Properties of Water – Physical Science Basics
More than 70% of Earth’s surface is covered by water, with about 96.5% of it in the global oceans. This amazing substance is essential for all life on our planet and helps maintain Earth’s climate. Water has several unique properties that distinguish it from most other substances.
Water has both a high boiling point (100°C; 212°F) and a low freezing point (0°C; 32°F). Consequently, it can be found naturally as a solid (ice or snow), a liquid (liquid water) and a gas (steam or water vapor), at any given time on our planet.
Liquid water changes temperature very slowly. This characteristic helps animals to maintain their body temperatures. It also keeps large areas of water from warming or cooling rapidly, thereby helping to regulate Earth’s climate.
Liquid water is an excellent solvent. This property makes water 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 transports wastes. Unfortunately, the same characteristics make liquid water easy to pollute, because so many different chemicals can be dissolved in it.
Molecules in liquid water are attracted to one another and, as a result, “stick” very closely together. This properly explains water’s ability to form rounded droplets and to rise within a thin, hollow tube. This characteristic is important for plants, which conduct water and nutrients through very narrow tubes extending from the roots to the branches and leaves.
Liquid water expands when it becomes a solid (ice). Most substances take up less space when they are transformed from a liquid to a solid. Water, on the other hand, actually takes up more space as a solid because the molecules in ice crystals are farther apart than those in liquid water. Since it is less dense, ice floats on top of liquid water.
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.
Most of these properties are related to the structure of the water molecule, which consists of two hydrogen atoms and one oxygen atom. The oxygen atom and the hydrogen atoms share electrons, but the electrons are not shared equally. The electrons 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. This separation of positive and negative charges (polarity) causes each water molecule to act like a tiny magnet, capable of clinging to other water molecules and to any other electrically charged particle or surface.
Keywords: lesson | physical science | water | water molecule | three states of water | properties of water | polarity | water cycle | hydrologic cycle | precipitation | condensation | transpiration | evaporation | ground water | ocean | lake | river | water supply | water source | ground water
- Composite image courtesy of NASA Earth Observatory.
- Moreno, N., Tharp, B., and Dresden, J. (2011) The Science of Water Teacher’s Guide. Baylor College of Medicine: Houston.
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My Health My World: National Dissemination
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The Environment as a Context for Opportunities in Schools
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Foundations for the Future: Capitalizing on Technology to Promote Equity, Access and Quality in Elementary Science Education