chapter3 - Chapter 3 3.1 Lewis structures and VSEPR theory?...

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Unformatted text preview: Chapter 3 3.1 Lewis structures and VSEPR theory? (a) GeC1 3 ? Only one resonance structure is important (each atom has an octet). (b) FC0 2- ? W ith two resonance contributors to account for the equivalence of the two C-O bonds. Each atom has an octet. (c) C0 3 2- ? Three resonance structures are necessary to account for the fact that the three C-O bonds in the carbonate anion are equivalent, and these are shown below. Each atom has an octet in all three resonance structures. d) AlCl 4- ? Only one resonance structure is necessary to achieve an octet around each atom and to account for the equivalence of the four Al-Cl bonds, and it is shown below. (e) FNO? The least electronegative atom is likely to be the central atom. The Lewis structure of this molecule is shown above, requiring only one resonance structure to achieve an octet around all three atoms. 3.2 Lewis structures and formal charges? (a) ONC- ? With one O atom, one N atom, one C atom, and a -1 charge, the ONC anion has 16 valence electrons. You can arrange them in two resonance forms as follows: The nonzero formal charges for the atoms are given. These were calculated using the formula in Section 3.1(b), Formal charges. The number of lone pair electrons (not the number of lone pairs) and half the number of shared electrons are subtracted from the number of valence electrons on the parent atom. The resonance structure on the left is likely to be the dominant one, since it contains smaller formal charges. In addition, the resonance structure on the right is probably not very important because it puts a high negative formal charge on the least electronegative atom. (b) NCO? This ion also has 16 electrons, and the two most important resonance structures are shown below. The nonzero formal charges are given. The resonance structure on the left is likely to be the dominant one, since it puts the negative formal charge on 0, the most electronegative atom. 3.3 Formal charges and oxidation numbers of N0 2 ? The resonance structures, nonzero formal charges, and oxidation numbers for nitrite ion are shown below: The two structures shown are similar in that they both contain a N-O single bond and a N=O double bond. Therefore, they each contribute equally. The nitrogen atom in nitrite ion can be oxidized or reduced, since it is in the +3 oxidation state and since nitrogen can have oxidation numbers that range from -3 to +5. Both the oxidation number (+3) and the formal charge (0) on the nitrogen atom fail to give an accurate picture of its actual charge, which is slightly negative (that is, the negative charge is shared by all three atoms). 3.4 More Lewis structures? (a) XeF 4 ? There is a straight-forward way to draw Lewis F structures with a central atom and some number of atoms. In this case, start with the Lewis structure of a xenon atom. Then consider how many fluorine atoms there are in the molecule, and use one of xenons electrons for each Xe-F bond. The complete Lewis structure of XeF 4 is shown below. is shown below....
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chapter3 - Chapter 3 3.1 Lewis structures and VSEPR theory?...

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