Unit 9: Acids and Bases

What structural properties of a molecule cause it to behave as an acid or as a base? Well, any molecule containing a hydrogen atom is potentially an acid, but not all of them show acidic properties. So the main things that decide whether a molecule will behave as an acid is the strngth of the bond and the polarity of the bond.
These molecules can also just as well behave as a base if the hydroxide ion is produced instead of the hydrogen ion. This is dependant on the strength of the bonds electronegativity. When a covalent oxide dissolves in water, an acidic solution forms. These oxides are then called acidic oxides. Yet on the other hand, if basic solutions are produced it is called a basic oxide.

The Arrhenius concept was very useful but its use was very limited. It was then later replaced by the Lewis Acid-Base model. The Lewis Acid-Base Model viewed an acid as an electron pair acceptor and the base as a electron-pair donor. Another way to put this is that a Lewis acid has an empty atomic orbital that is can use to accept an electron. The Lewis acid accepts this electron from a molecule that has a lone pair of electrons, the Lewis Base. Note that the Bronsted-Lowry acid-base reaction is emcompassed in the Lewis model. The real value of the Lewis model for acids however is that it covers many reations that do not involve Bronsted-Lowry Acids, such as the gas-phase reaction between boron trifluoride and ammonia.
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