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According to NCERT class 12 part 2, $\ce{ICl}$ has lesser bond enthalpy than $\ce{I2}$. I have read that non polar covalent bonds are weaker than polar covalent bonds as in polar covalent bonds partial opposite charges develop on the bonding elements which leads to extra electrostatic interaction between them which is absent in non polar bonds. So according to what I read the answer should have been opposite. Please let me know where this logic is wrong. Also using this logic I understood that ionic bond is stronger than covalent bond.

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    $\begingroup$ Do not generalize too much.At the end the polar character of a bond is an intrinsic result and not something that is formed after or on top of a preexisting bond. Size and shape of the bond matter, too. Note that I and Cl are both halogens so ICl isn't much polar. The same is true for the final statement. Ionic bond are very strong and easily the covalent ones can be much weaker - at least in vacuum! $\endgroup$ – Alchimista Nov 24 '18 at 12:12
  • $\begingroup$ @Alchimista My book says the order of bond strength of O-Cl< O-Br <O-I so as to explain the oxidising power of hypohalous acid (as the ease of releasing oxygen) HOCl>HOBr>HOI but according to you should it not be like just the reverse as 2p-3p overlap is stronger than 2p-4p which is stronger than 2p-5p. Is wrong reason given in my book if yes then how will you relate oxidising power of hypohalous acid? $\endgroup$ – Jasmine Nov 28 '18 at 0:44
  • $\begingroup$ Now Jasmine I do not see the answer in a quick. Still take what the book say. You take all given order or label as absolute... Do not do that. I didn't say what you claim. It would be a mixture of electronegativity and geometry. You should post a specific qusr $\endgroup$ – Alchimista Nov 30 '18 at 16:15
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In polar covalent bonds, say $A–X$, assume electronegativity of $X$ is greater than that of $A$ then their is polarisation of bond $A–X$, $X$ gains partial negative charge $\delta–$ and $A$ gains partial positive charge $\delta+$ but this charge is very less (as electrons of sigma bond are held tightly) to account for any significant increase in bond strength of $A–X$ bond but the $–X$ group in $A–X$ molecule tends to attract $A–$ group of another $A–X$ molecule in this way there is electrostatic interaction between two different $A–X$ molecules giving rise to intermolecular forces (Dipole-Dipole interaction, hydrogen bonding etc).

DO NOT CONFUSE FORCES BETWEEN TWO DIFFERENT MOLECULES AND COVALENT BONDS WHICH EXIST IN A SINGLE MOLECULE. THEY ARE TWO COMPLETELY DIFFERENT THINGS

However, attraction or repulsion may exist between two parts of a single molecule (generally happens for organic molecules) but doesn't significantly affects bond strength between them rather they tends to change orientation of those groups or may rotate about the sigma bond.

And for $ICl$ and $I_2$, bond of iodine and chlorine is weak due to polarisation. And bond between iodine and iodine is strong covalent bond. I hope you know that polarisation of electron cloud of sigma bond decrease overlapping between orbitals.

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