The valences of nitrogen ranging from -3 as ammonia and amines, to the +5 and nitric acid (Tyagi, 2009). This element does not expand valences like others.
The nitrogen atom is a chemical element with atomic number 7 and the first element of group 15 (formerly VA) of the periodic table. The group consists of nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), and moscovium (Mc).
Figure 1: Bohr diagram of the nitrogen atom.
The elements share certain general similarities in chemical behavior, although they are clearly differentiated from each other chemically. These similarities reflect common characteristics of the electronic structures of their atoms (Sanderson, 2016).
Nitrogen is present in almost all proteins and plays an important role in both biochemical and industrial applications. Nitrogen forms strong bonds due to its ability to triple bond with another nitrogen atom and other elements.
Therefore, there is a large amount of energy in nitrogen compounds. Before 100 years ago, little was known about nitrogen. Now, nitrogen is commonly used to preserve food, and as a fertilizer (Wandell, 2016).
Electronic configuration and valences
In an atom, electrons fill the different levels according to their energies. The first electrons fill the lower energy levels and then move to a higher energy level.
The outermost energy level in an atom is known as the valence shell and the electrons placed in this shell are known as valence electrons.
These electrons are mainly found in bond formation and chemical reaction with other atoms. Therefore, valence electrons are responsible for different chemical and physical properties of an element (Valence Electrons, SF).
Nitrogen, as mentioned before, has an atomic number of Z = 7. This implies that its filling of electrons in their energy levels, or electron configuration, is 1S 2 2S 2 2P 3.
It must be remembered that in nature, atoms always seek to have the electronic configuration of noble gases, either by gaining, losing or sharing electrons.
In the case of nitrogen, the noble gas that seeks to have an electronic configuration is neon, whose atomic number is Z = 10 (1S 2 2S 2 2P 6) and helium, whose atomic number is Z = 2 (1S 2) (Reusch, 2013).
The different ways nitrogen has of combining will give it its valence (or oxidation state). In the specific case of nitrogen, because it is in the second period of the periodic table, it is unable to expand its valence layer as the other elements in its group do.
It is expected to have valences of -3, +3, and +5. However, nitrogen has valence states ranging from -3, as in ammonia and amines, to +5, as in nitric acid. (Tyagi, 2009).
The valence bond theory helps to explain the formation of compounds, according to the electron configuration of nitrogen for a given oxidation state. For this, it is necessary to take into account the number of electrons in the valence shell and how much is left to acquire a noble gas configuration.
Nitrogen compounds
Figure 2: structure of molecular nitrogen with valence 0.
Given its large number of oxidation states, nitrogen can form a large number of compounds. In the first instance, it must be remembered that in the case of molecular nitrogen, by definition its valence is 0.
The oxidation state of -3 is one of the most common for the element. Examples of compounds with this oxidation state are ammonia (NH3), amines (R3N), ammonium ion (NH 4 +), imines (C = NR) and nitriles (C≡N).
In the oxidation state -2, nitrogen is left with 7 electrons in its valence shell. This odd number of electrons in the valence shell explains why compounds with this oxidation state have a bridge bond between two nitrogen. Examples of compounds with this oxidation state are hydrazines (R 2 -NNR 2) and hydrazones (C = NNR 2).
In the -1 oxidation state, nitrogen is left with 6 electrons in the valence shell. Examples of nitrogen compounds with this valence are hydroxyl amine (R 2 NOH) and azo compounds (RN = NR).
In positive oxidation states, nitrogen is generally attached to oxygen atoms to form oxides, oxysalts, or oxacids. In the case of the +1 oxidation state, nitrogen has 4 electrons in its valence shell.
Examples of compounds with this valence are dinitrogen oxide or laughing gas (N 2 O) and nitroso compounds (R = NO) (Reusch, Oxidation States of Nitrogen, 2015).
For the case of the oxidation state of +2, an example is nitrogen oxide or nitric oxide (NO), a colorless gas produced by the reaction of metals with dilute nitric acid. This compound is an extremely unstable free radical since it reacts with O 2 in air to form NO 2 gas.
Nitrite (NO 2 -) in basic solution and nitrous acid (HNO 2) in acid solution are examples of compounds with oxidation state +3. These can be oxidizing agents to normally produce NO (g) or reducing agents to form the nitrate ion.
Dinitrogen trioxide (N 2 O 3) and the nitro group (R-NO 2) are other examples of nitrogenous compounds with valence +3.
Nitric dioxide (NO 2) or nitrogen dioxide is a nitrogen compound with valence +4. It is a brown gas generally produced by the reaction of concentrated nitric acid with many metals. Dimerizes to form N 2 O 4.
In state +5 we find nitrates and nitric acid which are oxidizing agents in acid solutions. In this case, nitrogen has 2 electrons in the valence shell, which are in the 2S orbital. (Oxidation states of nitrogen, SF).
There are also compounds such as nitrosilazide and dinitrogen trioxide where nitrogen has various oxidation states in the molecule. In the case of nitrosilazide (N 4 O), nitrogen has a valence of -1, 0, + 1 and +2; and in the case of dinitrogen trioxide, it has a valence of +2 and +4.
Nomenclature of nitrogen compounds
Given the complexity of the chemistry of nitrogen compounds, the traditional nomenclature was not enough to name them, much less identify them properly. That is why, among other reasons, that the International Union of Pure and Applied Chemistry (IUPAC) created a systematic nomenclature where compounds are named according to the number of atoms they contain.
This is beneficial when it comes to naming nitrogen oxides. For example nitric oxide would be named nitrogen monoxide and nitrous oxide (NO) dinitrogen monoxide (N 2 O).
Additionally, in 1919, the German chemist Alfred Stock developed a method for naming chemical compounds based on the oxidation state, which is written in Roman numerals enclosed in parentheses. Thus, for example, nitric oxide and nitrous oxide would be called nitrogen oxide (II) and nitrogen oxide (I) respectively (IUPAC, 2005).
References
- (2005). NOMENCLATURE OF INORGANIC CHEMISTRY IUPAC Recommendations 2005. Retrieved from iupac.org.
- Oxidation states of nitrogen. (SF). Recovered from kpu.ca.
- Reusch, W. (2013, May 5). Electron Configurations in the Periodic Table. Recovered from chemistry.msu.edu.
- Reusch, W. (2015, August 8). Oxidation States of Nitrogen. Recovered from chem.libretexts.org.
- Sanderson, RT (2016, December 12). Nitrogen group element. Recovered from britannica.com.
- Tyagi, VP (2009). Essential Chemistry Xii. New Deli: Ratna Sagar.
- Valence Electrons. (SF). Recovered from chemistry.tutorvista.com.
- Wandell, A. (2016, December 13). Chemistry of Nitrogen. Recovered from chem.libretexts.org.