Valence bond theory (VBT)

1. Valence bond theory (VBT) Dr-Najlaaalradadi

2. There are theories as to why the links in the complexes and transition elements, :including Valence Bond Theory (V B T) We will study the hybridization Dr-Najlaa alradadi

3. 1-Type of hybrid orbital's (sp3): A)Interdependence in methane : If we tried to apply the valence bond method prior to the molecules containing many atoms get a big disappointment. In most cases, the bond angles will be derived from the valence bond method for different angles of observation. For example, carbon has a configuration of E (= latency idle state) is: Dr-Najlaa alradadi

4. Therefore we expect that when that when hydrogen reacts with the molecule will give a (CH2), and that corner will be (90 º) is that the molecule (CH2) is stable and that the simplest compound of carbon and hydrogen is methane (CH4). To get the molecular formula and the way the valence bond, we need to plan orbital of carbon has four electrons Single even result in overlapping orbits to the formation of four links (C - H) to such a scheme to imagine that one of electrons from the orbit of (2s) in the carbon absorbed amount of and rose to power over the (2p) empty. Distribution of the resulting electronic excited state is : Dr-Najlaa alradadi

5. This means that hybridization occurs between the orbit (s) and three orbits of (p) consists of four identical orbits, which tend to the corners of the tetrahedral pyramid and intermediate between capacity and energy orbit (s) and orbit (p). Dr-Najlaa alradadi

6. Figure shows the process of hybridization over (s) and orbits (p) to give a series of four orbits of the hybrid type (sp3) an atom of carbon. Dr-Najlaa alradadi

7. In the process of hybridization number of hybrid orbital's is equal to the total count of atomic orbital's United. Figure shows the type of hybrid orbital's (sp3) and the formation of links in methane. Dr-Najlaa alradadi

8. Hybridization on the oxygen atom and nitrogen in the water and ammonia is also of the type (sp3) in the sense that we expect that the value of the angle Association (HOH) and the angle in the (HNH) are (109.5 º) and this value does not differ much from the values ​​measured in practice are (104.5 º) of water and (107.0 º) of ammonia B) Interdependence in the ammonia and water : Dr-Najlaa alradadi

9. We can explain the interdependence of the orbits planned ammonia by nitrogen level equivalence follows Dr-Najlaa alradadi

10. Interdependencein Boron 2-Type of hybrid orbital's (sp2): Can be represented by the type of hybridization (sp2) for the boron atom as follows: Dr-Najlaa alradadi

11. Gives the type of hybridization (sp2) Plane triangle structure so that the angles between the links (120 º) as in (BF3). Dr-Najlaa alradadi

12. Beryllium has four orbits in the level of parity, while only two electrons have 3-Type of hybridization (sp): Therefore, the hybridization of beryllium compounds include round (s) and over (p) to give the kind of hybrid orbits (sp) and remain two of the orbits (p) without hybridization and can be represented as in the form: Dr-Najlaa alradadi

13. Hybridization of the type leads to a linear structure in the sense that the angle of the Association equal to (180 º) as in (BeCl2). Dr-Najlaa alradadi

14. Hybridization schemes are used which include orbits (d) to explain the thread that includes a number of electrons more than (8). 4-Orbits (d) hybrid: In (PCl5), there are five links and this means that there are five orbits of half-packed on the central atom of phosphorus. Hybridization is of course (s) and three orbits of (p) and one of the orbits (d) to give the five orbits of the hybrid type (sp3d). Dr-Najlaa alradadi

15. Hybridization of the type (sp3d) has a structure of the Trigonalbipyramidal as in the picture . 4- Which element can expand its valence shell to accommodate more than eight electrons? A) O B) C C) P D) He Dr-Najlaa alradadi

16. To explain the correlation in (SF6) you need to half-packed six orbits on the sulfur atom where the hybridization between the orbit (s) and three orbits (p) over the two (d) gives the six orbits of the hybrid type (sp3d2) Dr-Najlaa alradadi

17. The six hybrid orbital's of the type (sp3d2) structure has Octahedral, as in the form : Dr-Najlaa alradadi

18. In (CH4), for example the carbon atom composition of four orbits of the hybrid type (sp3) as follows: Electron configuration of carbon: Excited atom Dr-Najlaa alradadi

19. This theory is based mainly on the hybridization of atomic orbital's of the atom or ion Central.  To apply this theory to the transition elements Complexes Pauling suppose the following hypotheses : Dr-Najlaa alradadi

20. 1 - atom central element (Element transition or Lewis acid) can configure orbital's hybrid empty of electrons receive a pair electrons of the group-giving in other words we can say that it will consist of bonds (σ)overlap between orbital'sempty hybrid of the atom central and between the orbital's of group-giving and containing a pair of electrons thus formed coordination bonds .  and that the bond between the central atom and ligand is covalent bond (100%). Dr-Najlaa alradadi

21. 2 - The donor atom or the group-giving or Lewis base must contain an atom where there is at least a pair of electrons. • 3 -In addition to the formation of bonds (σ) there is a possibility to create bonds (π) that are available atomic orbital's contain electrons in central atom overlap with the empty orbital's of the donor atom. Dr-Najlaa alradadi

22. 4- The number of these hybrid orbital's is equal to the number of coordinate of the central atom in complexes . Dr-Najlaa alradadi

23. [Be(H2O)4]2+ Hybridization : (sp3) Geometry : Tetrahydral . (absence of single electrons) Diamagnetic Dr-Najlaa alradadi

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25. [Cr(CO)6] Hybridization : (d2sp3) Geometry : Octahedral Diamagnetic Dr-Najlaaalradadi]

26. [Fe(CO)5] Hybridization : dsp3 TrigonalbipyramidalGeometry : Diamagnetic Dr-Najlaa alradadi

