Insulin is a complicated molecule called a protein. We will later consider simplier ways to consider the complicated molecules of life. Ions- atoms can obtain a stable number of electrons by giving up or gaining electrons. The ion pair is held together by strong electrostatic attractions. In water, two hydrogen atoms are covalently linked to one oxygen atom.
Oxygen is electronegative, or strongly electron attracting.
The hydrogen atoms are angled to one side of the oxygen. Thus, the electrons are more dense near the oxygen creating a partial negative charge. The two hydrogens have a partial positive charge, and the molecule is said to be polar. The electrostatic attraction between these charges leads to the formation of a hydrogen bond. The ability of ions and other molecules to dissolve in water is due to polarity.