1. Properties of Water Unit 1 Lesson 6

2. Students will be able to:
Properties of Water
Students will be able to:
Identify the importance of water.
Identify the bonds between water atoms and molecules.
Explain the abnormality of some properties of water.
Explain why water is neutral.
Key Vocabulary:
Hydrogen bonds, covalent bonds, universal solvent, polar, partial charge, neutral effect, surface tension, latent heat, specific heat.

3. Can you imagine a world without water?
Properties of Water
Can you imagine a world without water?
No living organism can live without water even a single celled bacteria. The structure and function of living organisms depend mainly on water.
The human body is composed of water with percentage from 65% to 90%. We need water for digestion, respiration, maintaining our body temperature constant and keeping our bodies' internal environment healthy.

4. Properties of Water

5. Properties of Water
Water also constitutes more than 70% of the Earth's surface forming rivers, seas, lakes, oceans and underground water. From 50% to 80% of the life forms exist in the oceans and the oceans represent 97% of the total amount of water present on Earth.

6. Properties of Water
Structure of Water
Water exists in the three states; ice as solid, water as liquid and water vapor or steam as gas, under normal conditions.
The water molecule contains two hydrogen atoms and one oxygen atom, therefore, the chemical formula of water is H2O.
Each hydrogen atom bonds with the oxygen atom with a type of bond called covalent bond.
There is another type of bonds that exists between the water molecules called hydrogen bonds.

7. 1. Covalent bond in water molecules
Properties of Water
1. Covalent bond in water molecules
The oxygen atom shares one electron with each hydrogen atom and forms a single covalent bond, which results in an angle of 104.5o.
2. Hydrogen bonds between water molecules
The high difference between electronegativity between oxygen and hydrogen results in the formation of the hydrogen bonds.

8. Therefore, water is considered as a universal polar solvent.
Properties of Water
The electronegativity of oxygen is much higher than the electronegativity. This results in a high difference in electronegativity between oxygen and hydrogen in the molecule.
As a result, the oxygen acquires a partial negative charge and the hydrogen acquires a partial positive charge resulting in the polarity of the water molecules.
Therefore, water is considered as a universal polar solvent.

9. Properties of Water
Together, the hydrogen bond, the molecular geometry and the angle of the water molecule, and the polarity or the high difference in electronegativity in the water molecule are the main factors that are responsible for the unusual properties of water.

10. High boiling point and melting point
Properties of Water
High boiling point and melting point
According to the position of oxygen in group 16 of the periodic table, it was supposed that the boiling point of water is less than 100°C and the melting point is less than zero°C.
Compound
Boiling point
Melting point
Hydrogen Telluride
-4°C
-49°C
Hydrogen Selenide
-42°C
-64°C
Hydrogen Sulfide
-62°C
-84°C
Water
100°C
0°C

11. Properties of Water
The abnormality of the boiling point and melting point of water is due to the presence of hydrogen bonds.
The hydrogen bonds takes extra amount of heat energy to be broken first.
Then the molecules get more heat energy and increase the spaces between the water molecules and change from ice to water in melting process or from water to steam in boiling process.

12. 2. Water as a universal polar solvent
Properties of Water
2. Water as a universal polar solvent
If you get three empty beakers, add the same amounts of water in the three beakers, and then add table salt (NaCl) to the first beaker, sugar to the second beaker and oil to the third beaker, what will you observe?

13. In the first beaker, the table salt is dissolved in water.
Properties of Water
In the first beaker, the table salt is dissolved in water.
The reason for this is that the table salt molecules (NaCl) are polar molecules that contain positive Na ions and negative Cl ions.
That is, the water molecules are also polar molecules that contain partially positive H ions that attract the negative Cl ions, and partially negative OH ions that attract the positive Na ions.

14. Properties of Water
In the second beaker, the sugar is also dissolved in water, despite it is not a polar compound.
The sugar molecules dissolve in water due to the formation of hydrogen bonds between the water molecules and the sugar molecules.
In the third beaker, the oil fails to form either hydrogen bonds or electrostatic attraction force between positive and negative, therefore, it is not dissolved in water.

15. 3. Water has low density when it freezes
Properties of Water
3. Water has low density when it freezes
Any substance, even water, when they are cooled, their densities increase. So, when water is cooled, its density increases and ice is formed. But why can ice float on water?

16. Properties of Water
The density of water increases while cooling down until we reach 4°C. After 4°C, the density starts to decrease and ice floats on the surface of water.
The explanation of this is while freezing, molecules start to move slowly, making it easier for them to form hydrogen bonds.
Their crystalline shape now is open and hexagonal which increases their volume. The volume and density are inversely proportional. Therefore, the density decreases as the volume increases. And that's why a bottle of water may explode in freezer if it is full.

17. 4. Rising of latent heat, specific heat and surface tension
Properties of Water
4. Rising of latent heat, specific heat and surface tension
Rising of water latent heat, makes it resist the change from a state to another.
This property makes water one of the most important liquids used in fire extinguishing, as it consumes a large amount of heat of combustion media during its vaporization process.

18. Properties of Water
The high specific heat of water makes it absorb or lose a large amount of heat without changing its temperature therefore the temperature of human body doesn’t change by changing the atmospheric temperature.
The surface tension of water is high due to the hydrogen bonds between the molecules. This high surface tension is very important for the survival of some living organisms.

19. 5. Water has neutral effect on litmus paper and pH indicators
Properties of Water
5. Water has neutral effect on litmus paper and pH indicators
Water has a neutral effect on both blue and red litmus papers. This is because, when water is ionized, the positive H ions produced are equal to the negative OH ions. The pH of pure water is 7.

20. Summary Water is very important for all forms of life.
Properties of Water
Summary
Water is very important for all forms of life.
There are single covalent bonds inside the water molecules and hydrogen bonds between the water molecules.
These bonds are responsible for the unusual properties of water.
Water is a universal polar solvent.
Water has high boiling point and melting point.
Water has high specific heat capacity and latent heat.
Water has a neutral effect on litmus papers and pH indicators.