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The chemistry of Nitrogen. Chapter 16. Nitrogen. 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
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The chemistry of Nitrogen Chapter 16
Nitrogen • Nitrogen can complete its valence valence shell by: • 1.) Electron gain: N3- 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 NO2 • 3.) formation of electron pair bonds with electron gain, NH2- or NH2- • 4.) Formation of electron pair bonds with electron loss (substituted ammonium ions)
Nitrogen • Three-Covalent Nitrogen • NR3 molecules are sp3 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(NH3)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)
Nitrogen • 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.
Multiple bonds • Nitrogens propensity to form pπ- pπ multiple bonds is a feature that distinguishes it from phosphorus and the other GroupVB elements. • N2 has a high bond strength and a short internuclear distance (1.094Å). P forms infinite layer structures with only single bonds or P4 molecules. • The oxo anions NO2- and NO3- , multiple bonds may be formulated in either resonance or MO terms.
Nitrogen • Nitrogen occurs as dinitrogen. N2 (bp 77.3 K). • 78% of the atmosphere is N2 • N14/N15 has a ratio of 272. • N15 compounds are used in tracer studies. • The NN triple bond is responsible for the inert behaviour of N2. • N2 is prepared by liquefaction and fractionation of air.
Nitrogen • N2 only reacts with Li to give Li3N. • With certain transition metal complexes oand with nitrogen fixing bacteria. • Typical reactions of N2 at elevated temperatures :
Nitrides • Nitrides of eletropositives metals have structures with discrete nitrogen atoms and can be regarded as ionic (Ca2+)3(N3-)2 • The Nitrides hydrolyse to ammonia and metal hydroxides. • Preparation: • Direct interaction • Loss of ammonia from amides on heating
Nitrides • 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,S4N4,P3N5) • These nitrides have very differing properties, depending on the element.
Nitrogen Hydrides • 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.
Nitrogen hydrides • 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:
Nitrogen hydrides • 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.
Nitrogen hydrides • The sequence in industrial utilisation of atmospheric nitrogen is • Ammonia is extremely soluble in water.
Ammonium salts • 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.
Hydrazine • Hydrazine can be described as a reaction of ammonia with one ammonia as the substituent. • 2 series of hydrazinium salts can be obtained: • N2H5+ are stable in water • N2H62+ are hydrolysed in water.
Hydrazine • 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
Hydrazine • But there is a competing reaction when hydrazine first is formed: • To prevent this reaction one needs to add gelatine. It complexes Cu2+ ions better than EDTA.
Hydroxylamine • Hydroxylamine is a weaker base than NH3: • It is prepared by reduction of nitrates or nitrites either electrolytically or with SO2 under controlled conditions. • Hydroxylamine is a white unstable solid. • It is used as a reducing agent.
Azides • 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.
Nitrogen oxides • 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.
Nitrogen oxides • Nitrogen monoxide
Nitrogen oxides • Dinitrogen trioxide • The anhydride of nitrous acid
Phosphorous, Arsen, Anitmony, Bismuth • Phosphorous occurs in minerals of the apatite family. • As, Sb,Bi occur mainly as sulfide minerals. • The electron configuration is ns2np3. • P and N are very different in their chemistry. • P is a true non metal, down the period the metallic trend is increasing.
Phosphorus • Differences between N and P: • Diminished ability to form pπ- pπ multiple bonds • 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 NO2(OH).
Elements • 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.
Elements • 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.
Hydrides • 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..
Halides • 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.
Oxides • Phosphorus pentoxide (P4O10) • It is used as one of the most effective drying agents. Reacts with water to form phosphoric acid
Oxo acids • Phosphoric acid: • PCl3 or P4O6 are hydrolised in water • Phosphorus acid Hypophosphorus acid
Oxo acids • 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.
