3. What causes hydrogen bonding?

Hydrogen bonding occurs between a hydrogen atom and an electronegative atom (e. g., oxygen, fluorine, chlorine). The bond is weaker than an ionic bond or a covalent bond, but stronger than van der Waals forces (5 to 30 kJ/mol). A hydrogen bond is classified as a type of weak chemical bond.

The variation in attraction of some atoms causes hydrogen bonding

Explanation:

Hydrogen bonding is caused by the tendency of some atoms in molecules to attract electrons more than their accompanying atom.

This gives the molecule a permanent dipole moment, it makes it polar, so it acts like a magnet and attracts the opposite end of other polar molecules.

What is hydrogen bonding?

A hydrogen bond is a partial intermolecular bonding interaction between a lone pair on an electron rich donor atom.