1.  21.1 Water  21.2 Solutions  21.3 Acids, Bases, and pH

2.  We live on a watery planet.  All life on Earth depends on this combination of hydrogen and oxygen atoms.  What are the properties of water that make it so valuable?

3.  When two hydrogen atoms each share one electron with an oxygen atom, a neutral molecule is formed.

4.  Because negative charges repel, the electrons pairs around the oxygen atom are located where they are the farthest apart.  This results in a geometric shape called a tetrahedron.

5.  A water molecule has a negative end (pole) and a positive end.  A molecule (like water) with a charge separation is called a polar molecule.

6.  Ammonia, NH 3, is another polar molecule. With one lone pair and three bonding pairs of electrons.  This gives the ammonia molecule a pyramid shape.

7.  Methane, CH 4, is a nonpolar molecule.  Since there are no lone pairs of electrons, the electrons are shared equally between atoms.

8.  A hydrogen bond is a bond between the hydrogen on one molecule to another atom on another molecule.  Hydrogen bonds are relatively weak so they constantly break and re-form.

9.  Frozen water (or ice) has an organized structure that resembles a honeycomb because each water molecule can form hydrogen bonds with four other water molecules.

10.  The attraction between water molecules, called Cohesion, helps water travel from roots to stems and leaves.

11.  Water has a high specific heat value because of hydrogen bonds.  In order for water to boil, enough energy must be added to separate the hydrogen bonds.

12.  Water dissolves sodium chloride (salt) to form a solution of sodium (+) and chlorine (-) ions. Called dissosociation.

13. As water molecules collide with sugar crystals, attractions develop between the water molecules and sugar molecules at the surface of the solid. Dissolving

14.  In general, like dissolves like: ◦ water dissolves polar substances ◦ non-polar solvents dissolve non-polar substances