what is it

Hydrogen Bonding is an ionic interaction between a Polar Hydrogen and an Electronegative element.

Lets take two molecules of HF. Since F is highly electronegative, The bond pair lectrons drift a little to Florine side. This causes partial negative charge on F and partial positive charge on H. Same thing happens with other HF molecules.

Now, the partial positive H of 1 molecule is ionically attracted towards the Partial negative F of 2 molecule. This interaction is called hydrogen Bond.

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Hydrogen bond is defined as the electrostatic attraction between hydrogen atom and other atom with different electronegativity,i.e,,between H and F,O,N elements.e.g:HF-HF molecule has hydrogen bond with one H and other F.

                       H-F-----H-F-----H-F-----H-F-----H-F---