The chemistry of Nitrogen

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The chemistry of Nitrogen

• Chapter 16

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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 NN -NN-, 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)

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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)63
• 2.) Pyramidal molecules (NRRR) 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)

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Inversion of Nitrogen
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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.

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Multiple bonds

• Nitrogens propensity to form pp- pp 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.

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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.

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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
  

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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

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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.

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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.

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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

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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.

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Nitrogen hydrides

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

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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.

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Thermal decomposition of ammonium salts
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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
• N2H6 2 are hydrolysed in water.

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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

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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.

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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.

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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.

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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.

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Nitrogen oxides

• Nitrogen monoxide

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Nitrogen oxides

• Dinitrogen trioxide
• The anhydride of nitrous acid

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Summary of reactions
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Summary of reactions
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Summary of reactions
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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.

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Phosphorus

• Differences between N and P
• Diminished ability to form pp- pp 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).

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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.

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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.

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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..

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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.

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Important reactions of P and Halides
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Oxides

• Phosphorus pentoxide (P4O10)
• It is used as one of the most effective drying
  agents. Reacts with water to form phosphoric acid

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Oxo acids

• Phosphoric acid
• PCl3 or P4O6 are hydrolised in water
• Phosphorus acid Hypophosphorus acid

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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.

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Summary of Group trends
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Summary of reactions of P4
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Summary of reactions of PCl5