Resonance Lewis structure, writing

Write the Lewis structures, including resonance structures where appropriate, for (a) the oxalate ion, C2042- (there is a C—C bond with two oxygen atoms attached to each carbon atom) (b) BrO+ (c) the acetylide ion, C22-. Assign formal charges to each atom. 

The double arrow indicates that these Lewis structures are resonance forms. It does not mean that the molecule vibrates back and forth between these two forms but rather that there is just one form of ozone. The reason for writing the two structures is that there is a limitation in the ability of Lewis structures to describe the electron distribution in some molecules. 

PROBLEM 1.19 Write Lewis structures and resonance forms for the following compounds. If you have problems visualizing the structure of some of these molecules, see the inside front cover of this book. 

It IS good chemical practice to represent molecules by their most stable Lewis structure The ability to write alternative resonance forms and to compare their relative stabilities however can provide insight into both molecular structure and chemical behavior This will become particularly apparent m the last two thirds of this text where the resonance concept will be used regularly... 

Resonance can be anticipated when it is possible to write two or more Lewis structures that are about equally plausible. In the case of the nitrate ion, the three structures we have written are equivalent. One could, in principle, write many other structures, but none of them would put eight electrons around each atom. 

Strategy Write a Lewis structure for the N02 ion, following the usual steps. Then write the other resonance form by changing the position of the multiple bond. Do not change the skeleton structure. 

Lewis structure An electronic structure of a molecule or ion in which electrons are shown by dashes or dots (electron pairs), 166-167,192q formal charge, 171-172 nonmetal oxides, 564-565 oxoacids, 567 resonance forms, 170-171 writing, 168-169 Libby, Willard, 174... 

STRATEGY Write a Lewis structure for the molecule by using the method outlined in Toolbox 2.1. Decide whether there is another equivalent structure that results from the interchange of a single bond and a double or triple bond. Write the actual structure as a resonance hybrid of these Lewis structures. 

Self-Test 2.7A Write Lewis structures contributing to the resonance hybrid for the acetate ion, CH ,CC)2. The structure of CH COOH is described in Example 2.4 the acetate ion has a similar structure, except that it has lost the final H atom while keeping both electrons from the O -H bond. 

Self-Test 2.7B Write Lewis structures contributing to the resonance hybrid for the nitrite ion, N02. ... 

Write the Lewis structures that contribute to the resonance hybrid of the guanadinium ion, C(NH2)3+. 

Write the Lewis structure, including typical contributions to the resonance structure (where appropriate, allow for the possibility of octet expansion, including double bonds in different positions), for (a) sulfite ion (b) hydrogen sulfite ion (c) perchlorate ion (d) nitrite ion. 

Self-Test 15.IB (a) Write the Lewis structure for the azide ion and assign formal charges to the atoms. (b)You will find it possible to write a number of Lewis structures. Which is likely to make the biggest contribution to the resonance ... 

Sometimes when writing the Lewis structure of a species, we may draw more than one possible correct Lewis structure for a molecule. The nitrate ion, N03 , is a good example. The structures that we write for this polyatomic anion differ in which oxygen has a double bond to the nitrogen. None of these three truly represents the actual structure of the nitrate ion—it is an average of all three of these Lewis structures. We use resonance theory to describe this situation. Resonance occurs when more than one Lewis structure (without moving atoms) is possible for a molecule. The individual structures are called resonance structures (or forms) and are written with a two-headed arrow (<- ) between them. The three resonance forms of the nitrate ion are ... 

Write all the possible Lewis structures for the nitrate ion (N03 ). Experimental data shows that the nitrate ion has three identical bonds. Show that the structures are resonance forms by the correct use of arrows. 

Resonance must be used whenever more than one reasonable Lewis structure can be written for a molecule, provided that the Lewis structures have identical positions of all atoms. Only the positions of unshared electrons and multiple bonds are changed in writing different resonance structures. When a better picture of bonding is developed in Chapter 3, we will get a better understanding of what resonance means and when it must be used. 

Write the Lewis structure(s). If there are resonance structures, pick any one. 

Write down the Lewis structure of the reactants, complete with formal charges, and draw any major resonance forms. Look for leaving groups, polarized single and multiple bonds, acids and bases. Classify into generic sources and sinks and then rank them. The reaction usually occurs between the best source and sink. Above all, note if the medium is acidic or basic. In basic media, find the best base, and then locate any acidic hydrogen within range (not more than 10 p Ta units above the pATabH of Ihe base). In acidic media, identify the best sites for protonation. Likewise, do not create a species that is more than 10 units more acidic than your acid. Understand what bonds have been made or broken, but do not lock into an arbitrary order as to which occurred first. 

Careful examination of the ozone molecule indicates that the two outer oxygens are the same distance from the central oxygen. Write Lewis formulas or resonance structures that are consistent with this finding. 

Write the Lewis structures of the three resonance forms of sulfur trioxide, S03, then combine them in a fourth composite structure showing the delocalization of the pair of electrons over all atoms in the molecule. 

Write Lewis structures for the following species, including all resonance forms, and show formal charges (a) HCO2, (b) CH2NO2. Relative positions of the atoms are as follows ... 

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