Lewis electron pair

AIM theory provides a physical basis for the theory of Lewis electron pairs and the VSEPR model of molecular geometry. Equipped with computers and computer-generated, three-dimensional electron density maps, scientists are able to view molecules and predict molecular phenomena without even having to get off their chairs ... 

Although many other acid-base definitions have been proposed and have been useful in particular types of reactions, only a few have been widely adopted for general use. Among them are those attributed to Arrhenius (based on hydrogen and hydroxide ion formation), Br0nsted-Lowry (hydrogen ion donors and acceptors), and Lewis (electron pair donors and acceptors) [6,67-70]. 

Lewis defined a base as an electron pair donor and an acid as an electron pair acceptor. Lewis electron pair donor was the same as Bronsted-Lowry s proton acceptor, and therefore, was an equivalent way of defining a base. Lewis acids were defined as a substance with an empty valence shell that could accommodate a pair of electrons. This definition broadened the Bronsted-Lowry definition of an acid. The three definitions of acids and bases are summarized in Table 13.3. 

Other simplified quantum treatments, such as the Lewis electron pair and orbital overlap models, have proved useful in teaching and they give qualitative predictions of the structures of molecular compounds, but they become unwieldy when applied to solids. They have not proved to be particularly helpful in the description of the complex structures found in inorganic chemistry and have therefore not been widely used in this field. 

The acidity of a clay can be either of the Brpnsted (H+ donor) or Lewis (electron pair acceptor) type. Even at temperatures below 100 °C, tertiary carbocation intermediates can be generated on clays with high Brpnsted acidity through protonation of the C=C double bond in secondary alkenes, as in the clay-catalyzed formation of MTBE from methanol and isobutene ... 

Exercise 2-1 Draw the Lewis electron-pair structure of 2-propanone (acetone) clearly showing the bonding and nonbonding electron pairs in the valence shell of each atom. Draw structural formulas for other compounds having the composition C3H60 that possess... 

Draw Lewis electron-pair structures for the following substances whose structural formulas are given. Use distinct, correctly placed dots for the electrons and show... 

An advantage of VSEPR is its foundation upon Lewis electron-pair bond theory. No mention need be made of orbitals and overlap. If you can write down a Lewis structure for the molecule or polyatomic ion in question, with all valence electrons accounted for in bonding or nonbonding pairs, there should be no difficulty in arriving at the VSEPR prediction of its likely shape. Even when there may be some ambiguity as to the most appropriate Lewis structure, the VSEPR approach leads to the same result. For example, the molecule HIO, could be rendered, in terms of Lewis theory as ... 

At a later date, however, it was the MO approach that carried the day. The main reason for its success was not only its conceptual simplicity, but also the mathematical convenience of the orbited orthogonality that drastically simplified any quantitative computations. Only relatively recently, and thanks to our better understanding of suitable AO-like basis sets [30], has the VB approach, with its appeal to a chemist s intuition and its direct link with Lewis electron pairing ideas started to enjoy a definite renaissance... 

The physical basis of the Lewis electron pair model... 

G.A. GALLUP, The Lewis electron-pair model, spectroscopy and the role of the orbital picture describing the electronic structure of molecules. 

The nature of this catalytically active zeolite can be either Bronsted (proton donor) or Lewis (electron-pair acceptor) acidic, with protons attached to the framework tetrahedra or not (Figure 7.19). 

Equation (42) shows that the binding force can only be large if the electronic density has important values in the intemuclear region, which means that a certain number of electrons must visit this region. As stated by Feynman (1939) It is clearly seen that concentrations of charge between atoms lead to strong attractive forces, and hence, are properly called valence bonds. This conclusion may be considered as a quantitative justification of the Lewis electron pair sharing concept. 

The extent to which individual electron pairs are localized in distinct spatial regions has been carefully analyzed by Bader and Stephens (1975) using the minimum fluctuation criterion. These authors arrive at the conclusion that the model of spatially localized pairs is appropriate for LiH, BeH2, BH3, and BH-r, it is borderline for CH4, but in NHj, OH2, FH, Ne, N2, and F2, the motions of the valence electrons are so strongly inter-correlated, the localized pair model ceases to afford a suitable description. Moreover, their results provide no physical basis for the view that there are two separately localized pairs of nonbonded electrons in H20. This clearly shows the limit of the Lewis electron pair concept which otherwise has practically disappeared in Linnett s theory. 

Lewis electron-pair acceptor electron-pair donor... 

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