Arrange each group of compounds in order of decreasing acid...

Arrange each group of compounds in order of decreasing acid strength. Explain your reasoning. $\begin{array}{ll}{\text { (a) } \mathrm{H}_{2} \mathrm{O}, \mathrm{H}_{2} \mathrm{S}, \mathrm{H}_{2} \mathrm{Se}} & {\text { (b) } \mathrm{HClO}_{3}, \mathrm{HBrO}_{3}, \mathrm{HIO}_{3}} \\ {\text { (c) } \mathrm{PH}_{3}, \mathrm{H}_{2} \mathrm{S}, \mathrm{HCl}}\end{array}$

Arrange each group of compounds in order of decreasing acid strength. Explain your reasoning.
$\begin{array}{ll}{\text { (a) } \mathrm{H}_{2} \mathrm{O}, \mathrm{H}_{2} \mathrm{S}, \mathrm{H}_{2} \mathrm{Se}} & {\text { (b) } \mathrm{HClO}_{3}, \mathrm{HBrO}_{3}, \mathrm{HIO}_{3}} \\ {\text { (c) } \mathrm{PH}_{3}, \mathrm{H}_{2} \mathrm{S}, \mathrm{HCl}}\end{array}$

Key Concepts

Oxyacid Structure and Oxidation States

Oxyacids contain hydrogen, oxygen, and another element, where the acid strength is affected by the oxidation state of the central atom. A higher oxidation state typically pulls electron density away from the acidic hydrogen through an inductive effect, thereby stabilizing the conjugate base and increasing acid strength. Additionally, the number and arrangement of oxygen atoms can enhance this effect via resonance stabilization.

Electronegativity and Conjugate Base Stability

The electronegativity of the atom bonded to hydrogen plays a key role in acid strength. A more electronegative atom can better stabilize the negative charge on the conjugate base, resulting in a stronger acid. The balance between bond strength and electronegativity helps determine how readily an acid donates its proton.

Periodic Trends in Binary Hydrides

For acids made of hydrogen and a non-metal element (binary hydrides), acid strength is influenced by the size of the atom bonded to hydrogen. As atoms get larger down a group, the H–X bond becomes longer and weaker, making it easier to release the proton. This trend is observed among elements in the same group of the periodic table, leading to increased acid strength with increasing atomic size.

Acid Strength Fundamentals

Acid strength is determined by the tendency of the acid to donate a proton (H?) to a base. This tendency depends on factors like the bond strength between the hydrogen and the atom it is bonded to, the stability of the conjugate base once the proton is lost, and the overall electron distribution within the molecule.

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