• Nitrogen is a?diatomic?molecule and the main?unreactive gas?in air
• 78% of air is nitrogen gas
• The lack of reactivity of nitrogen gas can be explained by looking at its?intramolecular bonds
• Intramolecular bonds are the bonds?within?a molecule

Bonding in nitrogen

• The electron configuration of a nitrogen atom is 1s²?2s²?2p³
• To achieve a full outer shell of electrons, it needs to gain three electrons
• Nitrogen atoms therefore form a?triple covalent bond?between two nitrogen atoms in which they?share?three electrons with each other

The diagram shows a triple covalent bond between two nitrogen atoms to achieve a full outer shell of electrons

• The?bond enthalpy?of the nitrogen triple bond is 1000 kJ mol^-1
• This means that 1000 kJ of energy is needed to break one mole of N₂?triple bond
• As it is so difficult to break the nitrogen triple bond, nitrogen and oxygen gas in air will not react with each other
• Only under extreme conditions will nitrogen gas react (eg. during a thunderstorm)

Polarity of nitrogen

• The electrons in a nitrogen molecule are shared?equally?between the two nitrogen atoms
• Therefore, nitrogen molecules are?nonpolar?molecules

Since the electronegativity of the two nitrogen atoms is the same, the will pull the electrons towards them equally so overall the molecule is nonpolar

• Due to the lack of polarity, nitrogen gas is?not attracted to?or?likely to react with?other molecules the way polar molecules would

• Ammonia?is a compound of nitrogen and will turn damp?red?litmus paper?blue?as it is an?alkaline?gas
• Ammonia is made on a large scale in industry using the?Haber?process:

N₂(g) + 3H₂(g) ? 2NH₃(g)

Basicity of ammonia

• Ammonia can act as a?Br?nsted–Lowry base?by accepting a?proton?(H+) using the?lone?pair?of electrons on the nitrogen atom to form an?ammonium ion:

NH₃(aq) + H⁺(aq) →? NH₄⁺(aq)

• In an aqueous solution of ammonia, an equilibrium mixture is established

NH₃(aq) + H₂O(l) ?? NH₄⁺(aq) + OH^-(aq)

• Since the position of the equilibrium lies well over to the left the ammonia solution is only?weakly alkaline
• There is a higher concentration of ammonia molecules than hydroxide ions in solution
• Ammonia is therefore a?weak base

Structure & formation of ammonium ion

• The ammonium ion is formed by an acid-base reaction of ammonia with water:

NH₃(aq) + H₂O(l) ?? NH₄⁺(aq) + OH^-(aq)

• The nitrogen in ammonia is covalently bonded to three hydrogen atoms and has one lone pair of electrons causing the ammonia molecule to have a?pyramidal shape

Ammonia has a pyramidal shape due to its lone pair of electrons

• The nitrogen atom in ammonia uses its lone pair of electrons to form a dative bond with a proton to form the ammonium ion
• The ammonium ion has a?tetrahedral shape?in which all bonds have the same?length

The tetrahedral shape of the ammonium ion

Preparation of ammonia gas from an ammonium salt

• Ammonia gas can be prepared from an ammonium salt and a base in an acid-base reaction:

• Ammonium chloride (NH₄Cl) and calcium hydroxide (Ca(OH)₂) are mixed together and then heated
• NH₄⁺acts as an?acid?(proton donor) and OH^-?acts as a?base?(proton acceptor)
• This acid-base reaction can be used to test if an?unknown solution?contains ammonium ions
• If the unknown solution does contain ammonium ions, it will react with calcium hydroxide to form ammonia gas
• This ammonia gas will turn damp red litmus paper blue

The diagram shows the apparatus set up for the preparation of ammonia gas from an ammonium salt and calcium hydroxide