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

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:

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

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

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.

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

H H O ° 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.

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

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.

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.

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

References Garrison, T. (2006). Essentials of Oceanography (4 th ed.)(p. 108). Belmont, CA: Thomson Brooks/Cole.