chemistry?
Oxides of nitrogen are compounds formed by nitrogen and oxygen atoms. They are important in chemistry because they play significant roles in atmospheric chemistry, industrial processes, and biological systems. These compounds exhibit a wide range of oxidation states for nitrogen, demonstrating the element's variable valency.
9. What is the environmental impact of nitrogen oxides?
Nitrogen oxides, particularly NO and NO2 (collectively called NOx), have significant environmental impacts. They contribute to the formation of acid rain, smog, and ground-level ozone. NOx also plays a role in the depletion of the ozone layer and can cause respiratory problems in humans and animals.
10. How do nitrogen oxides contribute to the formation of photochemical smog?
Nitrogen oxides, especially NO2, contribute to photochemical smog formation by reacting with volatile organic compounds (VOCs) in the presence of sunlight. This reaction produces ground-level ozone and other secondary pollutants, leading to the characteristic haze and air quality issues associated with smog.
11. Why is nitrous oxide (N2O) called "laughing gas"?
Nitrous oxide (N2O) is called "laughing gas" due to the euphoric effects it produces when inhaled in small amounts. It causes a feeling of giddiness and can induce laughter, hence the name. However, it's important to note that N2O is primarily used as an anesthetic and analgesic in medical settings.
12. Why is nitric oxide (NO) considered a free radical?
Nitric oxide (NO) is considered a free radical because it has an unpaired electron in its molecular orbital. This unpaired electron makes NO highly reactive and gives it paramagnetic properties. The free radical nature of NO is crucial for its biological functions, such as neurotransmission and vasodilation.
13. How many stable oxides of nitrogen exist?
There are seven stable oxides of nitrogen: nitrous oxide (N2O), nitric oxide (NO), dinitrogen trioxide (N2O3), nitrogen dioxide (NO2), dinitrogen tetroxide (N2O4), dinitrogen pentoxide (N2O5), and nitrous anhydride (N2O2). Each has unique properties and applications in various fields.
14. Why does nitrogen form multiple oxides while other elements in Group 15 typically form fewer?
Nitrogen forms multiple oxides due to its ability to exhibit variable oxidation states, ranging from +1 to +5. This is because nitrogen has a small atomic size and high electronegativity compared to other Group 15 elements, allowing it to form stable bonds with oxygen in various configurations.
15. What is the difference between nitrogen dioxide (NO2) and dinitrogen tetroxide (N2O4)?
Nitrogen dioxide (NO2) is a reddish-brown gas, while dinitrogen tetroxide (N2O4) is a colorless solid at low temperatures. They exist in equilibrium, with N2O4 dissociating into NO2 at higher temperatures. NO2 is a paramagnetic molecule with an unpaired electron, while N2O4 is diamagnetic.
16. How does the structure of nitrous oxide (N2O) contribute to its properties?
Nitrous oxide (N2O) has a linear structure with nitrogen atoms at both ends and oxygen in the middle. This arrangement results in a relatively stable molecule with a low dipole moment. The structure contributes to its inertness at room temperature and its ability to act as a weak oxidizing agent.
17. How does the bond order in NO+ compare to that in NO and NO-?
The bond order in NO+ is 3, in NO is 2.5, and in NO- is 2. This trend occurs because removing an electron from NO to form NO+ increases the bond order, while adding an electron to form NO- decreases it. The higher bond order in NO+ results in a shorter and stronger bond compared to NO and NO-.
18. How does the Lewis structure of NO2 explain its properties?
The Lewis structure of NO2 shows a central nitrogen atom with a double bond to one oxygen and a single bond to the other, plus an unpaired electron. This structure explains NO2's paramagnetism, its ability to dimerize to form N2O4, and its high reactivity due to the unpaired electron.
19. What is the role of nitrogen oxides in the nitrogen cycle?
Nitrogen oxides play crucial roles in the nitrogen cycle. They are produced by lightning and certain bacteria in the soil. These compounds can be converted into nitrates, which plants can absorb. Some bacteria can also convert nitrogen oxides back into atmospheric nitrogen, completing the cycle.
20. How do nitrogen oxides affect human health?
Nitrogen oxides, particularly NO2, can have harmful effects on human health. They can irritate the respiratory system, worsen asthma symptoms, and increase susceptibility to respiratory infections. Long-term exposure to high levels of NO2 can lead to the development of respiratory diseases.
21. Why is dinitrogen pentoxide (N2O5) considered the anhydride of nitric acid?
Dinitrogen pentoxide (N2O5) is considered the anhydride of nitric acid because it reacts with water to form nitric acid (HNO3). The reaction is: N2O5 + H2O → 2HNO3. This property makes N2O5 an important compound in the industrial production of nitric acid.
