Joshua D. answered • 04/27/20
Programming and Machine Learning Tutor
To understand why water is polar, we first have to look at its valence shell electron repulsion theory (more commonly referred to as VSEPR) structure. In this case, water forms a bent structure in 3D space. Looking at this structure we can see the positively charged Hydrogen atoms are clustered closer together (due to the smaller angle between them of 104.5 as opposed to the 120 we would expect in an even distribution) while a section of the more negatively charged Oxygen molecule is more exposed. Despite having an overall neutral charge, depending on which side of the H2O molecule we are on in 3D space, it will either be more positive or more negative creating two distinct regions.
By definition, a polar molecule must have polar bonds due to a high electromagnetically differences between molecules, which water satisfies with its polar-covalent bond (3.44 O - 2.20 H), as well as having a dipole moment with two distinct regions of positive and negative charge, we we can clearly see in H2O's structure. This separation of charge is what makes water a polar molecule and useful solvent.
