Hybridization valence-shell electron-pair

Now that we know how to determine hybridization states, we need to know the geometry of each of the three hybridization states. One simple theory explains it all. This theory is called the valence shell electron pair repulsion theory (VSEPR). Stated simply, all orbitals containing electrons in the outermost shell (the valence shell) want to get as far apart from each other as possible. This one simple idea is all you need to predict the geometry around an atom. First, let s apply the theory to the three types of hybridized orbitals. 

VSEPR (Valence Shell Electron Pair Repulsion) bonding pairs (X) and lone pairs (E) define geometry of AXn reflects hybridization of A... 

If an attempt were made to apply the rules of valence shell electron pair repulsion theory to radicals, it would not be clear how to treat the single electron. Obviously, a single electron should not be as large as a pair of electrons, but it is expected to result in some repulsion. Therefore, it is difficult to predict whether a radical carbon should be sp2 hybridized with trigonal planar geometry (with the odd electron in a p orbital), sp3 hybridized with tetrahedral geometry (with the odd electron in an sp3 AO), or somewhere in between. Experimental evidence is also somewhat uncertain. Studies of the geometry of simple alkyl radicals indicate that either they are planar or, if they are pyramidal, inversion is very rapid. 

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. 

The hybridized orbital approach is a simplified way of predicting the geometry of a molecule with three or more atoms by mixing the valence orbitals of its central atom. An alternative approach, valence shell electron-pair repulsion (VSEPR) theory, accomplishes the same thing in a more qualitative way. 

The geometry shown is predicted by VSEPR (valence shell electron pair repulsion) theory, in which orbitals containing valence electrons are directed so that the electrons are as far apart as possible. An asterisk indicates a hybridized atom. 

From the valence shell electron-pair repulsion (VSEPR) theory, the steric number of the two outer carbon atoms is 4 (so they are sp hybridized), and that of the two central carbon atoms is 3 (sp hybridized). The bonding around the outer carbon atoms is tetrahedral, and that about the central ones is trigonal planar. Each localized a bond uses two electrons, resulting in a single bond between each pair of bonding atoms. In the case of 2-butene, these placements use 22 of the 24 available valence electrons, forming a total of 11 single bonds. 

Valence Shell Electron Pair Repulsion (VSEPR) Theory Hybridization of Atomic Orbitals, sp, sp, sp Single Bonds Conformational Isomers Pi Bonds Pi Barrier to Rotation C/s and Trans, 2p-3p Triple Bonds Cumulenes... 

Theory is a term that is very widely used by chemists. To take the area of chemical bonding as an example, chemists widely refer to molecular orbital (hereafter MO) theory, valence bond (VB) theory, hybridization theory, valence shell electron pair repulsion (VSEPR) theory, and ligand field theory. And even those probably do not exhaust the list. 

Valence-shell electron-pair repulsion (VSEPR) theory and the concept of hybridization suggest that the water molecule has two O—H bonds and two non-bonded pairs arranged tetrahedrally. More accurate calculations show that this does not provide a true picture of the total electron density in H20. 

Skill 1.3c-Predict molecular geometries using Lewis dot structures and hybridized atomic orbitals, e.g., valence shell electron pair repulsion model (VSEPR)... 

Two theories go hand in hand in a discussion of covalent bonding. The valence shell electron pair repulsion (VSEPR) theory helps us to understand and predict the spatial arrangement of atoms in a polyatomic molecule or ion. It does not, however, explain hoav bonding occurs, ] ist where it occurs and where unshared pairs of valence shell electrons are directed. The valence bond (VB) theory describes how the bonding takes place, in terms of overlapping atomic orbitals. In this theory, the atomic orbitals discussed in Chapter 5 are often mixed, or hybridized, to form new orbitals with different spatial orientations. Used together, these two simple ideas enable us to understand the bonding, molecular shapes, and properties of a wide variety of polyatomic molecules and ions. 

We have already assumed that electron pairs, whether in bonds or as nonbonding pairs, repel other electron pairs. This is manifested in the tetrahedral and trigonal geometry of tetravalent and trivalent carbon compounds. These geometries correspond to maximum separation of the electron-pair bonds. Part of this repulsion is electrostatic, but there is another important factor. The Pauli exclusion principle states that only two electrons can occupy the same point in space and that they must have opposite spin quantum numbers. Equivalent orbitals therefore maintain maximum separation, as found in the sp, sjf, and sp hybridization for tetra-, tri-, and divalent compounds of the second-row elements. The combination of Pauli exclusion and electrostatic repulsion leads to the valence shell electron-pair repulsion rule (VSEPR), which states that bonds and unshared electron pairs assume the orientation that permits maximum separation. 

Knowledge Required (1) The valence-shell-electron-pair-repulsion (VSEPR) model for predicting molecular shape. (2) The valence-bond theory for predicting hybridization of orbitals. 

Valence shell electron pair repulsion, VSEPR. A mental tool used to predict deviations from standard hybridized bond angles based on how much of the surface area of an atom a given electron pair in its outer shell occupies. 

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