Ethene VSEPR

Ethyne, ethene and ethane contain 10. 12 and 14 valence electrons, respectively. They are isoelectronic with N2, 02 and F., respectively. Along both series of molecules the central link becomes progressively weaker and the bond lengths increase. The carbon-carbon bond length increases from 121 pm in ethyne to 133 pm in ethene and to 155 pm in ethane. The corresponding bond enthalpy terms are 837, 612 and 348 kJ mol Data for the diatomic molecules is contained in the text. Discuss these data in terms of the VSEPR and MO treatments of the molecules. 

Figure 3.13 also shows the structure for CH20. Because VSEPR theory predicts a trigonal planar geometry for the double bond and the two electron pairs on the oxygen, we will treat it as spr hybridized. Again, the picture is similar to ethene, with one CO sigma bond and one CO pi bond, but with both unshared electron pairs in... 

List all the symmetry elements of the molecules (a) BF3, (b) SF4 and (c) ethene, C2H4, and give them their correct symbols. (Use VSEPR theory to predict the shapes.)... 

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