Valence shell electron pair repulsion trigonal planar geometry

Valence shell electron-pair repulsion (VSEPR) model (Section 1.10) Method for predicting the shape of a molecule based on the notion that electron pairs surrounding a central atom repel one another. Four electron pairs will arrange themselves in a tetrahedral geometry, three will assume a trigonal planar geometry, and two electron pairs will adopt a linear arrangement. 

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. 

The valence shell electron pair repulsion theory states that electron pairs aroimd the central atom of the molecule arrange themselves to minimize electronic repulsion the electrons orient themselves as far as possible from each other. Two electron pairs around the central atom lead to a linear arrangement of the attached atoms three indicate a trigonal planar arrangement, and four result in a tetrahedral geometry. Both lone pair and bonding pair electrons must be taken into accoimt when predicting structure. Molecules with fewer than four and as many as five or six electron pairs around the central atom also exist. They are exceptions to the octet rule. 

Use valence shell electron pair repulsion (VSEPR) to predict geometry about any carbon or nitrogen atom. Count the number of other atoms attached to it and add to that the number of lone pair(s) it may contain. Two = linear and sp hybridized 3 = trigonal planar and sp2 hybridized 4 = tetrahedral and sp3. Not complicated. 

The concept of valence-shell electron-pair repulsion (VSEPR) is presented in introductory organic chemistry as a way to predict molecular geometries. The idea behind VSEPR is that areas of electron density repel each other so that the geometry of bonds and/or lone pairs of electrons around any one atom places these areas as far apart as possible. Por four areas of electron density a tetrahedral geometry is predicted. Eor three areas of electron density a trigonal planar geometry is predicted. Two areas of electron density lead to a linear geometry. 

Molecular geometry Tetrahedron tetrahedral Trigonal (triangular) planar Valence shell electron-pair repulsion theory (VSEPR) Section 13.3 Angular Bent... 

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