Problem 59 - Chemistry: An Atoms-Focused Approach

Question

Draw Lewis structures that show how electron pairs move and bonds form and break during the autoionization of water. Label the appropriate \(\mathrm{H}_{2} \mathrm{O}\) molecules as the Lewis acid and Lewis base.

Step-by-Step Solution

Answer

Answer: In the autoionization process, one water molecule acts as a Lewis base, donating a hydrogen atom with its electron pair to the other water molecule, which acts as a Lewis acid. This process results in the formation of a hydronium ion (H₃O⁺) and a hydroxide ion (OH⁻).

Step 1: Draw the Lewis structure of a water molecule

To draw the Lewis structure of a water molecule (\(\mathrm{H}_{2} \mathrm{O}\)), first, arrange the atoms: the central atom (oxygen) is bonded to two hydrogen atoms. The oxygen atom has 6 valence electrons, and each hydrogen has 1 valence electron. Oxygen forms two single bonds with the hydrogen atoms, and it's left with two lone pairs of electrons. Lewis structure for water: O / \ H H

Step 2: Identify a molecule as a Lewis acid and another as a Lewis base

In autoionization, one water molecule will act as a Lewis acid by accepting an electron pair, and the other will act as a Lewis base by donating an electron pair. In this case, the oxygen atom of the Lewis acid molecule will accept the electron pair from a hydrogen atom of the Lewis base molecule.

Step 3: Draw the Lewis structures showing the movement of electron pairs and bonds formation and breakage during autoionization

During the autoionization process, the electron pair from an oxygen-hydrogen bond of one water molecule (Lewis base) is donated to the oxygen of another water molecule (Lewis acid), forming a hydronium ion (\(\mathrm{H}_{3} \mathrm{O}^{+}\)) and a hydroxide ion (\(\mathrm{OH}^{-}\)). The Lewis structures showing this process are: Lewis base Lewis acid O O / \ / \ H H + H H |---| Movement: v Hydronium ion Hydroxide ion O O /|\ / \ H H H H ..

Step 4: Label the structures as Lewis acid and Lewis base

Now, we can label the water molecules as the Lewis acid and Lewis base in the initial reaction: Lewis base Lewis Acid O O / \ / \ H H + H H Overall, the autoionization process of water involves one water molecule acting as a Lewis base, donating a hydrogen atom with its electron pair to the other water molecule as a Lewis acid, resulting in the hydronium and hydroxide ions.