For X2O, swapping -H for -Cl drops the boiling point by 98 degree C. Specificall

Question

For X2O, swapping -H for -Cl drops the boiling point by 98 degree C. Specifically, water boils at 100 degree C, while CI2O boils at 2 degree C. Making reference to the relative contribution of all three types of non-covalent intermolecular forces, explain this difference in boiling point. In stark contrast, for NX3, swapping -H for -Cl raises the boiling point by over 100 degree C! That is, NH3 boils at -33 degree C, while NCI3 boils at +71 degree C. Why would the effect be exactly opposite? Make reference again to all three types of IMF's.

Explanation / Answer

a) H2O has strong hydrogen bonding as intermolecular forces where as Cl2O has only dipole-dipole interactions. In general dipole-dipole interactions are weaker than hydrogen bonding.

If the intermolecular attraction forces are strong then the compound has greater melting boiling points .

Hence H2O has higher boiling point than Cl2O.

b) NCl3 has greater dipolemomentum than NH3 so it has stronger intermolecular forces than NH3 and NCl3 has greater boiling point than NH3.

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