22. How does the stability of nitrogen oxides change with increasing oxidation state of nitrogen?
Generally, the stability of nitrogen oxides decreases as the oxidation state of nitrogen increases. For example, N2O (nitrogen oxidation state +1) is relatively stable, while N2O5 (nitrogen oxidation state +5) is highly reactive and unstable. This trend is due to the increasing energy required to remove electrons from nitrogen as its oxidation state increases.
23. What is the significance of NO in biological systems?
Nitric oxide (NO) is a crucial signaling molecule in biological systems. It acts as a neurotransmitter, regulates blood pressure by dilating blood vessels, and plays a role in the immune system's response to pathogens. Its discovery and importance in biology led to the Nobel Prize in Physiology or Medicine in 1998.
24. How do nitrogen oxides participate in ozone depletion?
Nitrogen oxides, particularly NO, participate in ozone depletion through a catalytic cycle. NO reacts with ozone (O3) to form NO2 and O2. The NO2 then reacts with atomic oxygen to regenerate NO and form O2. This cycle can repeat many times, allowing a single NO molecule to destroy multiple ozone molecules.
25. Why is the N-N bond in N2O unusually long compared to other N-N bonds?
The N-N bond in N2O is unusually long (1.13 Å) compared to the N-N bond in N2 (1.09 Å) because it's a single bond with some double bond character due to resonance. The presence of the oxygen atom and the linear structure of N2O contribute to this elongation by affecting the electron distribution in the molecule.
26. How does the acidity of oxoacids of nitrogen relate to the oxidation state of nitrogen?
The acidity of oxoacids of nitrogen generally increases with the oxidation state of nitrogen. For example, nitrous acid (HNO2, N oxidation state +3) is a weaker acid than nitric acid (HNO3, N oxidation state +5). This trend is due to the higher oxidation state allowing for greater delocalization of the negative charge in the conjugate base, stabilizing it and making the acid stronger.
27. What is the role of NO2 in the industrial production of nitric acid?
NO2 plays a crucial role in the industrial production of nitric acid through the Ostwald process. In this process, ammonia is oxidized to NO, which is further oxidized to NO2. The NO2 is then absorbed in water to form nitric acid. The overall reaction is: 4NH3 + 5O2 → 4NO + 6H2O, followed by 2NO + O2 → 2NO2, and finally 3NO2 + H2O → 2HNO3 + NO.
28. How does the molecular geometry of NO3- affect its properties?
The nitrate ion (NO3-) has a trigonal planar geometry with the nitrogen at the center and three oxygen atoms arranged symmetrically around it. This geometry results in a delocalized negative charge across all three oxygen atoms, contributing to the ion's stability and its behavior as a weak base. The planar structure also influences its ability to coordinate with metal ions in various compounds.
29. Why is NO2 colored while N2O4 is colorless?
NO2 is colored (reddish-brown) because it absorbs light in the visible spectrum due to its unpaired electron, which allows for electronic transitions. N2O4, on the other hand, is colorless because all its electrons are paired, and the energy required for electronic transitions is outside the visible spectrum. The color change between NO2 and N2O4 is an example of thermochromism.
30. How does the reactivity of N2O compare to other nitrogen oxides?
N2O (nitrous oxide) is generally less reactive than other nitrogen oxides. It's relatively inert at room temperature and doesn't react readily with water or oxygen. This stability is due to its electronic structure and the strong triple bond between the nitrogen atoms. However, at high temperatures, N2O can act as an oxidizing agent.
31. What is the importance of NOx in atmospheric chemistry?
NOx (NO and NO2) plays a crucial role in atmospheric chemistry. It participates in the formation of tropospheric ozone, contributes to the formation of acid rain, and affects the concentration of hydroxyl radicals (OH) in the atmosphere. NOx also influences the Earth's radiative balance and plays a role in the chemistry of the stratospheric ozone layer.
32. How does the bond angle in NO2- compare to that in NO2, and why?
The bond angle in NO2- (nitrite ion) is approximately 115°, while in NO2 it's about 134°. The smaller angle in NO2- is due to greater electron repulsion from the additional electron, which occupies a molecular orbital with significant antibonding character. In NO2, the unpaired electron occupies a non-bonding orbital, resulting in less repulsion and a wider angle.
33. What is the significance of the N-O bond lengths in different nitrogen oxides?
The N-O bond lengths in nitrogen oxides provide insight into the bond order and electronic structure of these molecules. For example, the N-O bond in NO+ is shorter than in NO, which is shorter than in NO-. These differences reflect the changing bond orders (3, 2.5, and 2 respectively) and electron distribution in these species.
34. How does the concept of resonance apply to nitrogen oxides?
Resonance is important in understanding the structure and properties of several nitrogen oxides. For example, NO2 can be represented by two resonance structures where the double bond alternates between the two oxygen atoms. This resonance contributes to the stability of the molecule and explains its observed bond lengths and angles.
35. Why is N2O5 considered a mixed anhydride?
N2O5 is considered a mixed anhydride because it can be viewed as a combination of nitric acid anhydride (NO2-O-NO2) and nitrous acid anhydride (NO-O-NO3). This dual nature is reflected in its reactions; for example, it can produce both nitric acid and nitrous acid depending on the conditions of hydrolysis.
36. How does the electron affinity of oxygen affect the formation of nitrogen oxides?
The high electron affinity of oxygen plays a crucial role in the formation of nitrogen oxides. Oxygen's ability to attract electrons allows it to form strong bonds with nitrogen, despite nitrogen's relatively high electronegativity. This results in a range of stable nitrogen oxide compounds with various oxidation states of nitrogen.
37. What is the relationship between the structure of NO and its biological function?
The structure of NO, with its unpaired electron, is key to its biological function. The small size and neutral charge of NO allow it to diffuse easily through cell membranes. Its unpaired electron makes it reactive, enabling it to participate in signaling processes and react with other biological molecules, such as in the regulation of blood pressure through interaction with the enzyme guanylate cyclase.
38. How does the concept of hybridization apply to nitrogen in different nitrogen oxides?
Hybridization of nitrogen varies among different nitrogen oxides, affecting their geometry and properties. For example, in NO2, nitrogen is sp2 hybridized, resulting in a bent structure. In N2O, the central nitrogen is sp hybridized, contributing to its linear structure. Understanding hybridization helps explain the molecular geometries and reactivity of these compounds.
39. Why is NO2 a stronger oxidizing agent than NO?
NO2 is a stronger oxidizing agent than NO because nitrogen in NO2 has a higher oxidation state (+4) compared to NO (+2). This means NO2 has a greater tendency to gain electrons and be reduced. Additionally, the electron affinity of NO2 is higher than that of NO, further enhancing its oxidizing power.
40. How does the dipole moment of different nitrogen oxides affect their properties?
The dipole moment of nitrogen oxides varies, affecting their physical and chemical properties. For example, N2O has a small dipole moment due to its linear structure, contributing to its low boiling point and limited solubility in water. In contrast, NO2 has a larger dipole moment, making it more soluble in water and more reactive in certain chemical processes.
41. What is the significance of the N-N bond in hyponitrous acid (H2N2O2)?
The N-N bond in hyponitrous acid (H2N2O2) is significant because it's relatively weak, making the compound unstable. This weak bond is due to repulsion between the lone pairs on the nitrogen atoms. The instability of hyponitrous acid leads to its easy decomposition, which is important in understanding its chemistry and potential applications.
42. Why is NO considered an odd-electron molecule, and how does this affect its properties?
NO is considered an odd-electron molecule because it has 11 valence electrons, resulting in an unpaired electron. This unpaired electron makes NO paramagnetic and highly reactive. It also explains NO's ability to form dimers (N2O2) and its importance in biological processes where it can easily donate or accept electrons.
43. How does the concept of formal charge help in understanding the structure of nitrogen oxides?
Formal charge calculations help in understanding the most stable structures of nitrogen oxides. For example, in NO3-, the structure with a central nitrogen bonded to three oxygens (one double bond and two single bonds) minimizes formal charges, explaining its observed structure. This concept is crucial for predicting the most likely bonding arrangements in these molecules.
44. How does the presence of unpaired electrons in some nitrogen oxides affect their magnetic properties?
The presence of unpaired electrons in some nitrogen oxides, such as NO and NO2, makes these molecules paramagnetic. This means they are attracted to magnetic fields. In contrast, nitrogen oxides without unpaired electrons, like N2O or N2O4, are diamagnetic. These magnetic properties are important in spectroscopic studies and in understanding the reactivity of these compounds.
45. Why is the N-O bond length in NO+ shorter than in NO?
The N-O bond length in NO+ is shorter than in NO because NO+ has a higher bond order (3) compared to NO (2.5). The removal of an electron from NO to form NO+ occurs from an antibonding orbital, increasing the strength of the bond and decreasing its length. This illustrates the relationship between bond order and bond length in molecular ions.
46. How does the concept of isoelectronic species apply to nitrogen oxides?
Isoelectronic species have the same number of electrons but different nuclear charges. For example, NO+ and CO are isoelectronic, both having 14 electrons. Understanding isoelectronic relationships helps predict similarities in properties and structures among different species, including nitrogen oxides and related compounds

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