Properties of Water - Part I
CLASS SET DO NOT WRITE ON THIS
Why? When you hear that NASA’s space probes are looking for “evidence of life” on other planets, do you
know what that means? They are looking for evidence of liquid water. Water is fundamental for all life;
without it every living thing would die. Water covers about 70% of Earth’s surface and it makes up 6575% of our bodies (82% of our blood is water). Water has amazing properties that make it necessary for
supporting life.
MODEL 1: The structure of water
Directions: Use Model #1 to answer the question 1-7. Answer the questions in complete sentences.
1. Cut out your copy of Model #1, and paste it into your lab notebook.
2. How many Hydrogen atoms are there in water?
3. How many Oxygen atoms are there in water?
4. What holds the hydrogen atoms to the oxygen atom?
Read This! Electrons are negatively charged particles that help make up atoms. The shading
around the molecule represents the relative density of electrons shared by the atoms. The darker the
shading, the higher the density of electrons.
5. Around which atom is the shading darker? Around which atom is the shading lighter?
6. Which atom has more negative charge? Which atom has more positive charge?
7. Where is the majority of negative charge in a water molecule?
Directions: Cut out your copy of Model #2 and paste it into your lab notebook. Use it to answer questions
# 8 -15. Answer the questions in complete sentences.
Weak electrostatic attractive force
8. Tell what atoms are represented by the small, unshaded circles in Model 2.
9. Tell what atoms are represented by the large, grey shaded circles in Model 2.
10. What do the solid lines between the small and large circles represent?
11. According to Model #2, what is represented by the dotted lines?
12. Remember that the negative electrons are denser around the oxygen atoms and less dense around the
hydrogen atoms.
a. What kind of charge does the oxygen atom have compared to the hydrogen atom?
b. What kind of charge does the hydrogen atom have compared to the oxygen atom?
13. The Greek symbol  (delta) means partial.
a. The oxygen atoms in water have a partial negative charge, written -. On model #2, label each
oxygen with its partial charge.
b. The hydrogen atoms in water have a partial positive charge, written +. On model #2, label
each hydrogen its partial charge.
14. Describe the arrangement of the water molecules in Model 2 with one another. Look at the where they
hydrogens and oxygens are….
15. Describe the cause of the attractions between molecules of water. Make sure to use the word “charge”
in your answer.
16. Add another water molecule to the group in Model 2 at the upper right side. Which of its atoms
needs to connect to the existing molecule using a dotted line? Describe your reasoning.
17. Cut out your picture of three water molecules and paste it into your lab notebook. Draw 10 more water
molecules to create a cluster. Be sure to indicate the electrostatic attractive forces between
molecules that make water sticky.
Properties of Water – Part II
Directions: Copy Model #3 into your notebook. Use it to answer questions 1Model # 3: Sodium and Chlorine ion.
Na+1
1.
Cl-1
Model #3 shows two ions. From the model, are ions neutrally charged or do they have charge?
2.
What is the charge for sodium ion?
3.
What is the charge for chloride ion?
4.
Sodium ion is called a cation. Mg+2 is also a cation. Are cations positive or negative?
5.
Chloride ion is called a anion. F-1 is also an anion. Are anions positive or negative?
6.
Do you think these two ions would attract each other or repel each other?
7.
NaCl is formed by an ionic bond. Looking at model #3, what is your definition of ionic bond?
READ THIS: When NaCl is put in water, it will dissolve. When it dissolves, the sodium and the chlorine
separate into two charged atoms, called ions. This means that the sodium has a positive charge, +1, and
is called sodium ion. The chlorine a negative charge and is called chloride ion, -1.
8. You will need 3-D water molecules for the questions 8a- 8d.
a. Arrange your water models around the positive Na+1 ion. Sketch your arrangement. In your
sketch make sure to include the charge on the ion and to label the partial charges on the water
models.
b. Did you place the place the oxygen atom or the hydrogen atoms next to your ion? Explain.
c. Arrange your water models around the negative Cl -1 ion. Sketch your arrangement. In your
sketch make sure to include the charge on the ion and to label the partial charges on the water
models.
d. Did you place the place the oxygen atom or the hydrogen atoms next to your ion? Explain.
9. Do you think the attraction between water and Na+1 is stronger or the attraction between water and
water is stronger? Explain.
10. Predict which would have stronger surface tension, water or water contaminated NaCl? In other words,
which is stickier?
Read This! The main ingredient in soap is a very long molecule. Part of the soap molecule is neutral and
has no charge. The neutral part cannot form strong attractive forces with water. Part of the soap molecule
is negatively charged and will mix with water.
Model 4: A soap molecule written two ways.
Directions: Cut our version of Model #4 and paste it into your lab notebook. Use it to answer questions
11-14.
11. The soap molecules represented in Model #4 are the same, but written two different ways. In the top
model, what does each “bend” or “angle” in the line represent?
12. The charge on a soap molecule is concentrated around the oxygens. Circle that part of the molecule.
Is the charge around the oxygens positive or negative?
13. The carbon and hydrogen chain of the soap molecule is neutral. Circle that part of the molecule. What
charge does that part of the molecule have?
14. Predict which part of the soap molecule will form strong attractive forces with water molecules?
Explain.
Model 5: A soap bubble
Directions
1. In the soap bubble, where are the water molecules located?
2. In the soap bubbles, are the water molecules next to the partially negative charged part of the
soap molecule or next to the neutral charged part of the soap molecule?
3. Dirt and grime are mostly made up of neutral charged particles. What part of the soap bubble is
neutrally charged?
4. In what part of the soap bubble does the dirt and grime get trapped?
5. What happens to the attractive forces between water molecules if there are a lot of soap bubbles
floating around? Are there more/less attractive forces?