Nitrogen Chemistry

• Nitrogen is at the top of group 5 in the periodic table and therefore has 5 electrons in its outer shell.

• Nitrogen naturally occurs as a diatomic molecule, N₂, forming a triple bond.

• Triple bonds are very difficult to break so N₂is very unreactive.

Ammonia and ammonium ions

• Ammonia, NH₃, is formed from the reaction between N₂ and H₂

• Ammonia is polar and and can form hydrogen bonds, so is soluble in water

• The lone pair allows ammonia to form dative covalent bonds.

  • Ammonia can act as a ligand and form complex ions with transition metals

  • Ammonia can act as a base and accept protons to form ammonium ions

    • NH₃ + H⁺ ⇋ NH₄⁺

• Ammonium ions can be tested for by gently heating with sodium hydroxide

  • NH₄⁺_(aq) + OH^-_(aq) → NH_3(g) + H₂O_(l)

  • Ammonia gas is alkaline so damp red litmus paper will turn blue if ammonia gas is produced

Nitrogen oxides

• NO

  • Nitrogen monoxide, nitric oxide, nitrogen (II) oxide.

  • A colourless gas

• N₂O

  • Dinitrogen monoxide, nitrous oxide, nitrogen (I) oxide (laughing gas)

  • Colourless, sweet smelling gas

• NO₂

  • Nitrogen dioxide, nitrogen (IV) oxide

  • Brown, toxic gas with a sharp odour

Nitrates

• Nitrate (V) ions have the formula NO₃^-

• To test for nitrate (V) ions, heat with sodium hydroxide and aluminium foil / devarda’a alloy

• Aluminium reduces nitrate ions to ammonia

  • 3NO_3(aq) + 8Al_(s) + 5OH^-_(aq) + 18H₂O_(l) → 3NH_3(g) + 8[Al(OH)₄]^-_(aq)

Nitrogen cycle

• N₂ + 3H₂ → 2NH₃

• NH₃ + H⁺ → NH₄⁺

• NH₄⁺ + O₂ → NO₂^- + 4H⁺ + 2e^-

• NO₂^- + H₂O → NO₃^- + 2H⁺ + 2e^-

• 2NO₃^- + 12H⁺ + 10e^- → N₂ + 6H₂O

• Producing nitrogen oxides

  • N₂ + O₂ → 2NO

  • N₂ + 2O₂ → 2NO₂

  • 2N₂ + O₂ → 2N₂O