Transcript The chemistry of Nitrogen and main group VI

Chapter 16
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Nitrogen can complete its valence valence shell
by:
1.) Electron gain: N3- ion
 This is found in saltlike nitrides.
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2.) formation of electron pair bonds:
 A) single bonds NH3
 B) multiple bonds :N≡N: ; -N=N-, or NO2
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3.) formation of electron pair bonds with
electron gain, NH2- or NH24.) Formation of electron pair bonds with
electron loss (substituted ammonium ions)
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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)
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3.) in few cases 3-covalent nitrogen is planar;
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N-N single bond energy
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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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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.
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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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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 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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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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Ammonia is formed by the action of a base on
an ammonium salt:
Industrially Ammonia is made by the haberBosch process at 400-500 deg C and 1001000atm.
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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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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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The sequence in industrial utilisation of
atmospheric nitrogen is
Ammonia is extremely soluble in water.
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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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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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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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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 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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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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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 monoxide
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Dinitrogen trioxide
The anhydride of nitrous acid
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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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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).
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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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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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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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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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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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Phosphoric acid:
PCl3 or P4O6 are hydrolised in water
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Phosphorus acid
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Hypophosphorus acid
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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 350400 degC.
It will attack quartz.
Hydrogen bonding persists in the concentrated
solution and is respåonsible ofr the syrupy
behaviour.