NCERT Book Class 12 Chemistry Chapter 5 Coordination Compounds

Unit

Objectives
5
Coordination
After studying this Unit, you will be
able to Compounds
• appreciate the postulates of
Werner’s theory of coordination
compounds;
Coordination Compounds are the backbone of modern inorganic
• know the meaning of the terms: and bio–inorganic chemistry and chemical industry.
coordination entity, central atom/
ion, ligand, coordination number,
coordination sphere, coordination In the previous Unit we learnt that the transition metals
polyhedron, oxidation number, form a large number of complex compounds in which
homoleptic and heteroleptic; the metal atoms are bound to a number of anions or
• learn the rules of nomenclature neutral molecules by sharing of electrons. In modern
of coordination compounds; terminology such compounds are called coordination
• write the formulas and names compounds. The chemistry of coordination compounds
of mononuclear coordination
is an important and challenging area of modern
compounds;
inorganic chemistry. New concepts of chemical bonding
• define different types of isomerism
and molecular structure have provided insights into
in coordination compounds;
the functioning of these compounds as vital components
• understand the nature of bonding
of biological systems. Chlorophyll, haemoglobin and
in coordination compounds in
terms of the Valence Bond and vitamin B12 are coordination compounds of magnesium,
Crystal Field theories; iron and cobalt respectively. Variety of metallurgical
• appreciate the importance and processes, industrial catalysts and analytical reagents
applications of coordination involve the use of coordination compounds.
compounds in our day to day life. Coordination compounds also find many applications
in electroplating, textile dyeing and medicinal chemistry.

5.1 Werner’
Werner’ss Alfred Werner (1866-1919), a Swiss chemist was the first to formulate
his ideas about the structures of coordination compounds. He prepared
Theory of and characterised a large number of coordination compounds and
Coordination studied their physical and chemical behaviour by simple experimental
Compounds techniques. Werner proposed the concept of a primary valence and
a secondary valence for a metal ion. Binary compounds such as
CrCl3, CoCl2 or PdCl2 have primary valence of 3, 2 and 2 respectively.
In a series of compounds of cobalt(III) chloride with ammonia, it was
found that some of the chloride ions could be precipitated as AgCl on
adding excess silver nitrate solution in cold but some remained in
solution.
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