Why is HF a stronger acid than hi?

I am a chemistry enthusiast with a passion for understanding the intricacies of chemical reactions and the properties of elements and compounds. One of the fascinating aspects of chemistry is the study of acids and bases, and how their properties vary across the periodic table.

Now, let's delve into the question of why hydrofluoric acid (HF) is a stronger acid than hydroiodic acid (HI). This is an interesting topic that involves understanding the concept of acid strength, which is influenced by several factors including the electronegativity of the halogen involved, the bond dissociation energy, and the molecular structure.

Firstly, electronegativity plays a crucial role in determining the strength of an acid. Electronegativity is the measure of an atom's ability to attract electrons towards itself in a chemical bond. Fluorine, being the most electronegative element, has a strong tendency to pull electrons towards itself when it forms a bond with hydrogen. This results in a polar bond, where the electron density is skewed towards the fluorine atom, leaving the hydrogen atom partially positive. This polarization facilitates the release of a proton (H+) from the acid, making HF a stronger acid.

Secondly, the bond dissociation energy is another factor that affects the acidity of hydrohalic acids. Bond dissociation energy is the energy required to break a chemical bond. The bond between hydrogen and fluorine in HF is weaker than that in HI due to the smaller size of fluorine compared to iodine. A weaker bond means less energy is required to break it, which in turn means that the acid can more readily donate a proton.

Thirdly, the molecular structure and the solvation of the acid in water also influence its strength. HF forms hydrogen bonds with water, which stabilizes the HF molecule and makes it more likely to donate a proton. On the other hand, HI, being a larger molecule, does not form hydrogen bonds as effectively with water, which makes it less likely to donate a proton.

It's important to note that while HF is a stronger acid than HI in terms of its ability to donate a proton, it is not the strongest hydrohalic acid. The strength of hydrohalic acids generally increases down the group in the periodic table, with HI being the strongest due to the increasing size and decreasing electronegativity of the halogens.

Now, let's address the statement provided for reference. It suggests that the charge is more stable on the larger atom, and thus HI is stronger than the other hydrohalic acids. However, this is not entirely accurate. While it is true that iodine is larger than fluorine, the strength of an acid is not solely determined by the size of the halogen. Electronegativity and bond dissociation energy are more critical in this context, and these factors favor HF over HI.

In conclusion, HF is a stronger acid than HI primarily due to the higher electronegativity of fluorine, the weaker bond between hydrogen and fluorine, and the ability of HF to form hydrogen bonds with water. These factors contribute to HF's greater tendency to donate a proton, which is the defining characteristic of an acid.

The charge is more stable on this larger atom. ... Iodine is so much bigger than fluorine that the charge is more stable on this larger atom. Thus, the trends for acidity of the hydrohalic acids are as follows: HI is strongest, followed by HBr, HCl, and finally HF.