Hydrogen bonds are weak attractions between atoms that have formed other chemical bonds. One of these atoms is electronegative, like oxygen, and has a partial negative charge. The other is a hydrogen atom that has bonded with another electronegative atom and has a partial positive charge.
Because hydrogen has very weak electronegativity when it binds with a strongly electronegative atom, such as oxygen or nitrogen, electrons in the bond are unequally shared. The other atom pulls the electrons to itself, sharing them with the hydrogen atom a smaller amount of the time. This gives the hydrogen atom a partial positive charge, causing it to be attracted to atoms with a partial negative charge. The cumulative effect of these weak attractions is life-altering, endowing water with high heat capacity, high heat of vaporization, ability to dissolve polar molecules, adhesion, cohesion, and strong surface tension.
