3m. The covalent bonding in the nitrogen molecule N₂

Below is a further selection of dot & cross electronic Lewis diagrams for covalent bonding in molecules, particularly simple organic molecules.

Only the outer valency electrons are shown for carbon, nitrogen, oxygen and chlorine.

Can you deduce these electronic diagrams of covalently bonded molecules for yourself?

Ex. 10 nitrogen N₂; Ex. 11 ethane C₂H₆;

Ex. 12 chloromethane CH₃Cl and Ex. 13 methanol CH₃OH.

Electronic origin of the diagrams showing the outer electrons of N, C, Cl and O: N at. no. 7 (2.5), H at. no. (1), C at. no. 6 (2.4), Cl at. no. 17 (2.8.7) and O at. no. 8 (2.6) plus a variety of crosses and blobs!

The valencies or combining power in these examples are N 3, H 1, C 4, Cl 1 and O 2, so,  these valency numbers correspond to the number of electrons the atom needs to give a stable outer shell - that's what valency is all about!

Only the outer electrons are shown in the dot and cross Lewis diagram of nitrogen below.

Extra notes on Nitrogen (N₂) for e.g. GCSE/IGCSE Level Chemistry Revision Notes

Properties

• Formula: N₂
• Molecular form: Diatomic molecule with a triple covalent bond (very strong, inert).
• Physical properties:
  • Colourless, odourless gas
  • Slightly less dense than air
  • Insoluble in water
• Chemical properties:
  • Very unreactive at room temperature (due to strong triple bond)
  • Reacts at high temperature/pressure with hydrogen → ammonia (Haber process)
  • Reacts with oxygen at high temperatures → nitrogen oxides (NO, NO₂)

Industrial Manufacture

• Fractional distillation of liquid air:
  • Air cooled and liquefied
  • Nitrogen separated (boiling point −196 °C)
• Haber process (indirect relevance):
  • Nitrogen + hydrogen → ammonia
    N₂ + 3H₂ ==> 2NH₃ (iron catalyst, 450 °C, 200 atm)

Uses of Nitrogen

• Industrial:
  • Manufacture of ammonia (Haber process → fertilizers, nitric acid)
  • Manufacture of nitric acid (Ostwald process)
• Food industry:
  • Preserving packaged food (inert atmosphere)
• Medical:
  • Liquid nitrogen for cryogenics, preservation
• Everyday life:
  • Inert atmosphere in welding, electronics
  • Used in light bulbs (to prevent filament oxidation)

Typical Exam Board Requirements

Student Exam Tips

• Always state N₂, not N, for nitrogen gas.
• Triple bond: Mention strong triple bond → explains inertness.
• Industrial manufacture: Fractional distillation of liquid air is the main method.
• Uses: Link to fertilizers (Haber process), food preservation, cryogenics.
• Environmental context: Nitrogen oxides → acid rain, photochemical smog.
• Exam wording: Nitrogen is inert at room temperature but reactive under extreme conditions.

Common Misconceptions

• Thinking nitrogen is reactive at room temperature (it is inert due to strong triple bond).
• Forgetting nitrogen is diatomic (N₂, not N).
• Assuming nitrogen is the main component of oxygen (air is ~78% nitrogen, ~21% oxygen).
• Believing nitrogen directly forms fertilizers (it must first be converted to ammonia/nitrates).
• Confusing nitrogen oxides with nitric acid (NO/NO₂ are gases, HNO₃ is an acid).