FoundationalConceptsNeuroscience

to the rigid matrix of hydrogen bonds taking slightly more space than
when the molecules of water can slip and slide past one another in
their liquid state.
The polarity of water also accounts for water’s amazing ability to
dissolve many things, including ions. This can be illustrated by con-
sidering what is called table salt, sodium chloride (NaCl). A sodium
atom (Na), being from the left side of the periodic table, very readily
gives up an electron to form a positively charged sodium cation (Na’‘).
Achlorine atom, being from the right side of the periodic table, will
very readily take on an electron to form a negatively charged chloride
anion (CI). Crystalline table salt, sodium chloride, can be described as
an array of alternating sodium and chloride ions, held together by the
electrical attraction of their respective positive and negative charges.
In the absence of water, NaCl is an extremely stable structure. How-
ever, introduce even a small amount of water and the NaCl will begin
to dissolve, that is, fall apart into the water.
This illustrates water’s extraordinary ability to dissolve ions.
Because the charged ions are attracted to the opposite-charged
portions of the polar water molecule, water molecules can slip into
the otherwise very stable matrix of sodium and chloride forming
the salt crystal. As the salt crystal dissolves, the cations and anions
become surrounded with polar water molecules, attracted to the ionic
charges. A saltwater solution is formed. Water is very effective at
dissolving all kinds of atoms and molecules that have a net electrical
charge (such as ions) or, indeed, any polar molecule, because the pos-
itive and negative separation of charge in a polar molecule will be at-
tracted to the positive and negative separation of charge in the water
molecule.
This allows us to introduce a very important concept into our
description of solubility. Water, a polar molecule, dissolves (or loves