Repulsive model

VSEPR model Valence Shell Electron Pair Repulsion model, used to predict molecular geometry states that electron pairs around a central atom tend to be as far apart as possible, 180-182... 

The Lewis structures encountered in Chapter 2 are two-dimensional representations of the links between atoms—their connectivity—and except in the simplest cases do not depict the arrangement of atoms in space. The valence-shell electron-pair repulsion model (VSEPR model) extends Lewis s theory of bonding to account for molecular shapes by adding rules that account for bond angles. The model starts from the idea that because electrons repel one another, the shapes of simple molecules correspond to arrangements in which pairs of bonding electrons lie as far apart as possible. Specifically ... 

Example the n = 2 shell of Period 2 atoms, valence-shell electron-pair repulsion model (VSEPR model) A model for predicting the shapes of molecules, using the fact that electron pairs repel one another. 

Having introduced methane and the tetrahedron, we now begin a systematic coverage of the VSEPR model and molecular shapes. The valence shell electron pair repulsion model assumes that electron-electron repulsion determines the arrangement of valence electrons around each inner atom. This is accomplished by positioning electron pairs as far apart as possible. Figure 9-12 shows the optimal arrangements for two electron pairs (linear),... 

Once computed on a 3D grid from a given ab initio wave function, the ELF function can be partitioned into an intuitive chemical scheme [30], Indeed, core regions, denoted C(X), can be determined for any atom, as well as valence regions associated to lone pairs, denoted V(X), and to chemical bonds (V(X,Y)). These ELF regions, the so-called basins (denoted 2), match closely the domains of Gillespie s VSEPR (Valence Shell Electron Pair Repulsion) model. Details about the ELF function and its applications can be found in a recent review paper [31],... 

The VSEPR (Valence shell electron pair repulsion) Model... 

VSEPR Model valence shell electron pair repulsion model, model used to predict the geometry of molecule based on distribution of shared and unshared electron pairs distributed around central atom of a molecule... 

The distortion produced by the lone pairs is traditionally described using the Valence Shell Electron Pair Repulsion Model (VSEPR model) (Gillespie and Hargittai 1991), which assumes that each pair of electrons in the valence shell is... 

Fig. 6.106. The lateral-repulsion model for the explanation of the capacity-potential curve.

After this decrease in capacity, the attracting forces between the metal charge and the ion charge overcome the lateral repulsion forces. The rate of adsorption increases and the capacity also increases after passing through a minimum after the hump. This lateral-repulsion model is able, then, to explain and reproduce the maximum (the hump) and the minimum in the C-qM curve (Table 6.14). 

In a useful series of papers,140-143 Kepert has considered high coordination number stereochemistries, including lanthanide examples, on the basis of a point-charge repulsion model, where the point charges lie on the surface of a sphere and are constrained only by intraligand factors. 

In the valence-shell electron-pair repulsion model, or VSEPR model, we focus attention on the central atom of a molecule, such as the B atom in BF3 or the C atom in C02. We then imagine that all the electrons involved in bonds to the central atom and the electrons of lone pairs belonging to that atom lie on the surface of an invisible sphere that surrounds it (Fig. 3.3). These bonding electrons and lone pairs are regions of high electron concentration, and they repel one another. To minimize their repulsions, these regions move as far apart as possible on the surface of the sphere. Once we have identified the most distant ... 

The rule is based on the electron-bair repulsion model, which postulates that hecanse electron pairs repel each other, they will try to stay as far apart as possible. In trigonal and tetrahedral geometries, the shape will be exactly trigonal (120° bond angles), or exactly tetrahedral (109.5° bond angles) if the electron groups are all equivalent, as for example in BH3 or CH3+ (trigonal), or in CH4 or NH4 + (tetrahedral). 

Suppose that we wish to construct an LCAO bonding model for methane. We set up the problem by defining an, y, z coordinate system and placing the carbon at the origin. The molecule is tetrahedral, as determined from the electron-pair repulsion model. The orientation of the molecule is arbitrary we choose to arrange it as shown in 21, with the hydrogen atoms in the +x, +y, + z quadrant, the —x, —y, +z quadrant, the +, —y, —z quadrant, and the —x, +y, —z quadrant. 

The success of the ligand-ligand repulsion model prompted its adoption as an element of a molecular mechanics program. In the resulting approach the valence angles around the metal ion are modeled solely by nonbonded interactions, using the usual van der Waals potential (for example, Eq. 2.9 kg = 0 in Eq. 2.7 Urey-Bradley approach)136. 6 Again, the fact that the electronic effects responsible for the directionality of bonds are not explicitly modeled here may seem questionable but extensive tests have shown the model to be reliable 371. An explanation for this apparent contra-... 

Proteins are both colloids and polymers. Therefore, attempts have been made to understand the phenomenon of protein aggregation with the help of models from the polymer and colloid fields such as DLVO theory, describing the stability of colloidal particles, or phase behavior and attraction-repulsion models from polymers (De Young, 1993). For faster progress, more phase diagrams for equilibrium protein precipitation, in both the crystalline and the non-crystalline state, as well as more data on observations of defined protein oligomers or polymers, are required. 

R. J. Gillespie, Electron-Pair Repulsion Model for Molecular Geometry, J. Chem. Educ. 1970, 47, 18. R. J. Gillespie, Molecular Geometry, Van Nostrand Reinhold Co., London, 1972. 

Scheme 15 Dipole repulsion models for stereocontrol by alpha-alkoxy substituents...

To confirm the existence of the dipole repulsion effect, a related substrate 54b was conceived, differing only in the configuration at the a-carbon. The expected chair-axial and chair-equatorial transition states for cyclization of 54b each have their C-O and C=N bonds in a gauche relationship the dipole repulsion model therefore predicts minimal differentiation. In this control experiment, cyclization of... 

This chapter reviews molecular geometry and the two main theories of bonding. The model used to determine molecular geometry is the VSEPR (Valence Shell Electron Pair Repulsion) model. There are two theories of bonding the valence bond theory, which is based on VSEPR theory, and molecular orbital theory. A much greater amount of the chapter is based on valence bond theory, which uses hybridized orbitals, since this is the primary model addressed on the AP test. 

Figure 3-3. Potential energy surface for the water dimer obtained at RHF/DZP and fully classical MM levels with various repulsion models. Solid line RHF. Repulsion dashed line unscreened LJ dotted screened LJ bold dotted unscreened X6...

The structures of the binary fluorides are predictable on the basis of the valence shell electron pair repulsion model (see Chapter 2). With eight valence shell electrons from the xenon atom and two additional electrons from the two fluorine atoms, there are 10 electrons surrounding the xenon atom in XeF2. Thus, the structure of XeF2 has Doah symmetry as shown here ... 

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