Mention the difference between Co-ordination compound and Double Salt.

Co-ordination compound Double Salt 1. A complex salt is a compound composed of a central metal atom having coordination bonds with ligands around it. 1. A double salt is a compound prepared by the combination of two different salt components. Co-ordination compound Double Salt 2. They do not completely dissociate into its ions in water. 2. These are completely dissociated into its ions in water. 3. Example is K 4 [ Fe ( CN ) 6 ] . 3. Example is K 2 SO 4 . Al 2 ( SO 4 ) 3 . 24 H 2 O .

Why do transitional elements form Complex compounds?

Transition metals are d -block elements with valence shell configuration ns 2 ( n − 1 ) d 1 − 10 . These metals and their ions easily coordinate with a number of negative ions or neutral molecules having lone pairs of electrons to form a complex. This is due to small size and high nuclear charge of these metals and availability of vacant d -orbitals of suitable energy to accommodate lone pairs of electrons donated by the ligands.

Give an example of each of the following (a) Geometrical isomerism (b) Optical isomerism

Geometrical isomerism arises in heteroleptic complexes due to different possible geometric arrangements of the ligands. The example exhibits the cis-trans geometric isomerism. Optical isomers are mirror images that cannot be superimposed on one another. These are called as enantiomers. The two forms are called dextro (d) and laevo (l) depending upon the direction they rotate the plane of polarised light, example is

Give a brief account of Valence Bond Theory.

The postulates of VBT are as follows∶ (i) Overlapping of two distinct atomic orbital, each having an unpaired electron, results in formation of covalent bond. (ii) Both the electrons, from atomic orbitals, occupy the bond orbital and have opposite spins. Each electron now belongs to both the atomic nuclei. (iii) The strength of chemical bond formed depends on the extent of atomic overlapping. Greater is the extent of overlapping, stronger is the bond formed and larger is the bond energy. (iv) Sigma bonds and pi bonds differ in the type of atomic orbitals overlap. In pi bonds, sideways overlapping happens whereas in sigma bonds the overlapping is along the axis.

NiCl 4 2 - is paramagnetic while Ni ( CO ) 4 is diamagnetic though both are tetrahedral. Why?

From the valence bond theory we came to know that both the compounds NiCl 4 2 - and Ni CO 4 are tetrahedral, but their magnetic characters are different. This is due to a difference in the nature of ligands. Since Cl - is a weak field ligand and it does not cause the pairing of unpaired electrons present in 3 d orbital of the central metal ion. Thus, NiCl 4 2 - is paramagnetic. In case of Ni CO 4 , the oxidation state of Ni is in the zero i.e., thus it has electronic configuration of 3 d 8 4 s 2 . Being a strong field ligand CO is able to cause the pairing of unpaired electrons present in 3 d orbital of the central metal ion. Also, it causes the 4 s electrons to shift to the 3 d orbital, resulting in the sp 3 hybridization of the central metal ion. Since no unpaired electrons are present in the d -orbital of Ni in case of Ni CO 4 , hence it is diamagnetic in nature.

NiCl 4 2 - is paramagnetic, while Ni CO 4 is diamagnetic, why?

In both Ni Cl 4 2 - and Ni CO 4 the hybridisation is sp 3 , but they differ in their magnetic nature. In Ni Cl 4 2 - oxidation state of Ni is + 2 having a configuration of Ar 3 d 8 4 s 0 . Cl - being a weak field ligand is unable to cause pairing of electrons and therefore results in sp 3 hybridisation with unpaired electrons. Thus, the complex is paramagnetic in nature. In the case of Ni CO 4 oxidation state of Ni is 0 having a configuration of Ar 3 d 8 4 s 2 . CO being a strong field ligand causes the pairing of 3 d electrons and also the shift of 4 s electrons to 3 d orbital. So it results in sp 3 hybridisation with no unpaired electrons and thus the complex is diamagnetic in nature. NiCl 4 2 - is paramagnetic, while Ni CO 4 is diamagnetic.

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The oxidation state of iron in $K_{4} [Fe {(CN)}_{6}]$ is

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