- Oxidation numbers for nitrogen and oxygen in their oxides
- Different formulations and nomenclatures
- Nitrous oxide (N 2 O)
- Nitrogen dioxide and tetroxide (NO
- Dinitrogen pentoxide (N
- References
The nitrogen oxides are essentially gaseous inorganic compounds containing from nitrogen and oxygen. Its group chemical formula is NO x, indicating that oxides have different ratios of oxygen and nitrogen.
Nitrogen heads group 15 on the periodic table, while oxygen heads group 16; both elements are members of period 2. This closeness is the cause that in oxides the N – O bonds are covalent. Thus, the bonds in nitrogen oxides are covalent.
All these bonds can be explained using the molecular orbital theory, which reveals the paramagnetism (an unpaired electron in the last molecular orbital) of some of these compounds. Of these, the most common compounds are nitric oxide and nitrogen dioxide.
The molecule in the upper image corresponds to the angular structure in the gas phase of nitrogen dioxide (NO 2). In contrast, nitric oxide (NO) has a linear structure (considering sp hybridization for both atoms).
Nitrogen oxides are gases produced by many human activities, from driving a vehicle or smoking cigarettes, to industrial processes such as polluting waste. However, naturally NO is produced by enzymatic reactions and lightning action in electrical storms: N 2 (g) + O 2 (g) => 2NO (g)
The high temperatures of the rays break the energy barrier that prevents this reaction from occurring under normal conditions. What energy barrier? That formed by the triple bond N≡N, making the N 2 molecule an inert gas in the atmosphere.
Oxidation numbers for nitrogen and oxygen in their oxides
The electron configuration for oxygen is 2s 2 2p 4, needing only two electrons to complete the octet of its valence shell; that is, it can gain two electrons and have an oxidation number equal to -2.
On the other hand, the electron configuration for nitrogen is 2s 2 2p 3, being able to gain up to three electrons to fill its valence octet; for example, in the case of ammonia (NH 3) it has an oxidation number equal to -3. But oxygen is much more electronegative than hydrogen and "forces" nitrogen to share its electrons.
How many electrons can nitrogen share with oxygen? If you share the electrons in your valence shell one by one, you will reach the limit of five electrons, corresponding to an oxidation number of +5.
Consequently, depending on how many bonds it forms with oxygen, the oxidation numbers of nitrogen vary from +1 to +5.
Different formulations and nomenclatures
Nitrogen oxides, in increasing order of nitrogen oxidation numbers, are:
- N 2 O, nitrous oxide (+1)
- NO, nitric oxide (+2)
- N 2 O 3, dinitrogen trioxide (+3)
- NO 2, nitrogen dioxide (+4)
- N 2 O 5, dinitrogen pentoxide (+5)
Nitrous oxide (N 2 O)
Dotted lines in the structure indicate double bond resonance. Like all atoms, they have sp 2 hybridization, the molecule is flat, and the molecular interactions are effective enough for nitrogen trioxide to exist as a blue solid below -101ºC. At higher temperatures it melts and dissociates into NO and NO 2.
Why is it dissociated? Because the oxidation numbers +2 and +4 are more stable than +3, the latter present in the oxide for each of the two nitrogen atoms. This, again, can be explained by the stability of the molecular orbitals resulting from the disproportion.
In the image, the left side of N 2 O 3 corresponds to NO, while the right side to NO 2. Logically, it is produced by the coalescence of the previous oxides at very cold temperatures (-20ºC). N 2 O 3 is nitrous acid anhydride (HNO 2).
Nitrogen dioxide and tetroxide (NO
NO 2 is a reactive, paramagnetic, brown or brown gas. As it has an unpaired electron, it dimerizes (binds) with another gaseous NO 2 molecule to form nitrogen tetroxide, a colorless gas, establishing an equilibrium between both chemical species:
2NO 2 (g) <=> N 2 O 4 (g)
It is a poisonous and versatile oxidizing agent, capable of disproportionate in its redox reactions in the ions (oxoanions) NO 2 - and NO 3 - (generating acid rain), or in NO.
Likewise, NO 2 is involved in complex atmospheric reactions causing variations in ozone (O 3) concentrations at terrestrial levels and in the stratosphere.
Dinitrogen pentoxide (N
When it hydrates, it generates HNO 3, and at higher concentrations of the acid the oxygen is mainly protonated with a positive partial charge -O + -H, accelerating the redox reactions
References
- askIITians. ((2006-2018)). askIITians. Retrieved on March 29, 2018, from askIITians: askiitians.com
- Encyclopaedia Britannica, Inc. (2018). Encyclopaedia Britannica. Retrieved on March 29, 2018, from Encyclopaedia Britannica: britannica.com
- Tox Town. (2017). Tox Town. Retrieved on March 29, 2018, from Tox Town: toxtown.nlm.nih.gov
- Professor Patricia Shapley. (2010). Nitrogen Oxides in the Atmosphere. University of Illinois. Retrieved on March 29, 2018, from: butane.chem.uiuc.edu
- Shiver & Atkins. (2008). Inorganic chemistry. In The elements of group 15. (fourth ed., Pp. 361-366). Mc Graw Hill