Question:

The correct order of the thermal stability of hydrogen halides (H-X) is

Updated On: Apr 15, 2024
  • HI > HCl < HF > HBr
  • HCl < HF > HBr < HI
  • HF > HCl > HBr > HI
  • HI < HBr > HCl < HF
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The Correct Option is C

Solution and Explanation

The H-X bond strength decreases from HF to HI. i.e. HF > HCl > HBr > HI. Thus HF is most stable while HI is least stable. The decreasing stability of the hydrogen halide is also reflected in the values of dissociation energy of the H-X bond
HFHClHBrHI135kcalmol1103kcalmol185kcalmol171kcalmol1\begin{matrix}H-F&H-Cl&H-Br&H-I\\ 135\,kcal\,mol ^{-1}&103\,kcal\,mol ^{-1}&85\,kcal\,mol ^{-1}&71\,kcal\,mol ^{-1}\end{matrix}
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Concepts Used:

Group 17 Elements

Halogens are the group 17 elements of the periodic table. The term ‘halogen’ means ‘salt-producing’, hence the name halogens as they possess the tendency to form salts after reacting to metals. It generally has five elements:

  • Fluorine (F)
  • Chlorine (Cl)
  • Bromine (Br)
  • Iodine (I)
  • Astatine (At)

These are all naturally occurring halogens but Tennessine (Ts) is an artificially created halogen.

Halogens:

Halogens are highly reactive elements and are highly electronegative. They have a high tendency to react with metals to form salts. They are also known as Group 17 elements. They have 7 electrons in their outer shell with a configuration of (ns2 np5). Fluorine being the first halogen in group 17, is highly reactive. Astatine is a halogen because of its resemblance with iodine despite it being radioactive.

Electronic Configuration:

The general electronic configuration for group 17 elements is ns2np5. This configuration clearly shows that they have 7 electrons in their valence shell. They require one more electron to complete their octet and achieve noble gas configuration.