What Is the Lewis Model of Bonding

States today. In 1985, however, the International Union of Pure and Applied Chemistry (lUPAC) recommended an alternative system in which the columns are numbered 1 to 18 beginning on the left and without added letters. Although we use the original Mendeleev system in this text, the Periodic Table on the inside back cover of the text shows both. 

2 What Is the Lewis Model of Bonding A. Formation of Ions 

Gilbert N. Lewis (1875-1946) introduced the theory of the electron pair that extended our understanding of covalent bonding and of the concept of acids and bases. It is in his honor that we often refer to an electron dot structure as a Lewis structure. 

Octet rule The tendency among atoms of Group 1A-7A elements to react in ways that achieve an outer shell of eight valence electrons. 

Anion An atom or group of atoms bearing a negative charge. 

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A molecular compound is composed of 60.4% Xe, 22.1% O, and 17.5% F, by mass. If the molecular weight is 217.3 amu, what is the molecular formula What is the Lewis formula Predict the molecular geometry using the VSEPR model. Describe the bonding, using valence bond theory. 

What feature(s) of the Lewis structure of benzene. Model 1, is inconsistent with the calculated C-C bond orders in Model 1 ... 

In the very first chapter of this book, we described the scientific approach and put a special emphasis on scientific models or theories. In this chapter, we looked carefully at a model for chemical bonding (the Lewis model). Why is this theory successful What are some of the limitations of the theory ... 

We have learned that the Lewis model portrays a chemical bond as the transfer or sharing of electrons represented as dots. Valence bond theory portrays a chemical bond as the overlap of two half-filled atomic orbitals. What is a chemical bond according to molecular orbital theory ... 

To understand the structures of organic molecules and how these molecules react, we need a mental picture of the bonds that hold the atoms together. Several different models or pictures are used to describe the chemical bond. Which picture we use depends on what we are trying to accomplish. In this chapter we will learn about the simplest picture, which describes a covalent bond as a shared pair of electrons and uses Lewis structures to represent molecules. Although this model is not complex, it will be adequate for most of our uses. (In Chapter 3 we will look at a more complex model for bonding.) Most of what is covered in this chapter should be a review. 

Recall that the LE model views a molecule as a collection of atoms bound together by sharing electrons between atomic orbitals. The arrangement of valence electrons is represented by the Lewis structure (or structures, where resonance occurs), and the approximate molecular geometry can be predicted using the VSEPR model. In this section we will describe what types of atomic orbitals are used by this model to share the electrons and hence to form the bonds. 

Discuss the nature of the bonding in the nitrate ion (NO3). Draw the possible Lewis resonance diagrams for this ion. Use the VSEPR theory to determine the steric numbeg the hybridization of the central N atom, and the geometry of the ion. Show how the use of resonance structures can be avoided by introducing a de-localized 77 MO. What bond order is predicted by the MO model for the N—O bonds in the nitrate ion ... 

The most intensely studied aldol addition mechanisms are those beUeved to proceed through closed transition structures, which are best understood within the Zimmerman-Traxler paradigm (Fig. 5) [Id]. Superposition of this construct on the Felkin-Ahn model for carbonyl addition reactions allows for the construction of transition-state models impressive in their abiUty to account for many of the stereochemical features of aldol additions [50a, 50b, 50c, 51]. Moreover, consideration of dipole effects along with remote non-bonding interactions in the transition-state have imparted additional sophistication to the analysis of this reaction and provide a bedrock of information that may be integrated into the further development and refinement of the corresponding catalytic processes [52a, 52b]. One of the most powerful features of the Zimmerman-Traxler model in its application to diastereoselective additions of chiral enolates to aldehydes is the correlation of enolate geometry (Z- versus E-) with simple di-astereoselectivity in the products syn versus anti). Consequently, the analyses of catalytic, enantioselective variants that display such stereospecificity often invoke closed, cyclic structures. Further studies of these systems are warranted, since it is not clear to what extent such models, which have evolved in the context of diastereoselective aldol additions via chiral auxiliary control, are applicable in the Lewis acid-catalyzed addition of enol silanes and aldehydes. 

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