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What Makes Water Special?

Author(s): Nancy P. Moreno, PhD, Barbara Z. Tharp, MS, and Judith Dresden, MS.

The Science of Water

Most properties of water are related to the structure of the water molecule. Each water molecule consists of two hydrogen atoms and one oxygen atom. As with all molecules of this type, the oxygen atom and the hydrogen atoms share electrons. However, the electrons are not shared equally. They are pulled toward the oxygen side of the molecule, which ends up with a slight negative charge. 

Correspondingly, the hydrogen side of the molecule ends up with a slight positive charge. Each molecule in liquid water, therefore, has a positive end and a negative end. This separation of positive and negative charges (polarity) makes each water molecule act like a tiny magnet, capable of clinging to other water molecules and to any other particle or surface that is electrically charged (adhesion). The forces of attraction between the opposite charges hold the molecules together quite tightly.

The properties of water that students observed in this activity are as follows.

  • Molecules in liquid water are attracted to one another. This characteristic accounts for water’s ability to form rounded droplets and for the difficulty students’ observed in splitting water drops. Surface tension is a term describing the cohesion of water molecules at the surface of a body of water. 
  • Liquid water is an excellent solvent of many substances. This makes water particularly valuable to living organisms. All of the thousands of chemical processes inside cells take place in water. Water also carries dissolved nutrients throughout the bodies of living organisms and to transport wastes. Unfortunately, the same characteristics make liquid water easy to pollute, because so many different chemicals can be dissolved in it. 
  • Water is colorless and allows light to shine through it. Plants can grow underwater because water is transparent to the wavelengths of light needed for photosynthesis. 
  • Not all liquids behave in the same way as water. Oil, which is not made of polar molecules, does not show the same properties of mutual attraction that can be observed with water. 

 


Funded by the following grant(s)

National Institute of Environmental Health Sciences, NIH

National Institute of Environmental Health Sciences, NIH

The Environment as a Context for Opportunities in Schools
Grant Numbers: 5R25ES010698, R25ES06932


Houston Endowment Inc.

Houston Endowment Inc.

Foundations for the Future: Capitalizing on Technology to Promote Equity, Access and Quality in Elementary Science Education