The ions consisting
of two or more electronegative atoms of which at least one is nitrogen, that
have properties similar to those of halide ions. These ions are called pseudohalide ions, Pseudohalide ions are
univalent and these form salts resembling halide salts. The pseudohalide ions
are :
Cyanide ions (CN-)
Isocyanide ion (NC-)
Cyanate ion (OCN-)
Fulminate ion (ONC-)
Thiocyanate ions(SCN-)
Isothiocyanate ion (NCS-)
Selenocyanate ion (SeCN-)
Tellurocyanate ion (TeCN-)
Azide ion (N3-) :
Azido carbon disulphide ion (SCSN-3)
The best known
pseudohalide is CN-.This resembles Cl- , Br- and I- in the following respects:
(i) It forms an acid, HCN.
(ii) It can be oxidised to (CN)2 molecule.
(iii) It forms insoluble salts with Ag+, Pb2+ and Hg22+
(iv) It forms large number of complexes similar to halide complexes, e.g. [Cu
(CN)4]2- and [CuCl4]2, [Co(CN)6]3-
and [CoCl6]3-
(v) Inter-pseudohalogen compounds ClCN, BrCN and ICN can be
formed.
(vi) AgCN is insoluble in water but soluble in ammonia likeAgCl.
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