Water molecules each consist of 1 oxygen (O) and 2 hydrogen (H) atoms.

O

H H

Figure 2.14 Water Molecules Surround Ions

The H2O molecule is asymmetrically constructed.

Figure 2.14 Water Molecules Surround Ions

Because of this asymmetry, there is a slight residual charge at both poles of the molecule.

The oxygen end retains a slight negative electrical charge...

and the hydrogen end retains a slight positive electrical charge.

-

+ +

Figure 2.14 Water Molecules Surround Ions

The ionic bonds between Na+ and Cl - hold the ions together in a solid crystal.

Figure 2.14 Water Molecules Surround Ions

However, when NaCl is dissolved in water...

Figure 2.14 Water Molecules Surround Ions

...the cation (Na+) attracts the negative

pole of water...

...and the anion (Cl-) attracts the positive

pole of water.

Figure 2.14 Water Molecules Surround Ions

Thus, the NaCl molecule dissolves.

Figure 2.14 Water Molecules Surround Ions

The dissolved ions are not able to reassociate into a solid.

Figure 2.14 Water Molecules Surround Ions