Trigonal planar arrangement VSEPR

Ethylene is a planar molecule. The H—C—H and H—C—C bond angles are close to 120°. VSEPR theory treats each C atom as being surrounded by three electron groups in a trigonal-planar arrangement. VSEPR theory does not dictate that the two —CH2 groups be coplanar, but as we will see, valence bond theory does. 

Use the VSEPR model to identify The C atom is bonded to 3 atoms and has no lone the electron arrangements around pairs therefore, it has a trigonal planar arrangement,... 

Recall that in the VSEPR model a double bond acts as one effective pair. Thus in the ethylene molecule each carbon is surrounded by three effective pairs. This model requires a trigonal planar arrangement with bond angles of 120 degrees. What orbitals do the carbon atoms use in this molecule The molecular geometry requires a planar set of orbitals at angles of 120 degrees. Since... 

Solution There are three pairs of electrons around the C atom therefore, the electron pair arrangement is trigonal planar. (Recall that a double bond is treated as a single bond in the VSEPR model.) We conclude that C uses sp hybrid orbitals in bonding, because sp hybrid orbitals have a trigonal planar arrangement (see Table 10.4). We can imagine the hybridization processes for C and O as follows ... 

It has been found that when an optically active sample of a chiral tertiary halogenoalkane undergoes hydrolysis, all of the optical activity is lost. This observation is consistent with the suggested mechanism. VSEPR theory (Chapter 4) predicts that the three bonds from the positively charged carbon are in the form of a trigonal planar arrangement (Figure 20.77). 

Multiple bonds are treated as a single unit m the VSEPR model Formaldehyde is a trigonal planar molecule m which the electrons of the double bond and those of the two single bonds are maximally separated A linear arrangement of atoms m carbon diox ide allows the electrons m one double bond to be as far away as possible from the elec Irons m the other double bond... 

Valence shell electron-pair repulsion (VSEPR) model (Section 1.10) Method for predicting the shape of a molecule based on the notion that electron pairs surrounding a central atom repel one another. Four electron pairs will arrange themselves in a tetrahedral geometry, three will assume a trigonal planar geometry, and two electron pairs will adopt a linear arrangement. 

Because VSEPR treats double bonds as though they were single, the SO2 molecule can be viewed as consisting of three electron pairs on the central S atom. Of these, two are bonding pairs and one is a lone pair. In Table 10.1 we see that the overall arrangement of three electron pairs is trigonal planar. But because one of the electron pairs is a lone pair, the SO2 molecule has a bent shape. 

The C=C bond is treated as though it were a single bond in the VSEPR model. Because there are three electron pairs around each C atom and there are no lone pairs present, the arrangement around each C atom has a trigonal planar shape like BF3, discussed earlier. Thus, the predicted bond angles in C2H4 are... 

As you review each type of hybrid orbital in the following subsections, take note of (1) the number and types of atomic orbitals that were combined to make the hybrid orbitals, (2) the number of orbitals that remain uncombined, and (3) the three-dimensional arrangement in space of the hybrid orbitals and any uncombined p orbitals. In particular, you will find that these three-dimensional arrangements will retain the names (tetrahedral, trigonal planar, linear) and bond angles (109.5°, 120°, and 180°) used to describe the shapes of molecules in our section on VSEPR (Section 1.3). 

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