Element 85, astatine (At), is a radioactive halogen that is...

Element $85,$ astatine $(\mathrm{At})$, is a radioactive halogen that is not present in appreciable amounts in nature. The acid HAt can be prepared and compared with the other hydrogen halides. Explain why you expect HAt to be stronger or weaker than HI.

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Key Concepts

Periodic Trends in Hydrogen Halides

In the hydrogen halides, acid strength generally increases as you move down the halogen group. This is mainly because as the size of the halogen increases, the H–X bond becomes longer and weaker, making proton donation easier. This trend helps predict the acid strength among different hydrogen halides.

Polarizability

Polarizability refers to the ease with which the electron cloud in a molecule can be distorted. In heavier halogens, higher polarizability leads to a weaker and more diffuse electron distribution around the atom, which can contribute to a weaker H–X bond. This makes the corresponding hydrogen halide a stronger acid because the proton is more readily dissociable.

Acid Strength

Acid strength refers to the tendency of an acid to donate a proton (H+). In hydrogen halides, the ease with which the H–X bond can be broken to release the proton is a key determinant of acid strength. If the bond is weaker, it is easier for the acid to lose the proton, resulting in a stronger acid.

Bond Dissociation Energy

Bond dissociation energy is the energy required to break a chemical bond. In the context of hydrogen halides, a lower bond dissociation energy for the H–X bond means the bond is easier to break, thereby increasing the acid's ability to release a proton and enhancing its acid strength.

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