Nitrogen is the lightest element in Periodic Table Group 15, also known as the pnictogens. Dinitrogen, a colourless and odourless diatomic gas with the formula N2, is formed when two atoms of the element join together at STP.
Dinitrogen is the most abundant uncombined element, accounting for around 78% of the Earth’s atmosphere. Nitrogen is found in all living things, most notably in amino acids, nucleic acids (DNA and RNA), and adenosine triphosphate, an energy transfer molecule.
The human body contains approximately 3% nitrogen by mass. The nitrogen cycle describes the movement of nitrogen from the atmosphere to the biosphere and organic compounds, and then back to the atmosphere.
Dinitrogen
Dinitrogen constitutes 78% of the earth’s atmosphere, making it the most abundant element in the atmosphere and the seventh most abundant uncombined element in the universe. Daniel Rutherford, a Scottish physician, discovered this element for the first time in 1772. This chemical element’s symbol is N, and its atomic number is 7.
Preparation
Dinitrogen is commercially produced by liquefaction and fractional distillation of air. Liquid dinitrogen separates first, leaving liquid oxygen behind. Dinitrogen is synthesized in the laboratory by reacting an aqueous solution of ammonium chloride with sodium nitrite.
NH4CI(aq) + NaNO2 (aq) → N2 (g) + 2H2O(l) + NaCl (aq)
In this reaction, small amounts of NO and HNO3 are formed; these impurities can be removed by passing the gas through aqueous sulphuric acid containing potassium dichromate. It can also be made by thermally decomposing ammonium dichromate.
(NH4)2Cr2O7 → N2 + 4H2O + Cr2O3
The thermal decomposition of sodium or barium azide can yield very pure nitrogen.
Ba(N3)2 → Ba + 3N2
Properties of Dinitrogen
- Dinitrogen is a non-toxic gas that is colourless, odourless, and tasteless.
- The atom of nitrogen has two stable isotopes.
- It has very low water solubility and low freezing and boiling points.
- Because of the high bond enthalpy of the N≡N bond, dinitrogen is relatively inert at room temperature.
- Reactivity, on the other hand, increases rapidly as the temperature rises. At higher temperatures, it directly combines with some metals to form predominantly ionic nitrides and covalent nitrides with nonmetals.
- Nitrogen condenses to form a colourless liquid, which solidifies to form a snow-like mass.
- At room temperature, N2 is almost non-reactive. It does not burn and does not support combustion. The chemical inertness of N2 at room temperature is due to the molecule’s high stability.
- It has been known to react with metals such as lithium, alkali metals, and calcium under very mild conditions. Such reactions are known to be surface tarnishing reactions, with the final bulk product being a metal nitride, such as Li3N.
Reactions with Dinitrogen
- Combination with Electropositive Metals
At high temperatures, it combines with some highly electropositive metals to form nitrides. At low temperatures, lithium nitride forms slowly, but quickly at high temperatures. Magnesium and aluminium continue to burn in a nitrogen atmosphere, forming nitrides. When calcium, strontium, and barium are red hot, they react with N2.
6Li+N2 → 2Li3N2
3Mg+N2 → Mg3N2
2Al+N2 → 2AlN
3Ca+N2 → Ca3N2
- Combination with O2
In the presence of an electric arc (above 3273K), N2 combines with O2 to form nitric oxide.
N2 +O2 → 2NO
Uses of Dinitrogen
- Dinitrogen is primarily used in the production of ammonia and other nitrogen-containing industrial chemicals (e.g., calcium cyanamide).
- It is also used in situations where an inert atmosphere is required (e.g., in the iron and steel industry, inert diluent for reactive chemicals).
- Liquid dinitrogen is a refrigerant that is used to preserve biological materials, food, and cryosurgery.
Nitrogen Cycle
The nitrogen cycle is the movement of nitrogen in various forms throughout nature. Nitrogen is required for life on Earth because it is a component of proteins and nucleic acids. Although nitrogen gas constitutes 78% of the atmosphere by volume, this abundant reservoir exists in an unusable form for most organisms.
- Nitrogen is made available to plants through a series of microbial transformations, which in turn sustain all animal life. Nitrogen fixation, nitrogen assimilation, ammonification, nitrification, and denitrification are the classifications for the steps, which are not all sequential.
- Nitrogen fixation, or the conversion of nitrogen gas into inorganic nitrogen compounds, is primarily accomplished by certain bacteria and blue-green algae. A much smaller amount of free nitrogen is fixed abiotically and through the Haber-Bosch process, which converts it to ammonia.
- Nitrogen fixation produces nitrates and ammonia, which are incorporated into algae and higher plants’ specialized tissue components. These algae and plants are then consumed by animals, where they are converted into their own body compounds.
- Microorganisms decompose the remains of all living things and their waste products in the ammonification process, which produces ammonia and ammonium. Foul-smelling putrefactive products may appear under anaerobic, or oxygen-free, conditions, but they, too, are converted to ammonia over time. Depending on soil conditions, ammonia can either leave the soil or be converted into other nitrogen compounds.
- Nitrification is the process by which nitrifying bacteria convert soil ammonia into nitrates (NO3–) that plants can incorporate into their own tissues.
Sample Questions
Question 1: Give some uses of dinitrogen.
Answer:
It is primarily used in the industrial production of compounds such as ammonia, calcium cyanamide, and others. Dinitrogen is used to create an inert atmosphere in industries such as iron and steel. In the food industry, liquid nitrogen is used as a preservative as well as a refrigerant.
Question 2: Why does nitrogen exhibits a +5 oxidation state, but not form pentahalide?
Answer:
Nitrogen has only s and p orbitals when n = 2. It lacks d orbitals, which would allow it to expand its covalence beyond four. As a result, it does not form pentahalide.
Question 3: Why does NO2 dimerize?
Answer:
NO2 has an even number of valence electrons. It behaves like any other odd molecule. Dimerization converts it to a stable N2O4 molecule with an even number of electrons.
Question 4: What are the major acids which are formed by Nitrogen?
Answer:
Nitrogen produces oxoacids such as H2N2O2 (hyponitrous acid), HNO2 (nitrous acid), and HNO3 (hydrogen peroxide) (nitric acid).
Question 5: How is dinitrogen produced commercially?
Answer:
Dinitrogen is commercially produced by liquefaction and fractional distillation of air. Liquid dinitrogen separates first, leaving liquid oxygen behind. In the lab, dinitrogen is made by mixing an aqueous solution of ammonium chloride with sodium nitrite.