Transition elements

Crystal Feild Theory (CFT) :-
1. According to CFT the nature of the bond between metal and ligands is 100% ionic.
2. CFT considers the electrostatic attraction forces between metal ion and ligands.
3. CFT recorded as the -ve ligand as a point charges are neutral they approach towards the neutral ion with than -ve en4. CFT considers the metal complex as possitively charged metal ion sorounded by the ligand molecules with their -ve ends.
5. CFT never consider the covalent bond between metal and ligand instead it considered the electrostatic attraction forces between metal and ligand.
6. Whatever ligand molecules approches towards the metal ion. There are electron-repulsion between ligands electrons and metal ion electrons these repulsive forces are responsible for the splitting of d-orbitals of central metal ion. thus the splitting of d-orbitals is the dasis for a CFT.
7. The number of ligands and their arrangement aboyt the metal ion will predict the crystal field, if there are six ligands octahedral crystal feild is produced, if there are 4 ligands tetrahedral or square planar crystal feilds are produced.
8. If there are five ligands square pyramidal or trigonal bipyramidal crystal feild produced.
9. If there are three ligands trigonal planar and two ligands producess crystal feild.
10. The different crystal fields will have different effects of energies of 5 d-orbitals of central metal ion hence splitting of d-orbitals is different in different crystal fields.
11. In the absence of ligands fields the five d-orbitals are in degenerate state. i.e they are energitically equal in the presence of ligand fields the degenaracy is lifted. And splite into various energy levels. The splitting of d-orbitals in the presence of ligands field is known as “Crystal field splitting”.
12. Due to this splitting the energy is lowered and the complex gets stabilised. Thus the decrease of energy due to crystal field splitting of d-orbitals is known as “crystal field stabilisation energy” (CFSE). It is expressed in terms of cm-1,cal/mole, KJ/mole, k.cal/mole….etc.
13. On the basis of splitting of d-orbitals and the electron distribution in these orbitals the properties of metal complex can be explain satisfactories.
14. The magnetic properties of metal complexes can be explain by considering the distribution of electron in various d-orbital energy levels.
15. The colour and spectral properties of metal complexes can be explain on the electronic transitions between energy levels of d-orbitals.
16. The stabity of oxidation state, spiral structures can be explain on the basis of crystal field stabilisation energy.
17. On the bases of CFSE we can explain why certain metal ions will prefer a perticular geometry in a given set of lignds.
18. The hybridisation enegies of aqua complexes of 3d-metal ions & lattice energies of metal halide crystal can be explain on the basis of crystal field stabilisaaation energy,
19. Mullikon assigns symbols for 5d-orbitals on the basis of symmetry.
The splitting of d-orbitals is due to the electron repulsion forces between the metal ion and approaching ligands.
The shifts in the energies, of d-orbitals depends upon the spacial relationship between the orientation of metal d-orbitals and approching ligands.
According to the “low of preservation of centre of gravity”. The algebric sum of energy shifts of all the orbital must be equal to zero. Thus during the splitting of d-orbitals the energies of some orbitals are raised while the energies of other dobitals decreased.
If there is direct interaction between the metal d-orbital and approching ligands then these orbitals are highly establised and the energies of these orbitals are raised.
the decrease of energy of d-orbitals depends upon the magnitude of distance metal d-orbital and approching ligand.
As the distance increases the electron-electron repulsion forces decreases and thus the energy of orbitals are also decreases to a larger extent.
Octahedral Geometry:-
In the case of octahedral complexes the ligands are approching along the co-ordinate axis, along each co-ordinate axis two ligands are approching. Since the lobes of ‘eg’ set of orbitals of metal ion oriented along the approching ligands their experience a greater repulsion forces. Hence the energy of ‘eg’ set is raised by 6Dq, since the lobes of ‘t2g set are oriented in between the approching ligands. Their experience lesser repulsion forces and hence the energy of this set decreased by -4Dq.
Thus the degenaracy of 5d-orbitals is lifted in octahedral geometry.