27. [Ni(CN)4]2- Hybridization : dsp2 Geometry : Square planar Diamagnetic Dr-Najlaa alradadi

28. [NiCl4]2- Hybridization : (sp3) Geometry : Tetrahydral Paramagnetic (M.2.8 β ≈ µ) Contains two electrons alone Dr-Najlaa alradadi

29. [Ti(H2O)6]3+ Hybridization : (d2sp3) Geometry : Octahedral Paramagnetic (M.1.7 β ≈ µ) Contains a single electron Dr-Najlaa alradadi

30. [Fe(CN)6]4- Hybridization : (d2sp3) Geometry : Octahedral Diamagnetic Dr-Najlaa alradadi

31. [Fe(H2O)6]2+ Hybridization : (sp3d2) Geometry : Octahedral Paramagnetic (M.4.8 β ≈ µ) Contains four electrons alone Dr-Najlaa alradadi

32. :_Valence bond theory *Several theories currently are used to interpret bonding in coordination compounds. *In the valence bond (VB) theory, proposed in large part by the American scientists Linus Paulingand John C. Slater, bonding is accounted for in terms of hybridized orbital's of the metal ion, which is assumed to possess a particular number of vacant orbitalsavailable for coordinate bonding that equals its coordination number. *Each ligand donates an electron pair to form a coordinate-covalent bond, which is formed by the overlap .. Dr-Najlaaalradadi

33. Valence Bond Theory of Transition Metal Coordination Compounds: *VB theory treats metal to ligand (donor group) bonds as coordinate covalent bonds, formed when a filled orbital of a donor atom overlaps with an empty hybrid orbital on the central metal atom. Dr-Najlaaalradadi

34. The theory considers which atomic orbitals on the metal are used for bonding. • From this the shape and stability of the complex are predicted Dr-Najlaa alradadi

35. *The molecular geometry is predicted using VSEPR. *The theory proposes that the number of metal-ion hybrid orbital's occupied by donor atom lone pairs determine the geometry of the complexes. *Lone pairs of electrons are ignored. Since lone pairs are in the inner shell, they are believed to have little effect on molecular geometry. Dr-Najlaaalradadi

36. Hybridization: *In the formation of covalent bonds, electron orbital's overlap in order to form "molecular" orbital's, that is, those that contain the shared electrons that make up a covalent bond. Although *the idea of orbital overlap allows us to understand the formation of covalent bonds, it is not always simple to apply this idea to polyatomic molecules. Dr-Najlaa alradadi

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39. It must be remembered that: • * Hybrid orbitals do not actually exist. • * Hybridization is a mathematical manipulation of the wave equations for the atomic orbitals involved. Dr-Najlaa alradadi

40. complex formation- VBT • The formation of a complex may be considered as a series of hypothetical steps. • * First the appropriate metal ion is taken, e.g. Co +3, a Co atom has the outer electronic structure 3d7 4S2. Thus a Co+3 ion will have the structure 3d6, and the electrons will be arranged as follows: Dr-Najlaa alradadi

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42. First, with transition metals, as the ion is formed, the valence sand porbitals (4s and 4p, in the case of a first row transition metal such as Co) become higher in energy compared to the valence d orbital (3d in the case of Co).  The six valence electrons of Co3+ can be assigned to the 3d orbitals, following Hund's rule.  Co3+ can coordinate to six ligands (each ligand donating a pair of electrons) which leads to an octahedral complex.  Two examples are shown above, the fluoro complex is an example of a complex anion while the ammonia (ammine) complex is considered a complex cation.  Dr-Najlaa alradadi

43. The above diagram also shows two possibilities for the electronic configuration.  • The fluoro complex keeps the Co electrons in the same configuration as the isolatedCo3+ ion.  • The electrons from the fluoro ligands simply occupy the upper vacant orbitals on Co.  With hybridization, this will be a set of sp3d2hybrid orbitals ( bond formed) outer orbital complex. • The d orbitals used are 4dx2-y2, 4dz2 Dr-Najlaa alradadi

44. Note: • * The energy of these orbitals is quite high so the complex will be reactive or labile. • * The magnetic moment depends on the number of unpaired electrons. • *The 3d level contains the maximum number of electrons for a d6arrangement, and this is called a high–spin or a spin-free complex. Dr-Najlaa alradadi

45. The same type of hybridization can be imagined in the hexaammine complex. • *In this case, however, the electrons originally with Co3+ are forced to pair first and the electrons from the ligands will also occupy the orbitals vacated due to the pairing of the Co electrons to form d2sp3. • * Low energy inner d orbitals are used to form an inner orbital complex.  Dr-Najlaa alradadi

46. * Inner complex is more stable than outer complex. • * The unpaired electrons in the metal ion have been forced to pair up – to form low spin complex. • * In this case for Co+3 all electrons are paired and the complex will be diamagnetic Dr-Najlaa alradadi

47. This happens because ammonia is known to be a "strong" ligand. • From the above example, a drawback of the valence bond theory becomes evident.  • One needs to know first if the ligand is strong enough to cause electrons on the metal to pair first. Dr-Najlaa alradadi

48. ** The metal ion could also form four- coorinate complexes. • Two different arrangements are possible: • *sp3 hybridization – tetrahedral shape. • *dsp2 hybridization- square planar shape Dr-Najlaa alradadi

49. Application of theory to VBT Coordinate Compounds: * Linear complexes: [Cu(CN)2]- Cu=Ar 4s1 3d10 , Cu+1 = Ar 4s0 3d10 Dr-Najlaa alradadi

50. * Octahedral : [Fe(CN)6]3-Fe = Kr 4s2 3d6 Kr 4s0 3d5=Fe+3 Dr-Najlaa alradadi