1. Chapter 16

2.  Nitrogen can complete its valence valence shell by:  1.) Electron gain: N 3- ion  This is found in saltlike nitrides.  2.) formation of electron pair bonds:  A) single bonds NH3  B) multiple bonds :N≡N: ; -N=N-, or NO 2  3.) formation of electron pair bonds with electron gain, NH 2 - or NH 2-  4.) Formation of electron pair bonds with electron loss (substituted ammonium ions)

3.  Three-Covalent Nitrogen  NR 3 molecules are sp 3 hybridised, the lone pair occupies the fourth position.  1.) all NR3 compounds behave as Lewis bases, give donor-acceptor complexes with lewis-acids, act as ligands towards transition metal ions [Co(NH 3 ) 6 ] 3+  2.) Pyramidal molecules (NRR’R’’) should be chiral. Optical isomers can not be isolated, because N oscillates through the plane of the R-groups. The energy barrier is only 24kJ/mol. (Inversion)

5.  3.) in few cases 3-covalent nitrogen is planar;  N-N single bond energy  The difference between C and N in bonding energies is attributable to the effects of repsulsion between nonbonding lone pairs. Nitrogen has little tendency to catenation.

6.  Nitrogens propensity to form p π - p π multiple bonds is a feature that distinguishes it from phosphorus and the other GroupVB elements.  N 2 has a high bond strength and a short internuclear distance (1.094Å). P forms infinite layer structures with only single bonds or P 4 molecules.  The oxo anions NO 2 - and NO 3 -, multiple bonds may be formulated in either resonance or MO terms.

7.  Nitrogen occurs as dinitrogen. N 2 (bp 77.3 K).  78% of the atmosphere is N 2  N 14 /N 15 has a ratio of 272.  N 15 compounds are used in tracer studies.  The NN triple bond is responsible for the inert behaviour of N 2.  N 2 is prepared by liquefaction and fractionation of air.

8.  N 2 only reacts with Li to give Li 3 N.  With certain transition metal complexes oand with nitrogen fixing bacteria.  Typical reactions of N 2 at elevated temperatures :

9.  Nitrides of eletropositives metals have structures with discrete nitrogen atoms and can be regarded as ionic (Ca 2+ ) 3 (N 3- ) 2  The Nitrides hydrolyse to ammonia and metal hydroxides.  Preparation:  Direct interaction  Loss of ammonia from amides on heating

10.  Transition metal nitrides are often nonstoichiometric and have nitrogen atoms in the interstices of close-packed arrays of metal atoms.  They are like the carbides or borides hard, chemically inert, high melting and electrically conducting.  Numerous covalent nitrides (BN,S 4 N 4,P 3 N 5 )  These nitrides have very differing properties, depending on the element.

11.  Ammonia is formed by the action of a base on an ammonium salt:  Industrially Ammonia is made by the haber- Bosch process at 400-500 deg C and 100- 1000atm.

12.  Ammonia is a colorless gas.  In liquid form it has a high heat of evaporation.  Liuid ammonia resembles water in its physical behaviour. It forms strong nydrogen bonds.  Its dielectric constant is around 22 at -34degC.  Liquid ammonia has lower reactivity towards electropositive metals and dissolves many of them.  AgI is insoluble in water but soluble in ammonia.  Ammonia burns in air:

13.  At 750-900 deg C in the presence of a catalyst (platinum, platinum-rhodium) :  NO reacts on with O2 to form the mixed oxides which can be absorbed in water to form nitric acid.

14.  The sequence in industrial utilisation of atmospheric nitrogen is  Ammonia is extremely soluble in water.

15.  Ammonium salts  Crystalline salts of ammonium are mostly water soluble.  Ammonium salts generally resemble those of potassium and rubidium in solubility and structure. The three ions have comparable radii.

17.  Hydrazine can be described as a reaction of ammonia with one ammonia as the substituent.  2 series of hydrazinium salts can be obtained:  N 2 H 5 + are stable in water  N 2 H 6 2+ are hydrolysed in water.

18.  Anhydrous hydrazine is a fuming colorless liquid. It is considerable stable and burns in air  Aqueous hydrazine is a powerful reducing agent in basic solution.  Hydrazine is synthesized by the inateraction of aqueous ammonia with sodium hypochlorite

19.  But there is a competing reaction when hydrazine first is formed:  To prevent this reaction one needs to add gelatine. It complexes Cu 2+ ions better than EDTA.

20.  Hydroxylamine is a weaker base than NH 3 :  It is prepared by reduction of nitrates or nitrites either electrolytically or with SO 2 under controlled conditions.  Hydroxylamine is a white unstable solid.  It is used as a reducing agent.

21.  Heavy metal azides are explosive and lead or mercury azides have been used in detonation caps.  The pure acid is a dangerously explosive liquid.  It can act as a ligand in metal complexes, it is linear molecule.

22.  Dinitrogen monoxide  It has a linear structure is realtively unreactive, is inert towards:  Halogens,  Alkali metals  Ozone at RT.  It is used as an anaesthetic.

23.  Nitrogen monoxide

24.  Dinitrogen trioxide  The anhydride of nitrous acid

28.  Phosphorous occurs in minerals of the apatite family.  As, Sb,Bi occur mainly as sulfide minerals.  The electron configuration is ns 2 np 3.  P and N are very different in their chemistry.  P is a true non metal, down the period the metallic trend is increasing.

29.  Differences between N and P: 1. Diminished ability to form p π - p π multiple bonds 2. The possibility to use the lower 3d orbitals  Nitrogen forms esters, phosphorus gives P(OR)3. Nitrogen oxides and oxoacids involve multiple bonds, whereas the phosphorus oxides have single bonds. Phosphoric acid PO(OH) 3 in contrast NO 2 (OH).

30.  Phosphorus is obtained by reduction of phosphate rocks.  Phosphorus distills and is condensed in water.  White P is stored under water to protect from air.  Red and black P are stable in air, burn on heating.  P is soluble in organic solvents.

31.  As,Sb,Bi are obyained by reduction of the oxides with carbon or Hydrogen.  All elements react readily with halogens.  Nitric acid  Phosphoric acid, arsenic acid, Sb trioxide and Bi nitrate.  Interactions with metals gives phosphides, arsenides,....  GaAs has semiconductor properties.

32.  The stability of the hydrides decreases down the period.  Sb and Bi hydrides are very unstable.  Phosphine is made from the reaction of acids with zinc phosphide.  Phosphine is a nerve toxin..

33.  Trihalides are obtained by direct reaction with halogens.  They rapidly hydrolize in water  Gaseous molecules have pyramidal structure.  Iodides of As,SB,and Bi have layer structures based on hexagonal closed packing of iodine atoms with the group VB elements.  Phosphorus trifluoride is a colorless toxic gas.  It is slowly attacked by water and rapidly by alkali.

35.  Phosphorus pentoxide (P 4 O 10 )  It is used as one of the most effective drying agents. Reacts with water to form phosphoric acid

36.  Phosphoric acid:  PCl3 or P4O6 are hydrolised in water  Phosphorus acid Hypophosphorus acid

37.  Orthophosphoric acid  Is the oldest known phosphorus compounds. It is a syrupy liquid made by direct reaction of ground phhosphate rock with sulfuric acid.  The pure acid is a colorless cyrstalline solid.  Stable and has no oxidising properties below 350- 400 degC.  It will attack quartz.  Hydrogen bonding persists in the concentrated solution and is respåonsible ofr the syrupy behaviour.