Why is hydrogen bind stronger than van der waals bond?
Answers
When a molecule containing a H atom is linked to a highly electronegative atom (like N, O, F), this atom attracts the shared pair of electrons more and so this end of the molecule becomes slightly negative while the other end (i.e., H-end) becomes slightly positive. The negative pole of one molecule attracts the positive pole of the other molecule and so on and as a result, a weaker bond is formed between them. This bond is called hydrogen bond.
As a result of Hydrogen bonding, a H-atom links the two electronegative atoms simultaneously, one by a covalent bond and the other by a hydrogen bond. Hence it is said to form a hydrogen bridge. Hydrogen bond is a weak bond, but it is stronger than van-der Waals forces.
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Vand der val's force of attraction is like a magnet attracting an iron nail and This force is not in contact with the other body, But the electron which is shared by H is physically connected, Thus it forms stronger bonds and Van der val's force forms less stronger bonds.
Eg: The graphite which is used in pencils, Graphite is used because it prints on the page easily and it's made of C-C layers which are attracted by Van Der Val's force of attraction. (This shows how weak is the Van der val's force of attraction is)