Properties of Water

How would you describe water?

What we tend to describe it as... No color No taste No odor Plain, ordinary

Chemists think differently!

Some Properties of Water:

Water is made up of atoms. 2 hydrogen and 1 Oxygen atom form

a water molecule (H2O) Hydrogen = slight (+) or positive

charge Oxygen= slight (–) or negative

charge

Polar molecule= a molecule that has electrically charged areas. Substances with polar molecules are called polar substances.

Question: What kind of charges do the elements in water have?

Water is a polar molecule.

The positive hydrogen ends of one water molecule attract the negative oxygen ends of nearby water molecules. As a result, the water molecules tend to stick together.

Question: What makes water a polar molecule?

• Because it is a polar substance, water has many unusual properties:

Surface tension= the tightness across the surface of water that is caused by the polar molecules pulling on one another. The pulling forces the surface of the water into a curved shape. It also causes raindrops to form round beads when landing on a windshield of a car.

•Question: Why does water seem to have a “skin” on its surface?

How many drops of water can you put on a

penny????

Capillary Action= the combined force of attraction among water molecules and with the molecules of surrounding materials. Causes water molecules to cling to

the fibers of materials like paper and cloth

Allows water to move through materials with pores or narrow spaces inside

– Question: How does a paper – towel soak up water?

Capillary Action in Action! Teacher: you may want to skip ahead a little at a time. (4

min)

Solution= a mixture that forms when one substance dissolves another. (ex. Lemonade) The substance that does the dissolving is

called the solvent. (in this example= water)

– Solvent dissolves Solute (water is solvent and lemonade powder would be solute)

– Question: Give me another example of a solution. (not lemonade)

Water is often called the “universal solvent” because it dissolves so many substances because it is made up of polar molecules, which attract other substances with polar molecules. It can dissolve sugar, salt, soap, liquids

such as bleach and rubbing alcohol, and gases such as oxygen and carbon dioxide.

It cannot dissolve oils and wax because they are made up of non-polar molecules which do not dissolve well in water.

Question: Why is water called the universal solvent?

Water exists on Earth in all three states: solid, liquid and gas. The molecules in solid ice are close

together and form a rigid structure. (cold temperatures <0 degrees C)

In liquid water, the molecules move more freely and the water takes the shape of its container. (0 to 100 degrees C)

The molecules in gaseous water vapor move very freely and spread out to fill a space. (> 100 degrees C)

– Question: Describe the structureof molecules in liquid water.

Temperature is a measurement of the average speed of the molecules. Ice has the lowest temperature/speed and Gaseous water vapor has the highest.

Energy must be added or released for water molecules to change state: Evaporation is the process by which

molecules at the surface of a liquid absorb enough energy to change to the gaseous state.

Condensation is the process by which a gas changes to a liquid.

– Question: What is it called when water vapor in the air changes to a liquid on a glass?

When water cools below 4 degrees C the molecules begin to line up in a grid-like crystal structure which takes up more space than as a liquid even though there is still the same amount of matter.

Ice cubes are less dense than water which makes them float!

This property of water is important to fish and other organisms that live in lakes and ponds that freeze over during the winter.

•Question: Explain what happens to liquid water as it freezes.

Water has an unusually high specific heat. Specific heat=the amount of heat needed to

increase the temperature of a certain mass of a substance by 1 degree

Compared to other substances, water requires a lot of heat to increase its temperature. This is due to the many attractions among water molecules.

Other substances, such as air and rocks, have fewer attractions between their molecules, and their temperature increases more quickly when heated the same amount.

Effects: land areas located near large bodies of water experience less dramatic temperature changes than areas far inland.

– Q: Explain why it takes a pot of hot water a long time to heat up.

Questions

1. What causes water molecules to be attracted to one another?

2. Why does sugar dissolve well in water?

3. Describe what is happening to the water molecules as ice melts.

4. What unusual fact about ice causes it to float in liquid water?