VSEPR model steps

Like so many other molecular properties, shape is determined by the electronic structure of the bonded atoms. The approximate shape of a molecule can often be predicted by using what is called the valence-shell electron-pair repulsion (VSEPR) model. Electrons in bonds and in lone pairs can be thought of as "charge clouds" that repel one another and stay as far apart as possible, thus causing molecules to assume specific shapes. There are only two steps to remember in applying the VSEPR method ... 

In the third step, the S03 is absorbed in concentrated sulfuric acid rather than in water because the dissolution of S03 in water is slow. Water is then added to achieve the desired concentration. Commercial concentrated sulfuric acid is 98% H2S04 by mass (18 M H2S04). Anhydrous (100%) H2S04 is a viscous, colorless liquid that freezes at 10.4°C and boils above 300°C. The H2S04 molecule is tetrahedral, as predicted by the VSEPR model (Section 7.9)... 

To see how the VSEPR model works, examine the methane (CH4) molecule. The first step is to write its Lewis structure. 

Before going on to discnss the hybridization of d orbitals, let ns specify what we need to know in order to apply hybridization to bonding in polyatomic molecnles in general. In essence, hybridization simply extends Lewis theory and the VSEPR model. To assign a snitable state of hybridization to the central atom in a molecnle, we must have some idea about the geometry of the molecule. The steps are as follows ... 

Steps for Predicting Molecular Structure Using the VSEPR Model... 

Recall that the main idea of the VSEPR model is to find the arrangement of electron pairs around the central atom that minimizes the repulsions. Then we can determine the molecular structure from knowing how the electron pairs are shared with the peripheral atoms. Use the following steps to predict the structure of a molecule using the VSEPR model. 

Thus CO2 has two "effective pairs" that lead to its linear structure, whereas O3 has three "effective pairs" that lead to its bent structure with a 120° bond angle. Therefore, to use the VSEPR model for molecules (or ions) that have double bonds, we use the same steps as those given in Section 12.9, but we count any double bond the same as a single electron pair. Although we have not shown it here, triple bonds also count as one repulsive unit in applying the VSEPR model. 

We can generalize the steps we follow in using the VSEPR model to predict the shapes of molecules or ions ... 

To predict the shapes of molecules with the VSEPR model, we use the following steps ... 

Step 2 From the Lewis formula, use the VSEPR model to obtain the arrangement of electron pairs about this atom. 

Steps to Apply the VSEPR Model 1 Draw the Lewis structure for the molecule. 

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