The water molecule, as a whole, has 10 protons and 10 electrons, so it is neutral.In a water molecule, the oxygen atom and hydrogen atoms share electrons in covalent bonds, but the sharing is not equal.In the covalent bond between oxygen and hydrogen, the oxygen atom attracts electrons a bit more strongly than the hydrogen atoms.The unequal sharing of electrons gives the water molecule a slight negative charge near its oxygen atom and a slight positive charge near its hydrogen atoms.When a neutral molecule has a positive area at one end and a negative area at the other, it is a polar molecule.Water molecules attract one another based on the attraction between the positive end of one water molecule and the negative end of another.
Students will be introduced to the idea that water has a slight positive charge at one end of the molecule and a slight negative charge at the other (a polar molecule). Students view animations, make illustrations, and use their own water molecule models to develop an understanding of how the polar nature of water molecules can help explain some important characteristics of water.
Students will be able to explain, on the molecular level, what makes water a polar molecule. Students will also be able to show in a drawing that the polar nature of water can explain some of water’s interesting characteristics and help explain its evaporation rate compared to a less polar liquid.
The activity sheet will serve as the “Evaluate” component of each 5-E lesson plan. The activity sheets are formative assessments of student progress and understanding.
Be sure you and the students wear properly fitting goggles. Isopropyl alcohol is flammable. Keep it away from flames or spark sources. Read and follow all warnings on the label. Use in well-ventilated room. Dispose of small amounts down the drain or according to local regulations.
Materials for Each GroupStyrofoam water molecule models from Chapter 2, Lesson 2 (two per student)Permanent markers (blue and red)Isopropyl alcohol (70% or higher)WaterBrown paper towelDroppers
Note about the Materials
Students made molecular models of the water molecule using Styrofoam balls and toothpicks in Chapter 2, Lesson 2. Give each student two of these water molecule models for this activity.