Unique Properties Of Water
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Unique Properties Of Water

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Unique Properties of Water

Unique Properties of Water

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Unique Properties Of Water Unique Properties Of Water Presentation Transcript

  • Unique Properties of Water
  • Polar Covalent Bonds
    • Polar covalent bond: unequal sharing of electrons
  • Hydrogen Bond
    • Attraction between a hydrogen atom and an atom such as oxygen or nitrogen that is either part of another molecule or located at a distant site on the same molecule.
    • Both the hydrogen atom and the other atom must be involved in a polar covalent bond
  • Unique Properties of Water
    • This is the chemical basis for the unique properties of water.
    • Life as we know it would not exist without these properties
    • Before exploring more of the unique properties of water, please take the following Water Quiz to test how much you understand already.
  • Adhesion & Cohesion
    • Cohesion: attraction of water for itself
    • Adhesion: attraction for water to other polar or charged materials
      • Surface tension:
        • Because of the hydrogen-bonding, water acts as if it were coated with a film. This surface tension (the tough "skin" formed on the surface of water) causes water to "bead-up" on a hard, unwettable surface. Surface tension allows us to skip rocks on water and it allows small organisms like the water strider to "walk on water".
  • High specific heat
    • Specific heat: the amount of heat required to raise or lower the temperature of 1 gram of substance 1 degree C.
      • a lot of heat energy is required to break hydrogen bonds, water resists temperature change.
      • When water is heated, most of the heat is used to break hydrogen bonds and not much is left over to raise the temperature of the water.
    • Because water can absorb a lot of heat with little change in temperature, it acts as a thermal buffer.
      • On a small scale, water in a cell can absorb much heat with little change in temperature.
      • On a larger scale, the water in the ocean acts as a thermal buffer for the earth, resisting temperature change and creating a hospitable environment for life.
  • High heat of vaporization
    • Heat of vaporization: The amount of heat required for 1 gram of a substance to be converted from a liquid to a gas.
      • Hydrogen bonds make it difficult for water molecules to escape the liquid state and are responsible for water's high heat of vaporization.
      • The hydrogen bonds must be broken before water can evaporate and this requires considerable energy.
    • Because water has a high heat of vaporization
      • Helps our bodies and our planet to maintain our temperature within a tolerable range.
      • When we get hot and sweat, water evaporates from our skin and cools us. Since the evaporation of water requires a considerable amount of energy, it is very effective in cooling us.
      • Water also helps moderate global climate by absorbing solar radiation and dissipating the heat by evaporation of surface water.
  • Density
    • Water is also unique in the way temperature affects its density.
    • Most substances increase in density as temperature decreases because the molecules making up the substance begin to move more slowly and get closer together.
      • The density of water increases as it is cooled to 4 degrees C
      • and then its density begins to decrease as the temperature decreases to 0 degrees C, the freezing point of water.
        • As the freezing point is approached, hydrogen bonds relax and form a crystal lattice that keeps molecules further apart than they are in liquid water.
        • This is the reason why ice floats and ponds don't freeze solid.