Molecular Geometry and Bonding

A few examples will illustrate how VSEPR is used to predict molecular geometry. Beryllium chloride, BeCl, has the Lewis structure 

The central beryllium atom has two bonding pairs of electrons. These bonding pairs repel each other and attempt to remain as far 

Now consider boron trifluoride, BF3 in which boron is covalently bonded to three fluorine atoms. For the electron pairs to remain as far apart as possible, the arrangement is triangular with a 120° angle between fluorines  

The Lewis dot structure for BF3 shows the central boron atom being surrounded by only six electrons, which violates the octet rule. This illustrates that the octet rule, while providing general guidelines, has exceptions. 

For a final example, let s consider methane, CH with four bonding electrons surrounding the central carbon atom. VSEPR predicts a tetrahedral arrangement with bond angles of 109.5°. 

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The shapes of the monomeric molecules of the Group 2 halides (gas phase or matrix isolation) pose some interesting problems for those who are content with simple theories of bonding and molecular geometry. Thus, as expected on the basis of either sp hybridization or the... 

We ll ease into the study of organic chemistry by first reviewing some ideas about atoms, bonds, and molecular geometry that you may recall from your general chemistry course. Much of the material in this chapter and the next is likely to be familiar to you, but it s nevertheless a good idea to make sure you understand it before going on. 

R. J. Gillespie, P. L. P. Popelier, Chemical Bonding and Molecular Geometry. Oxford University Press, 2001. 

Chemical bonding and molecular geometry from Lewis to electron densities / R.J. Gillespie, P.L.A. Popelier. 

The electron diffraction molecular structure research is in a fruitful and mutually beneficiary relationship with nonempirical quantum chemical investigations as well as with the development of qualitative models on bonding and molecular geometry. 

VT > Ronald J. Gillespie, James N. MJI Spencer, and Richard S. Moog, "Demystifying Introductory Chemistry Part 2. Bonding and Molecular Geometry Without Orbitals-The Electron Domain Model," /. Chem. Educ., Vol. 73,1996,622-627. 

K. B. Borisenko, C. W. Bock, I. Hargittai, Intramolecular Hydrogen Bonding and Molecular Geometry of 2-Nitrophenol from a Joint Gas-Phase Electron Diffraction and Ab Initio Molecular Orbital Investigation. J. Phys. Chem. 1994, 98, 1442-1448. 

Source A. F. Wells, Structural Inorganic Chemistry, 5th ed., Oxford University Press, New York, 1984, pp. 807,926,933-934 R. J, Gillex-pie and P. L. A. Popelier, Chemical Bonding and Molecular Geometry, Oxford University Press, New York, 2001, p. 117. 

We have described bonding and molecular geometry in terms of valence bond theory. In valence bond theory, we postulate that bonds result from the sharing of electrons in overlapping orbitals of different atoms. These orbitals may be pure atomic orbitals or hybridized atomic orbitals of individual atoms. We describe electrons in overlapping orbitals of different atoms as being localized in the bonds between the two atoms involved. We then use hybridization to help account for the geometry of a molecule. 

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