Question

(a) Give the postulates of Werner's theory of co-ordination compounds.
(b) Differentiate between chemical reactions and nuclear reactions.

Answer 1

(a) Postulates of Werner's theory:
1) Every metal atom has two types of valencies
(i) Primary valency or ionisable valency
(ii) Secondary valency or non ionisable valency
2) The primary valency corresponds to the oxidation state of the metal ion.
The primary valency of the metal ion is always satisfied by negative ions.
3) Secondary valency corresponds to the coordination number of the metal ion or atom. The secondary valencies may be satisfied by either negative ions or neutral molecules.
4) The molecules or ion that satisfy secondary valencies are called ligands.
5) The ligands which satisfy secondary valencies must project in definite directions in space. So the secondary valencies are directional in nature whereas the primary valencies are non-directions in nature.
6) The ligands have unshared pair of electrons. These unshared pair of electrons are donated to central metal ion or atom in a compound. Such compounds are called coordination compounds.
Werner's representation
Werner represented the first member of the series $\left[Co\right(N{H}_3\left)6\right]C{l}_3$ as follows. In this representation, the primary valency (dotted lines) are satisfied by the three chloride ions. The six secondary valencies (solid lines) are satisfied by the six ammonia molecules.

Chemical reaction	Nuclear reaction
(i) In a chemical reaction, the nuclei of the atoms taking part remain unaffected only the electrons in the extra nuclear part of the atoms take part in the chemical process.	In nuclear reaction, the nuclei of the atoms interact with other nuclei or lighter particles or photons resulting in the formation of new nuclei and one or more lighter particles.
(ii) These reactions involve some loss, gain or overlap of outer orbital electrons of the reactant atoms.	These reactions involve emission of alpha, beta and gamma particles from the nucleus.
(iii) A chemical reaction is balanced info mass only.	Nuclear reaction is balanced in terms of both mass and energy.
(iv) The energy changes in chemical reaction is very much less than the nuclear reaction.	The energy changes are far exceed than the energy changes in chemical reactions.
(v) In this reaction, the energy is expressed in terms of kilojoules per mole.	In this reaction, the energy is expressed in MeV per individual nucleus.
(vi) No new element is produced since nucleus is unaffected.	New elements/isotope may be produced during this reaction.
(viii) These reaction are affected by change n temperature and pressure.	These reactions are not affected by temperature and pressure.
(ix) For this reaction law of conservation of mass hold good.	For this reaction, law of mass does not hold good.
(x) The atomic number of the element does not change.	The atomic number of the element changes.