nitrogen and sulfur

• Nitrogen is a diatomic molecule and the main unreactive gas in air, making up 78% of air.
• The lack of reactivity of nitrogen gas can be explained by looking at its intramolecular bonds.
• Intramolecular bonds are the bonds within a molecule.
• The electron configuration of a nitrogen atom is 1s2, 2s2, 2p.
• To achieve a full outer shell of electrons, a nitrogen atom needs to gain three electrons.
• Nitrogen atoms form a triple covalent bond between two nitrogen atoms in which they share three electrons with each other.
• The bond enthalpy of the nitrogen triple bond is 1000 kJ mol, meaning that 1000 kJ of energy is needed to break one mole of N triple bond.
• Nitrogen gas is very difficult to break the nitrogen triple bond, hence nitrogen and oxygen gas in air will not react with each other.
• The electrons in a nitrogen molecule are shared equally between the two nitrogen atoms, making nitrogen molecules nonpolar molecules.
• Due to the lack of polarity, nitrogen gas is not attracted to or likely to react with other molecules the way polar molecules would.
• Since the position of the equilibrium lies well over to the left the ammonia solution is only weakly alkaline.
• The ammonium ion is formed by an acid-base reaction of ammonia with water: NH (aq) + H O(l) ⇌ NH (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.
• The apparatus set up for the preparation of ammonia gas from an ammonium salt and calcium hydroxide is shown in the diagram.
• Ammonia is made on a large scale in industry using the Haber process: N (g) + 3H (g) ⇌ 2NH (g).
• Ammonia can act as a Brønsted–Lowry base by accepting a proton (H) using the lone pair of electrons on the nitrogen atom to form an ammonium ion: NH (aq) + H (aq) ⇌ NH (aq) + OH (aq).
• Ammonia is a compound of nitrogen and will turn damp red litmus paper blue as it is an alkaline gas.
• Ammonia gas can be prepared from an ammonium salt and a base in an acid-base reaction: Ammonium chloride (NH Cl) and calcium hydroxide (Ca(OH) ) are mixed together and then heated.
• This acid-base reaction can be used to test if an unknown solution contains ammonium ions.
• There is a higher concentration of ammonia molecules than hydroxide ions in solution Ammonia is therefore a weak base.
• 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.
• If the unknown solution does contain ammonium ions, it will react with calcium hydroxide to form ammonia gas.
• The ammonia gas will turn damp red litmus paper blue.
• The ammonium ion has a tetrahedral shape in which all bonds have the same length.
• NH acts as an acid (proton donor) and OH acts as a base (proton acceptor) in this acid-base reaction.
• In an aqueous solution of ammonia, an equilibrium mixture is established: NH (aq) + H O(l) ⇌ NH (aq) + OH (aq).
• Sulfur(IV) oxide (SO ) is another pollutant found in the atmosphere.
• When the clouds rise, the temperature decreases, and the droplets get larger.
• When SO is oxidised, it forms SO which reacts with rainwater to form dilute sulfuric acid as follows: 2SO (g) + H O(l) → H SO (aq).
• The nitrogen(IV) oxide (NO ) dissolves and reacts in water with oxygen as follows: NO (aq) + H O(l) + 1½O (g) → 2HNO (aq).
• The formed NO gets oxidised to regenerate NO: NO(g) + ½ O (g) → NO (g).
• Acid rain also contains dilute sulfuric acid (H SO ).
• The air also contains oxygen and tiny droplets of water that make up clouds.
• Nitrogen oxides can directly cause acid rain but can also act as catalysts in the formation of acid rain.
• The formation of dilute sulfuric acid is catalysed by the nitrogen oxides.
• The regenerated NO molecule can get again oxidise another SO molecule to SO which will react with rainwater to form H SO.
• When the droplet containing dilute nitric acid are heavy enough, they will fall down as acid rain.
• NO catalyses the oxidation of SO to SO: NO (g) + SO (g) → SO (g) + NO(g).
• Lightning strikes trigger the formation of nitrogen(II) and nitrogen (IV) oxides in air: 2NO(g) + O (g) ⇌ 2NO (g).