Water is a transparent, odorless,
tasteless liquid. It illustrates 3 states of matter in the form of
ice, steam, and water. The form it takes depends on the temperature.
At low temperatures, the molecules do not move around as much and
form a crystalline structure that is rigid, and a little larger structure
in the liquid state, and very open in the gaseous state.
Water has a very large heat capacity, meaning
that it can absorb a great deal of heat without becoming extremely hot.
This fact makes the ocean a large reservoir of heat, that greatly affects
the overall weather and climate patterns of the world.
The students should remember from last week,
that the hydrogen and oxygen "bond" together, or "hold hands." The
bond is very strong and is called a covalent bond. Because the bond is
so strong, water is considered a universal solvent, since many things dissolve
in it. Water is a special type of covalent bond called a hydrogen bond.
Salts on the other hand hold hands very weakly and break up very easily
in water. This is called an ionic bond.
The break up of salts in water causes the
water to have the ions of that salt. For instance, table salt
is sodium chloride (NaCl). When it is dissolved in water it turns
into a positive ion of sodium (Na+) and a negative ion of chlorine (Cl-).
Dissolving does not mean that the compound breaks into its elements.
If that was the case, sodium, the element is reactive with water and chlorine
is a deadly gas. It is important to use the correct terms early in
a studentís education, so they don't get confused later on.
- Introduce the term ionic and
covalent bonding as a way that different compounds are held together. Ionic
bonds are not as strong as covalent. On the worksheet have students write a
sentence that covalent is a strong bond and ionic is weak or not as strong.
You might want them to think of a "poetic" way of writing it.
"Water is held together by very strong glue." "Salts are weak,
so they break apart easy."
- On the worksheet have them draw a
water molecule after you go over the water molecule pictured below.