Shapes with More Than One Central Atom

Molecular Shapes with More Than One Central Atom 

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Shapes with More Than One Central Atom 10.3 Molecular Shape and Molecular Polarity... 

Shapes with Four Electron Groups Shapes with Five Electron Groups Shapes with Six Electron Groups Using VSEPR Theory to Determine Shape Shapes with More Than One Central Atom... 

So far we have discussed the geometry of molecules having only one central atom. The overall geometry of molecules with more than one central atom is difficult to define in most cases. Often we can only describe the shape around each of the central atoms. For example, consider methanol, CH3OH, whose Lewis structure is... 

The shapes of molecules with more than one central atom are composites of the shapes around each of the central atoms. Here are two examples ... 

Although many of the structures of interest to us have only one central atom, VSEPR theory can also be applied to molecules or polyatomic anions with more than one central atom. In such cases, the geometric distribution of terminal atoms around each central atom must be determined and the results then combined into a single description of the molecular shape. We use this idea in Example 10-12. 

Many molecules, especially those in living systems, have more than one central atom. The shapes of these molecules are combinations of the molecular shapes for each central atom. For these molecules, we find the molecular shape around one central atom at a time. Consider ethane (CH3CH3 molecular formula C2Hg), a component of natural gas (Figure 10.11 A). With four bonding groups and no lone pairs around each of the two central carbons, ethane is shaped like two overlapping tetrahedra... 

Figure 10.11 The tetrahedral centers of ethane and of ethanol. When a molecule has more than one central atom, the overall shape Is a composite of the shape around each center. A, Ethane s shape can be viewed as two overlapping tetrahedra. B, Ethanol s shape can be viewed as three overlapping tetrahedral arrangements, with the shape around the O atom bent (V shaped) because of its two lone pairs.

This example shows that a homonuclear polyatomic molecule (Os) can be polar shape is more important than differences in atoms and O, is polar despite all three atoms being oxygen. In this case, the central O atom has a different electron density associated with it than the outer two O atoms it is bonded to two O atoms whereas the outer atoms are bonded only to one O atom. 

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