CBSE Class-12 Chemistry Quick Revision Notes
Chapter-09: Co-ordination Compounds
Ço-ordination compounds:
a) A coordination compound contains a central metal atom or ion surrounded by
number of oppositely charged ions or neutral molecules. These ions or nmolecules re
bonded to the metal atom or ion by acoordinate bond.
b) Example: K4[Fe(CN)e]
c) They do not dissociate into simple ions when dissolved in water.
Double salt
a) When two salts in stoichiometric ratio are crystallised together from their saturated
solution they are called double salts
b) Example:FeSO4.(NH)2S04.6H20 (Mohr's salt)
c) They dissociate into simple ions when dissolved in water.
Coordination entity:
a) A coordination entity constitutes a central metal atom or ion bonded to a fixed
number of ions or molecules.
b) Example: In K4[Fe(CN)e), [Fe(CN)6]+ represents coordination entity.
Centralatom or ion:
a) In a coordination entity, the atom/ion to which a fixed number of ions/groups are
bound in adefinite geometrical arrangement around it, is called the central atom or
ion.
b) Example: In K4[Fe(CN)6],Fe²+ is the central metal ion.
Ligands:
a) A molecule, ion or group that is bonded to the metal atom or ion in a complex or
coordination compound by a coordinate bond is called ligand.
b) It may be neutral, positively or negatively charged.
) Examples: H20, CN:, NO* etc.
Donor atom:
a) An atom of the ligand attached directly to the metal is called the donor atom.
b) Example: In the complex K4[Fe(CN)6], CN isa donor atom.
Coordination number:
a) The coordination number (CN) of a metal ion in a complex can be defined as the
number of ligand donor atoms to which the metal is directly bonded.
b) Example: In the complex K4[Fe(CN)6], the coordination number of Fe is 6.
Coordination sphere:
a) The central atom/ion and the ligands attached to it are enclosed in square bracket
and are collectively termed as the coordination sphere.
b) Example: In the complex K4[Fe(CN)e], [Fe(CN)e]4 is the coordination sphere.
Counter ions:
a) The ions present outside the coordination sphere are called counter ions.
b) Example: In the complex K4[Fe(CN)e], K+ is the counter ion.
Coordination polyhedron:
a) The spatial arrangement of the ligand atoms which are directly attached to the
central atom/ ion defines a coordination polyhedron about the central atom.
planar and
common coordination polyhedra are octahedral, square
b) The most
tetrahedral.
square planar, Ni(CO), is tetrahedral while [Cu(NH3)6]3+ is
c) Examples: [PtCl4]2- is
octahedral.
Charge on the complex ion: the algebraic sum of the charges on all the
on the complex ion is equal to
The charge
ligands coordinated to the central metal ion.
Denticity:
called denticity.
The number of ligating (linking) atoms present in ligand is
Unidentate ligands: atom are called
a) The ligands whose only one donor atom is bonded to metal
unidentate ligands
b) Examples: H0, NHa, CO, CN
Didentate ligands:
through which they are bonded
a) The ligands which contain two donor atoms or ions
to the metal ion.
nitrogen atoms, oxalate ion
b) Examples: Ethylene diamine (H2NCH2CH2NH2) has two
CO0
COO metal atom.
has two oxygen atoms which can bind with the
Polydentate ligand:
a single ligand, the ligand is called
a) When several donor atoms are present in
polydentate ligand.
Examples: In N(CH;CH2NH2)3, the ligand is said to be polydentate and
b) ligand. It can
Ethylenediaminetetraacetate ion (EDTA4-) is an important hexadentate
atoms to a central metal ion.
bind through two nitrogen and four oxygen
Chelate:
inorganic metal complex in which there is a close ring of atoms caused by
a) An
attachment of a ligand toa metal atom.at two points.ethylene diamine and cupric ion,
formedbetween
b) An example is the complex ion
[Cu(NH2CH2NH2)2]2*.
6Ambidentate ligand: different atoms present in it are called
can ligate (link) through two
a) Ligands which
ambidentate ligand.
Here, NO2- can link through N as well as 0 while SCN can link
b) Example: NO2and SCN-.
throughS as well as N atom.
theory:
