Each molecule has a net molecular dipole moment that is generated due to the fact that the dipole moments of the bonds do not cancel each other out. This molecular dipole moment makes each molecular dipolar possessing a positive end and a negative end to the molecule. If the molecules are small enough, polar water molecules can line up around the polar molecular substance with the positive end of water molecules attracted to the negative ends of the polar molecules and the negative ends of water molecules attracted toward the positive ends of the polar molecules. This force may overcome the dissociation energy of a bond within the polar molecule. If this should happen then the polar molecule will fragment with the broken bonding electrons going with the most electronegative atom in the broken bond.
Electronegativity is the electron attracting ability of an atom.
This will result in the creation of ions where no ions existed initially. Such polar molecular compounds are called electrolytes. If the bonds within the molecule are easier to break by the water molecules then the degree of ionization will be greater. More electrical current will be conducted. These are referred to as strong electrolytes.