Why is the bond length of HI longer than that of HCl?

[elemis]

Click http://www.xtremepapers.net/CIE/International A And AS Level/9701 - Chemistry/9701_s02_qp_1.pdf" for question.

Question 33.

The atomic Radii of Iodine is much larger than Chlorine hence the bond length of HI should be smaller compared to HCl.

Apparently, it is not so, why ? It is actually the other way around.

Apparently options 2 and 3 are correct.

 

[dorebase2006]

Why did you think that the larger atomic radius of iodine makes the bond length of HI smaller? Correct me if I'm wrong but it's pretty common sense that the larger the atomic radius, the longer the bond length. Besides, due to the smaller electronegativity of iodine, H-I bond is not as polar as H-Cl and therefore less electrostatic attraction due to partial charges is experienced by H and I, thus they are further apart, increasing the bond length.

 

[elemis]

Why did you think that the larger atomic radius of iodine makes the bond length of HI smaller? Correct me if I'm wrong but it's pretty common sense that the larger the atomic radius, the longer the bond length. Besides, due to the smaller electronegativity of iodine, H-I bond is not as polar as H-Cl and therefore less electrostatic attraction due to partial charges is experienced by H and I, thus they are further apart, increasing the bond length.

I was exploring other avenues of thought ;)

Thanks for the explanation.