Covalent Bonding Models and Reality

The Lewis model predicts the properties of molecular compounds in many ways. First, it accounts for why particular combinations of atoms form molecules and others do not. For example, why is water H2O and not HjO We can write a good Lewis structure for H2O, but not for H3O. 

In this way, the Lewis model predicts that H2O should be stable, while H3O should not be, and that is in fact the case. However, if we remove an electron from H3O, we get H30, which should be stable (according to the Lewis model) because, when we remove the extra electron, oxygen gets an octet. 

This ion, called the hydronium ion, is in fact stable in aqueous solutions (see Section 4.8). The Lewis model predicts other possible combinations for hydrogen and oxygen as well. For example, we can write a Lewis structure for H2O2 as follows  

Indeed, H2O2, or hydrogen peroxide, exists and is often used as a disinfectant and a bleach. 

A FIGURE 9.5 Intermolecular and Intramolecular Forces The covalent bonds between atoms of a molecule are much stronger than the interactions between molecules. To boil a molecular substance, you simply have to overcome the relatively weak intermolecular forces, so molecular compounds generally have low boiling points. 

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