Bonds orbital hybridisation

A covalent bond between two atoms requires two electrons and two orbitals, one for each atom.f The factors determining the properties of the covalent bonds formed by an atom are primarily the number and nature of the orbitals (hybridised bond orbitals) available to the atom, and the number of electrons that it can use in bond formation without losing its electrical neutrality. The opportunities for stabilisation through resonance of covalent bonds among alternative positions are also important. 

For elements adjacent to the noble gases the principal orbitals used in bond formation are those formed by hybridisation of the s and p orbitals. For the transition elements there are nine stable orbitals to be taken into consideration, which in general are hybrids of five d orbitals, one s orbital, and three p orbitals. An especially important set of six bond orbitals, directed toward the comers of a regular octahedron, are the d2sps orbitals, which are involved in most of the Werner octahedral complexes formed by the transition elements. 

C j becomes sp3 hybridised bonding orbital. These terminal p orbitals also overlap the other p orbitals coming in between. Thus these are two stereochemically different ways in which the overlap can take place in the formation of a cyclic structure. 

A PowerPoint presentation covering molecular orbitals, hybridisation and the bonding continuum can be downloaded from www. brightredbooks.net... 

Hyperconjugation of C H Bonds with C H Bonds. Using hybridised orbitals for C H bonds, and mixing them in the usual way to show conjugation, creates the molecular orbitals of Fig. 2.13, which is set up for the anti-periplanar interaction. There is an equivalent set of orbitals interacting in a syn-coplanar arrangement, the relative merits of which are discussed on pp. 98-100. 

It will be noticed that we have been using a combination of molecular orbital theory and valence bond theory (hybridisation) to describe the last few molecules. It happens that a satisfactory picture may be obtained in this way. In other words we have considered the molecular orbital in relation to the two carbon atoms and not over the whole molecule, as would be possible on a molecular orbital theory alone. Also we have only considered the... 

We know that both carbons of an alkene are sp hybridised. But, this is changed when a carbocation is formed (Fig. C). When an alkene reacts with an electrophile like a proton, both electrons in the n bond are used to form a new o bond to the electrophile. Due to this the carbon which gains the electrophile becomes an sp centre. The other carbon containing the positive charge remains as an sp centre. Thus, it has three s/T hybridised orbitals (used for the three o bonds still present) and one vacant 2p orbital which is not involved in bonding. Hyperconjugation involves the overlap of the vacant 2p orbital with a neighbouringC-H c-bond orbital (Fig. D). 

Hybridisation is not a special effect in which precise participation by, for example, one s and three p orbitals produces four sp hybrid orbitals. Continuous variability is possible. The extent to which hybridisation occurs depends on the energy separation of the initial s and p orbitals. The closer they are energetically, the more complete will be the hybridisation. Hybridisation can also occur with d and f orbitals. Hybridisation is no more than a convenient way of viewing the manner in which the electron orbitals interact during chemical bonding. The shape of various hybrid orbitals is given in Table 2.5. 

Figure 2.39 Energy bands from isolated atoms in germanium (Ge). As the spacing between the atoms, r, decreases, first orbital hybridisation occurs and then energy bands develop. These are broad and separated by a narrow energy gap, as expected from the covalent model of bonding...

Borazine, N3B3H6, is isoelectronic and isostructural with benzene. See Section 14.4. The NB bond distance, 144 pm, is intermediate between the bond distances in the planar and orthogonal forms of aminoborane. The bonding may be described in terms of molecular orbitals similar to those of benzene each N or B atom may be regarded as sp hybridised and to form three 2c, 2ea-bonds to its nearest neighbors. Six valence electrons occupy the three r-bonding orbitals formed by combination of the six 2p AOs as indicated in the Fig. 16.9. Compare with the corresponding orbitals in benzene. Fig. 14.6. 

Table 6. Non-bonding orbitals localised on the central atom and not hybridised...

---