Question

Describe anomalous behavior of fluorine with the other elements of group 17 with reference to Hydrogen bonding.

Answer 1

Hint: We should know that Fluorine shows much anomalous behaviour compared to the other halogens present in its group. We would have to recall the reason for this behaviour to answer the question.

Complete step by step answer:
We must remember before proceeding that Fluorine is anomalous in various ways like, ionization enthalpy, electronegativity, enthalpy of bond dissociation which is higher than expected in comparison to the regular trends among the halogens. Its ionic and covalent radii, melting and boiling points, and electron gain enthalpy is also lower than expected in case of Fluorine.
There are many reasons as to why Fluorine is different from other halogens. The most significant of these are:
1. Fluorine has the smallest size among all group 17 elements.
2. Due to its small size, Fluorine also has the highest electronegativity among them all.
3. The F-F bond has a very low bond dissociation enthalpy.
4. There are no d- orbitals available in the valence shell of Fluorine as opposed to other halogens.

Coming to hydrogen bonding, Fluorine has the highest electronegativity among all halogens. This suggests that Fluorine forms strong hydrogen bonding with its hydrides unlike other group 17 elements as the H-F bond is extremely polar in nature. Thus hydrogen fluoride is liquid while other halides of hydrogen remain gaseous at room temperature. Thus, HF is also the weakest acid among all halogen acids since the H-F bond is extremely strong.

Note: We must note that HF cannot be stored in glass bottles unlike other hydrogen halides since it is very reactive and it reacts with silicates to form fluorosilicates.