Hybridization electronic

Trivalent ( classical carbenium ions contain an sp -hybridized electron-deficient carbon atom, which tends to be planar in the absence of constraining skeletal rigidity or steric interference. The carbenium carbon contains six valence electrons thus it is highly electron deficient. The structure of trivalent carbocations can always be adequately described by using only two-electron two-center bonds (Lewis valence bond structures). CH3 is the parent for trivalent ions. 

To illustrate this rule, consider the ethylene (C2H4) and acetylene (C2H2) molecules. You will recall that the bond angles in these molecules are 120° for ethylene and 180° for acetylene. This implies sp2 hybridization in C2H4 and sp hybridization in C2H2 (see Table 7.4). Using blue lines to represent hybridized electron pairs,... 

Two of the four electrons of the beryllium atom are valence electrons. The bonding in the metallic solid must be accomplished by a combination of 2s and 2p orbitals if not, the s band would be completely filled and Be would be an insulator, or perhaps not a room-temperature solid at all. In the orbital description, the two valence electrons of each Be atom participate in two 2s2p hybrid electron pair bonds, spread over the 12 nearest neighbors of the hep structure. 

Parra, V., Arrieta, A. A., Fernandez-Escudero, J. A., Iniguez, M., De Saja, J. A., and Rodriguez-Mendez, M. L. (2006a). Monitoring of the ageing of red wines in oak barrels by means of an hybrid electronic tongue. Anal. Chim. Acta 563(1-2), 229-237. 

Winquist, F., Flolmin, S., Krantz-Rulcker, C., Wide, P., and Lundstrom, 1. (2000). A hybrid electronic tongue. Anal. Chim. Acta 406(2), 147-157. 

Figure 10.19 Schematic representation of the operational principle of the DNA sensor based on conformational flexibility change in the PNA probe structure stimulated by hybridization, (a) before hybridization, electron transfer between Fc and electrode is possible and (b) after hybridization, formation of the duplex rigidifies the probe structure, preventing efficient electron transfer. Reproduced by permission from Ref. 140 of The Royal Society of Chemistry.

Towards fabrication of SWNT-based molecular electronic devices, two methods have been used to assemble the 03-SWNTs on functionalized SAMs of OPEs, as shown in Figure 5.10. The first, termed chemical assembly , is based on a condensation reaction between the carboxylic acid functionalities of O3-SWNTs and the amine functionalities of SAMs to form amides. The results show that O3 -SWNTs coat the amino-terminated SAM with a high degree of surface coverage. The second method is based on physical adsorption via layer-by-layer (LBL) deposition with bridging of metal cations, i.e., Fe3+ on carboxylate terminated SAMs or Cu2+ on thiol-terminated SAMs. The oxidatively shortened 03 -SWNTs are shown to be perpendicular to the surface with random adsorption of longer tubes. The patterned nanotube assemblies may be useful in hybridized electronic devices, where device functions can be modified by the orientation and stacking of SWNTs, and the properties of the SAM. 

Two atoms, having one s electron each, on molecule formation give a <7 bond e.g. Hg and Lig an s electron of one atom and a p electron or hybridized electron of another atom also give a a bond, as in such links as H—Cl, O—H, N—H and G—H in HgO there are two, in NH3 three, and in GH4, four or bonds. If two atoms form multiple bonds, then only one of these will be a or bond and the remainder tt bonds. 

In order to derive the tetrahedral hybrid electron functions we shall follow the method of Pauling and show that the linear combination of one s and three p wave functions give maximum stability of the bond. The linear combination has the form ... 

For the hybridization of one s and two p electrons, the s function is divided equally amongst the three resulting hybrid functions, so that into each hybrid electron orbital there enters one third of the s cloud i.e. fl2 1/3). The first orbital may therefore be represented by... 

Formation of XeF2 molecule by sp3d hybridization. Electrons supplied by fluorine atoms are represented by dotted arrows. 

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