Structure of a water molecule
A water molecule consists of one oxygen atom bonded to two hydrogen atoms. Each O–H bond is covalent, so the bonded atoms share electrons.
Oxygen pulls the shared electrons towards itself more strongly than hydrogen does. As a result, the charge within the molecule is not distributed equally.
- The region around oxygen carries a partial negative charge, δ−.
- The regions around the hydrogens carry partial positive charges, δ+.
The separation of these partial charges means that water is a polar molecule.
Link to hydrogen bonding
The differently charged regions of separate water molecules attract one another. A δ+ hydrogen region can be attracted towards the δ− oxygen region of a neighbouring molecule.
This intermolecular attraction allows hydrogen bonds to form between water molecules.
Exam Tip: To explain water's polarity, link the unequal sharing of electrons to the charges produced: oxygen becomes δ− while the hydrogen regions become δ+. Stating only that water has two charged ends is not enough.