Shanxian Chemical
SUPPLEMENTS
Acidity of Hydrogen Halides
Research on the acidity of hydrogen halide
The acidity of hydrogen halide has been explored by the academic community for a long time. To understand, we should study its structure and properties in detail.
Hydrogen fluoride ($HF $), the intermolecular hydrogen bond is significant. The force of this hydrogen bond makes hydrofluoric acid in aqueous solution more difficult to dissociate hydrogen ions. Although fluorine is extremely electronegative, it is bound by hydrogen bonds, resulting in its weakest acidity in hydrogen halide. Looking at its ionization equilibrium: $HF\ rightleftharpoons H ^ {+} + F ^ {-} $, the equilibrium constant is small, due to hydrogen bonds.
As for hydrogen chloride ($HCl $), hydrogen bromide ($HBr $) and hydrogen iodide ($HI $), the intermolecular hydrogen bonds can be slightly weak. The three are almost completely ionized in water, and they are all strong acids. However, the acidity is still different. With the increase of the atomic number of halogen, the atomic radius increases, the bond length of $H-X $ ($X $is a halogen atom) increases, and the bond energy decreases. For example, the $H-Cl $bond of $HCl $is shorter and more energetic than the $H-Br $and $H-I $bonds. Therefore, the H-I bond of HI is the most easily broken, and hydrogen ions are most easily released in aqueous solution, and the acidity is the strongest; HBr is the second; HCl is the second.
In summary, the acidity of hydrogen halide is the weakest, and HI > HBr > HCl. The reason for this is the interaction of bond length, bond energy and hydrogen bond in molecular structure. When scholars understand this, they can be compared to chemistry.
The acidity of hydrogen halide has been explored by the academic community for a long time. To understand, we should study its structure and properties in detail.
Hydrogen fluoride ($HF $), the intermolecular hydrogen bond is significant. The force of this hydrogen bond makes hydrofluoric acid in aqueous solution more difficult to dissociate hydrogen ions. Although fluorine is extremely electronegative, it is bound by hydrogen bonds, resulting in its weakest acidity in hydrogen halide. Looking at its ionization equilibrium: $HF\ rightleftharpoons H ^ {+} + F ^ {-} $, the equilibrium constant is small, due to hydrogen bonds.
As for hydrogen chloride ($HCl $), hydrogen bromide ($HBr $) and hydrogen iodide ($HI $), the intermolecular hydrogen bonds can be slightly weak. The three are almost completely ionized in water, and they are all strong acids. However, the acidity is still different. With the increase of the atomic number of halogen, the atomic radius increases, the bond length of $H-X $ ($X $is a halogen atom) increases, and the bond energy decreases. For example, the $H-Cl $bond of $HCl $is shorter and more energetic than the $H-Br $and $H-I $bonds. Therefore, the H-I bond of HI is the most easily broken, and hydrogen ions are most easily released in aqueous solution, and the acidity is the strongest; HBr is the second; HCl is the second.
In summary, the acidity of hydrogen halide is the weakest, and HI > HBr > HCl. The reason for this is the interaction of bond length, bond energy and hydrogen bond in molecular structure. When scholars understand this, they can be compared to chemistry.
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