Properties

• Dinitrogen is a colourless, odourless, tasteless and non-toxic gas.

• It has two stable isotopes: 14N and 15N.• It has a very low solubility in water and low freezing and boiling points .

• Dinitrogen is rather inert at room temperature because of the high bond enthalpy of N≡N bond.

• At higher temperatures, it directly combines with• some metals to form predominantly ionic nitrides

and with non-metals,covalent nitrides. 6Li + N2 Heat → 2Li3N 3Mg + N2 Heat → Mg3N2

Reactivity towards hydrogen

• It combines with hydrogen at about 773 K in the presence of a catalyst (Haber’s Process) to form ammonia:

N2(g) + 3H2(g) → 2NH3(g);

AMMONIA

NH2 CONH2 + 2H2 O →( NH4)2 CO3 →2NH3 + H2 O + CO2

2NH4Cl + Ca(OH)2 → 2NH3 + 2H2O +CaCl2(NH4)2 SO4 + 2NaOH → 2NH3 + 2H2O +

Na2SO4

Haber’s process

• N2(g) + 3H2(g) →2NH3(g); Δf H0 – 46.1 kJ mol–1

• The optimum conditions a pressure of 200 × 105 Pa (about 200 atm), a temperature of ~ 700 K and the use of a catalyst such as ironoxide

with small amounts of K2O and Al2O3 to increase the rate of attainment of equilibrium

Flow chart diagram

PROPERTIES OF AMMONIA

• colourless gas with a pungent odour• freezing and boiling points are 198.4 and

239.7 K respectively. • In the solid and liquid states, it is associated

through hydrogen bonds and that accounts for its higher melting and boiling points

Hydrogen Bonding in Ammonia

Ammonia gas is highly soluble in water

Structure of ammonia

• ammonia molecule is trigonal pyramidal with the nitrogen atom at the apex.

• It forms ammonium salts with acids, e.g., NH4Cl, (NH4)2 SO4, etc.

• As a weak base, it precipitates the hydroxides of many metals from their salt solutions.

2FeCl3 +NH4 OH aq→ Fe2 O 3. xH 2O + 3NH4Cl

LEWIS BASE

• The presence of a lone pair of electrons on the nitrogen atom of the ammonia molecule makes it a Lewis base.

It donates the electron pair and forms linkage with metal ions and the formation of such complex compounds finds applications in detection of metal ions

such as Cu2+, Ag+:• Cu2+ (aq) + 4 NH3(aq) → [Cu(NH3)4]2+ (aq)

• Ag + (aq) +Cl − (aq) →AgCl (s)white ppt)

Uses Of Ammonia

• Ammonia is used to produce various nitrogenous fertilisers (ammonium nitrate, urea, ammonium phosphate and ammonium sulphate)

• and in the manufacture of some inorganic nitrogen compounds like nitric acid. Liquid ammonia is also used as a refrigerant

Oxides of Nitrogen

• Nitrogen forms a number of oxides in different oxidation states

(1) Dinitrogen oxide [Nitrogen(I) oxide] NH4NO3→ N2O +2H2O

colourless gas, neutral

(2) Nitrogen monoxide NO [Nitrogen(II) oxide]

• 2NaNO2 + 2FeSO 4+ 3H 2SO4 → Fe 3(SO4)3 + 2NaHSO4 + 2H2 O + 2NO

colourless gas , neutral

Dinitrogen trioxide N2O3 [Nitrogen(III) oxide

• 2NO + N2O → 2N2 O3

blue solid

Nitrogen dioxide NO2 [Nitrogen(IV) oxide]

673 K 2Pb(NO3)2 → 4NO2 +PbO

brown gas, acidic

Dinitrogen tetroxide [Nitrogen(IV) oxide]

N2O4

COOL

2NO2 → N2O4 HEAT

colourless solid/ liquid, acidic

Dinitrogen pentoxide N2O5 Nitrogen(V) oxide]

• 4HNO3+ P4 O10 →4HPO3 + 2N2 O5

colourless solid, acidic

Lewis structure of NO2

LEWIS STRUCTURE OF N2O

LEWIS STRUCYURE OF NO

LEWIS STRUCTURE OF N2O5

LEWIS STRUCTURE OF N2O3

OXOACIDS OF NITROGEN

• Nitrogen forms oxoacids such as H2N2O2 (hyponitrous acid), HNO2 (nitrous acid) and HNO3 (nitric acid). Amongst them HNO3 is the most important

NITRIC ACID

• PREPARATION - LAB

• NaNO3 + H2 SO 4→ NaHSO4 + HNO3

MANUFACTURE

• On a large scale it is prepared by Ostwald’s process.• This method is based upon catalytic oxidation of NH3 by

atmospheric oxygen. Pt /Rh gauge catalyst 500K, 9 bar 2 4NH3( )g + 5 O 2(g) → 4NO( g) + 6H2 O (g)⎯⎯⎯⎯⎯⎯⎯⎯ (from air)• Nitric oxide thus formed combines with oxygen giving NO2. 2NO g +O 2g → 2NO 2g Nitrogen dioxide so formed, dissolves in water to give HN 3NO 2g + H2 O (l) →2HNO3(aq) + NO(g)

STRUCTURE OF NITRIC ACID• In the gaseous state, HNO3 exists as a planar

molecule

Uses of nitric acid

• The major use of nitric acid • in the manufacture of ammonium nitratefor

fertilisers and other nitrates for use in explosives and pyrotechnics.

used for the preparation of nitroglycerin, trinitrotoluene and other organic nitro compounds.

Other major uses are in the pickling of stainless steel,etching of metals and as an oxidiser in rocket fuels

PHOSPHORUS

• Phosphorus is found in many allotropic forms, the important ones being white, red and black.

• White phosphorus is a translucent white waxy solid. It is poisonous, insoluble in water but soluble in carbon disulphide and glows in dark

(chemiluminescence). It dissolves in boiling NaOH solution in an inert

atmosphere giving PH3. P 4+ 3NaOH + 3H 2O → PH 3+ 3NaH2 PO2

WHITE P

• White phosphorus is less stable and therefore, more reactive and readily catches fire.

• because of angular strain in the P4 molecule where the angles are only 60°

Red phosphorus

obtained by heating white phosphorus at 573K in an inert atmosphere for several days.• red phosphorus is much less reactive than

white phosphorus because It is polymeric, consisting of chains of P4 tetrahedra linked together . It does not glow in the dark