Dinitrogen

Dinitrogen (N₂) is a chemical molecule formed when two nitrogen atoms create a covalent bond. This pure nitrogen gas is colourless and odourless and comprises about 78% of the Earth's atmosphere. Dinitrogen is the most stable form of nitrogen, known as molecular nitrogen or nitrogen gas. In this form, two nitrogen atoms are connected by a triple covalent bond, which fulfils the Lewis electron rules. The lone non-bonding electron pairs on each nitrogen atom are at a low energy level.

1.0Introduction

Dinitrogen is the most prevalent uncombined element, making up approximately 78% of Earth's atmosphere. It is a crucial component of all living organisms, prominently featured in amino acids, nucleic acids (DNA and RNA), and adenosine triphosphate (ATP), which are vital for energy transfer. This element was first discovered by Scottish physician Daniel Rutherford in 1772. Its chemical symbol is N, and its atomic number is 7.

2.0Preparation of Dinitrogen (N₂​)

1. Laboratory Method of Preparation of Dinitrogen (N₂​)

• In the laboratory, dinitrogen is prepared by heating a solution of ammonium chloride and sodium nitrite.

NH₄Cl(aq) + NaNO₂(aq) → NaCl(aq) + 2H₂O(l) + N₂(g)

• This reaction also forms small amounts of nitric oxide and nitric acid. The N_2​ thus obtained is purified by passing the evolved gas through an aqueous sulfuric acid solution containing potassium dichromate.

2. Other Methods of Preparation of N₂

• By Thermal Decomposition of Ammonium Dichromate: When red crystals of ammonium dichromate are heated, a violent reaction takes place, accompanied by flashes of light and the evolution of nitrogen:

(NH₄)₂Cr₂O₇ → N₂ + 4H₂O + Cr2O₃

• By Oxidation of Ammonia: When ammonia is oxidised by red-hot copper oxide or by chlorine, nitrogen is obtained:

2NH₃ + 3CuO → N₂ + 3H₂O +3Cu₂8NH₃ + 3Cl₂  → N₂ + 6NH₄Cl

• By Thermal Decomposition of Sodium Azide: Pure nitrogen can be produced by heating sodium or barium azide.

2NaN₃→2Na+3N₂​Ba(N₃)₂→Ba+3N₂

Manufacturing of Dinitrogen (N₂​)

Commercially, N₂ is prepared by the fractional distillation of liquid air. Industrial nitrogen gas is produced through cryogenic fractional distillation of liquefied air, adsorption separation of the gaseous atmosphere, or membrane permeation. The cryogenic distillation method, developed in 1895, is the oldest technique for producing nitrogen.

3.0Fundamental Properties of Dinitrogen (Gaseous Dinitrogen)

• Appearance: Colorless and odourless.
• Magnetic Properties: Diamagnetic.
• Toxicity: Harmless gas.
• Solubility: Very slightly soluble in water.
• Physical States: Condenses to form a colourless liquid and solidifies to form a snow-like pile.

4.0Chemical Characteristics of Dinitrogen (Gaseous Dinitrogen)

• Bond Enthalpy: Due to the N≡N bond, dinitrogen has a high bond enthalpy, making it inert at ambient temperature. However, its reactivity increases with temperature.
• Reactivity with Metals: At elevated temperatures, nitrogen reacts with metals to form ionic nitrides.

           6Li + N₂ → 2Li₃N

• Haber’s Process: At around 773 K, dinitrogen combines with hydrogen to generate ammonia.

           N₂(g) +3H₂(g) ↔ 2NH₃(g)\

• Reactivity with Oxygen: At 2000 K, dinitrogen reacts with oxygen to form nitric oxide.

           N₂(g) + O₂(g) ↔ 2NO(g)

5.0Physical and Chemical Properties of Liquid Nitrogen

At atmospheric pressure, liquid nitrogen boils at 77 K (-196 °C, -321 °F). It is a cryogenic fluid capable of causing rapid freezing upon contact with living tissue, potentially leading to frostbite. Liquid nitrogen freezes at 63 K (-210 °C, -346 °F).

When properly insulated and placed away from surrounding heat, liquid nitrogen can be stored in vacuum flasks without significant loss. The very low temperature is maintained at 77 K by the slow boiling of the liquid, which releases nitrogen gas. Depending on the size and design, vacuum flasks can hold liquid nitrogen for a few hours to several weeks.

6.0Uses of Dinitrogen

• Industrial Applications of Nitrogen: Nitrogen is essential for producing ammonia and is used in explosives, fertilisers, and other materials. It also has diverse applications across various industries:
• Food Packaging: Nitrogen replaces oxygen in food packaging, extending the shelf life of perishables like vegetables, fruits, meats, and snacks. It also prevents damage during transportation. Liquid dinitrogen is a refrigerant for preserving biological materials, food items, and cryosurgery.
• Car tires: Nitrogen inflation improves tire performance and fuel economy by maintaining pressure longer than compressed air. It reduces corrosion risk and ensures consistent performance in various weather conditions, enhancing tire durability and driving experience.
• Chemical Blanketing: Nitrogen is used in explosive chemical plants to displace oxygen, preventing fires and explosions. By lowering oxygen levels, nitrogen creates a safer environment in factories, manufacturing facilities, and chemical plants.
• Electronics: In electronics assembly, nitrogen is used for soldering. It helps to combine components permanently by reducing surface tension and providing cleaner breaks from electric bonds. Nitrogen also prevents overheating in computers.
• Laboratory: Researchers and scientists use nitrogen to control oxygen levels, temperature, and humidity in laboratories, creating an ideal environment for sensitive procedures and tests. Nitrogen is also essential for purging lab equipment.
• Laser Cutting: Nitrogen is crucial in the steel industry for purging molten residue during laser cutting, resulting in stronger, corrosion-resistant stainless or aluminised steel products.