1 Properties Dinitrogen is a colourless, odourless, tasteless and non-toxic gas. It has two stable isotopes: 14 N and 15 N. It has a very low solubility in water and low freezing and boiling points.

2 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

3 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);

4 AMMONIA NH 2 CONH 2 + 2H 2 O →( NH 4 ) 2 CO 3 →2NH 3 + H 2 O + CO 2 2NH 4 Cl + Ca(OH) 2 → 2NH 3 + 2H 2 O +CaCl 2 (NH 4 ) 2 SO 4 + 2NaOH → 2NH 3 + 2H 2 O + Na 2 SO 4

5 Haber’s process f N 2 (g) + 3H 2 (g) →2NH 3 (g); Δ f H 0 – 46.1 kJ mol –1 The optimum conditions a pressure of 200 × 10 5 Pa (about 200 atm), a temperature of ~ 700 K and the use of a catalyst such as ironoxide with small amounts of K 2 O and Al 2 O 3 to increase the rate of attainment of equilibrium

6 Flow chart diagram

7 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

8 Hydrogen Bonding in Ammonia

9 Ammonia gas is highly soluble in water

10 Structure of ammonia ammonia molecule is trigonal pyramidal with the nitrogen atom at the apex.

11 It forms ammonium salts with acids, e.g., NH 4 Cl, (NH 4 ) 2 SO 4, etc. As a weak base, it precipitates the hydroxides of many metals from their salt solutions. 2FeCl 3 +NH 4 OH aq→ Fe 2 O 3. xH 2 O + 3NH 4 Cl

12 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)

13 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

14 Oxides of Nitrogen Nitrogen forms a number of oxides in different oxidation states (1) Dinitrogen oxide [Nitrogen(I) oxide] NH 4 NO 3 → N 2 O +2H 2 O colourless gas, neutral

15 (2) Nitrogen monoxide NO [Nitrogen(II) oxide] 2NaNO 2 + 2FeSO 4 + 3H 2 SO 4 → Fe 3 (SO 4 ) 3 + 2NaHSO 4 + 2H 2 O + 2NO colourless gas, neutral

16 Dinitrogen trioxide N 2 O 3 [Nitrogen(III) oxide 2NO + N 2 O → 2N 2 O 3 blue solid

17 Nitrogen dioxide NO 2 [Nitrogen(IV) oxide] 673 K 2Pb(NO3) 2 → 4NO 2 +PbO brown gas, acidic

18 Dinitrogen tetroxide [Nitrogen(IV) oxide] N 2 O 4 COOL 2NO2 → N2O4 HEAT colourless solid/ liquid, acidic

19 Dinitrogen pentoxide N2O5 Nitrogen(V) oxide] 4HNO 3 + P 4 O 10 →4HPO 3 + 2N 2 O 5 colourless solid, acidic

20 Lewis structure of NO2

21 LEWIS STRUCTURE OF N2O

22 LEWIS STRUCYURE OF NO

23 LEWIS STRUCTURE OF N2O5

24 LEWIS STRUCTURE OF N2O3

25 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

26 NITRIC ACID PREPARATION - LAB NaNO3 + H2 SO 4→ NaHSO4 + HNO3

27 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)

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

29 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

30 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

31 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°

32 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