Surface Tension Water Bead or Dome H H O H O H H H O H H H O Penny Water Molecule H H H H O O H H O H H O H O H H H O H O H H O Water molecules are too small for us to see with our eyes alone, but they are composed of one Oxygen (O) atom and two Hydrogen (H) atoms. This is why water is commonly called H2O. Have you heard the saying opposites attract? In a way the atoms that make up a water molecule are kind of like magnets. The hydrogen atoms are positively charged and the oxygen atoms are negatively charged so the water molecules are attracted to each other. This attraction causes the molecules to want to “stick” together and form a dome on a waterproof surface. H H O -H H O Attraction + Surface Tension Soapy Water Plain Water H H H O H O H H H O H H H H O H H O O H H O H H H O H H O H O H H H O Penny H O H O H H H O H H O H O H H H OH H O H H O H H H H O O H O Penny Soap Molecule In our new model, the blue rectangle represents a soap molecule. Soap molecules act as a “barrier.” When soap is present in the water, the water molecules have a harder time attracting each other so surface tension is reduced. As a result, fewer water molecules will fit on the same penny.