Water is polar because oxygen attracts the shared electrons in each OtoH bond more strongly than hydrogen does, and the bent shape of the water molecule prevents the bond dipoles from cancelling. This gives oxygen a partial negative charge and the hydrogen atoms partial positive charges.
The mechanism
In a water molecule, , each hydrogen atom is joined to oxygen by a polar covalent bond. The electrons are shared, but not equally, because oxygen has a higher electronegativity than hydrogen-it attracts bonding electrons more strongly.
The shared electrons therefore spend more time near oxygen. Oxygen develops a partial negative charge, written δ−, while each hydrogen develops a partial positive charge, written δ+.
Water’s molecular shape is also essential. The molecule is bent rather than linear, so the two OtoH bond dipoles point in different directions and do not cancel. Their combined effect produces an overall molecular dipole, making water a polar molecule.
This polarity allows the δ+ hydrogen of one water molecule to attract the δ− oxygen of another. This intermolecular attraction is a . Hydrogen bonding explains important biological properties of water, including cohesion, adhesion, high specific heat capacity and its ability to dissolve many ionic and polar substances.
