1. Water and the Water Molecule A short lesson on water molecules designed for the Junior High science curriculum.

2. This lesson will…  Define the term molecule.  Outline the formation of a water molecule.  Introduce the characteristics that make water so unusual. Image retrieved from: http://www.accs.net/users/kriel/chapter%20seven/water%20polar.gifhttp://www.accs.net/users/kriel/chapter%20seven/water%20polar.gif

3. Before we start, let’s quickly review the definition of an atom. An atom is the smallest possible particle of a chemical element. Nucleus (+) Electron (-) Hydrogen Atom

4. The Molecule  A molecule is a group of two or more atoms held together by chemical bonds. chemical bondschemical bonds  Water is a molecule.  Ever hear someone call water, H 2 O? H O H H O H H O H

5. Chemical Bonds Definition: The energy relationship between two or more atoms that hold them together.  Chemical bonds are formed when electrons are shared between atoms or moved from one atom to another.

6. We call it H 2 O because water molecules are formed when electrons are shared between two Hydrogen atoms and one Oxygen atom. H O H H O H

7. H H O + + 105° 2- The Water Molecule  The angle formed by the 2 Hydrogen atoms and the 1 Oxygen atom is about 105°.  Water molecules have a positive (+) and negative (-) end.  This makes it attract to other water molecules.

8. Hydrogen Bonds  Hydrogen bonds form when the positive (+) end (the H atom) of one water molecule is attracted to the negative (-) end (the O atom) of another water molecule. Hydrogen Bond

9. Cohesion & Adhesion  Hydrogen bonds influence the properties of water by allowing individual water molecules to stick to each other. This is called cohesion. Cohesion gives water it’s surface tension.  Ever see an insect walk on water?  Adhesion allows water to stick to solid materials and make them wet.

10. Water  The most abundant molecule of earth.  About 70-75% of the earth’s surface is liquid and solid water.  Water molecules are also found in our atmosphere in the form of vapor.  The only pure substance found naturally in all three states of matter – liquid, solid, gas.

11. About the Author Mark Riley is a second year graduate student in the Curriculum & Instruction program at Ohio University. Please contact him by email at mr389997@ohio.edu mr389997@ohio.edu Click the button to restart this PowerPoint.

12. References Garrison, T. (2006). Essentials of Oceanography (4 th ed.)(p. 108). Belmont, CA: Thomson Brooks/Cole. http://en.wikipedia.org/wiki/Water_(molecule) http://en.wikipedia.org/wiki/Molecule