Why is water a polar molecule?
In this video, we'll explain simply why a water molecule is polar and it also has a bent shape.
Oxygen combines with 2 hydrogens in order to make 1 water molecule.
A water molecule, on the whole, is neutral. However, the electrons are not distributed evenly across the surface of the molecule and this causes the ends to be slightly charged.
- When oxygen bonds with hydrogen, oxygen attract electrons more strongly than hydrogen because of the higher electronegativity charge. The charge is caused by the protons - the positively charged protons in the nucleus attract the negatively charged electrons.
- Because of the stronger electronegative force in oxygen (oxygen has more protons than hydrogen), it causes the bonding pair of electrons to be held closer to the oxygen atom.
- The electrons are not equally shared and this results in oxygen having a slightly negative charge while the hydrogen has a slightly positive charge.
- This separation of charges is termed dipole moment.
Water has a bent shape
- The lone pair of electrons in the oxygen atom are not bonded to any atoms so they are free to repulse each other.
- These repulsive forces act to push the hydrogen atoms closer together and create a compression angle of 104º.
- Due to the special bent shape of the water molecule, this causes the water molecules to build crystal structure when water freezes.
- Hence water has a unique nature of expanding when it freezes.
- Please remember this is a 2D model and it does not represent how electrons are spread over a "volume" of space. The shape of the molecule is described as a "bent shape" but the electrons are tetrahedrally arranged.