Problem 65 - Chemistry An Atoms First Approach

Question

How does the oxyacid strength of the halogens vary as the number of oxygens in the formula increases?

Step-by-Step Solution

Answer

The strength of oxyacids of halogens generally increases as the number of oxygen atoms in the formula increases. This is due to increased electron delocalization over a larger number of oxygen atoms, which stabilizes the conjugate base formed upon the removal of the acidic hydrogen. For example, in the series of chloric acids, oxyacid strength increases in the order HOCl < HClO2 < HClO3 < HClO4 with increasing oxygen atoms.

Step 1: Understand oxyacids of halogens

Oxyacids are acids that contain an acidic hydrogen atom bonded to an oxygen atom. Oxyacids of halogens are a particular class of oxyacids in which the central atom is a halogen. The general form for a halogen oxyacid is HOX(O), where the 'X' represents the halogen element and the '(O)' represents the oxygen atoms surrounding the halogen. Examples of halogen oxyacids include hypochlorous acid (HOCl), chlorous Acid (HClO2), and chloric Acid (HClO3).

Step 2: Observe the effect of the electronegativity of halogens

Electronegativity is a key factor in determining oxyacid strength. In general, as the electronegativity of the central atom (in this case, the halogen) increases, the oxyacid strength also increases. This is because greater electronegativity allows the central atom to draw the bonding electrons closer, facilitating easier removal of a proton (H+) from the O-H bond, thus increasing the acidity.

Step 3: Analyze the impact of the number of oxygen atoms on oxyacid strength

As the number of oxygen atoms surrounding the central halogen atom increases, the oxyacid strength generally increases. This is due to increased electron delocalization over a larger number of oxygen atoms, which stabilizes the conjugate base formed upon the removal of the acidic hydrogen. This effect can be observed in the series of chloric acids: hypochlorous acid (HOCl) < chlorous acid (HClO2) < chloric acid (HClO3) < perchloric acid (HClO4). In this example, we can notice that as the number of oxygen atoms increases, the oxyacid strength also increases.

Step 4: Generalize the trend in oxyacid strength

To generalize this trend, we can conclude that in halogen oxyacids, as the number of oxygen atoms in the formula increases, so does the strength of the oxyacid. This is because the increased electron delocalization resulting from the additional oxygen atoms stabilizes the conjugate base, making the oxyacid compound more acidic.