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This activity has been updated since it first appeared in Water Precious Water. This is the updated version.
Topic Structure of the water molecule Key Question How are electrons in the water molecule arranged? Learning Goal The students will construct a model of a water molecule. Guiding Document Project 2061 Benchmarks All matter is made up of atoms, which are far too small to see directly through a microscope. The atoms of any element are alike but are different from atoms of other elements. Atoms may stick together in well-defined molecules or may be packed together in large arrays. Different arrangements of atoms into groups compose all substances. Models are often used to think about processes that happen too slowly, too quickly, or on too small a scale to observe directly, or that are too vast to be changed deliberately, or that are potentially dangerous. Science Physical science water molecules atoms electrons Background Information See The Water Molecule fact sheets. Management 1. You may want to copy the water molecule pattern sheet onto colored paper and/or give students colored pencils to make their models more colorful. Procedure 1. Ask students if they know what water is made of. 2. Hand out the water fact sheets and discuss them with the students. 3. Hand out one water molecule pattern sheet per student. Review the various parts of the water molecule and construct the model in front of the class, defining the various parts. Refer to the illustration at the bottom of the fact sheet for the correct placement of the electrons. 4. Students can cut out and glue the electrons onto the paper atom. Connecting Learning 1. How many electrons does a hydrogen atom have? [one] 2. How many electrons does an oxygen atom have? [eight] 3. How many electrons does a water molecule have? [ten] 4. What is the difference between an atom and a molecule? [Molecules are combinations of atoms.] Integrated Processes Collecting and recording data Materials For each student: molecule pattern sheet water fact sheets glue crayons or colored pencils, optional 1 2007 AIMS Education Foundation
Key Question How are electrons in the water molecule arranged? Learning Goal construct a model of a water molecule. 2 2007 AIMS Education Foundation
3 2007 AIMS Education Foundation
All matter is made up of tiny particles called atoms. Atoms are made of even smaller particles called electrons, protons, and neutrons. The protons and neutrons are found in the center of the atom called the nucleus. The protons have a positive ( + ) charge and the neutrons have no charge. The electrons are negatively charged ( ) and spin around the nucleus of the atoms. A molecule is a combination of atoms that are bound together. A water molecule combines two hydrogen atoms with one oxygen atom which are held together by sharing electrons. H 2 + 0 = H 2 0 The hydrogen atom has one electron spinning around its nucleus. Since the energy level closest to the nucleus can hold up to two electrons, hydrogen has room for one more electron. The oxygen atom has eight electrons, two in the energy level closest to the nucleus and six more in its outer energy level. Since the outer level can hold up to eight electrons, oxygen has room for two more electrons. 4 2007 AIMS Education Foundation
Each of the two hydrogen atoms share one electron with the six electrons from oxygen completing its outer energy level. At the same time, the oxygen atom share one electron with each of the hydrogen atoms completing their outer energy levels. When the water molecule is formed, the electrons from the hydrogen atoms move closer to the oxygen atom making the electron placement unbalanced in the molecule. The hydrogen ends of the molecule then become positively charged ( + ) and the oxygen end of the molecule negatively charged ( _ ). When the ends of a molecule are positively and negatively charged, it is said to be a polar molecule. This polar characteristic causes the strong attractive force between water molecules. 5 2007 AIMS Education Foundation
Connecting Learning 1. How many electrons does a hydrogen atom have? 2. How many electrons does an oxygen atom have? 3. How many electrons does a water molecule have? 4. What is the difference between an atom and a molecule? 6 2007 AIMS Education Foundation