Unique Properties of Water
Polar Covalent Bonds <ul><li>Polar covalent bond:  unequal sharing of electrons </li></ul>
Hydrogen Bond <ul><li>Attraction between a hydrogen atom and an atom such as oxygen or nitrogen that is either part of ano...
Unique Properties of Water <ul><li>This is the chemical basis for the unique properties of water.  </li></ul><ul><li>Life ...
Adhesion & Cohesion <ul><li>Cohesion: attraction of water for itself </li></ul><ul><li>Adhesion: attraction for water to o...
High specific heat <ul><li>Specific heat: the amount of heat required to raise or lower the temperature of 1 gram of subst...
High heat of vaporization <ul><li>Heat of vaporization: The amount of heat required for 1 gram of a substance to be conver...
Density <ul><li>Water is also unique in the way temperature affects its density.  </li></ul><ul><li>Most substances increa...
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Unique Properties Of Water

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Unique Properties of Water

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Unique Properties Of Water

  1. 1. Unique Properties of Water
  2. 2. Polar Covalent Bonds <ul><li>Polar covalent bond: unequal sharing of electrons </li></ul>
  3. 3. Hydrogen Bond <ul><li>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. </li></ul><ul><li>Both the hydrogen atom and the other atom must be involved in a polar covalent bond </li></ul>
  4. 4. Unique Properties of Water <ul><li>This is the chemical basis for the unique properties of water. </li></ul><ul><li>Life as we know it would not exist without these properties </li></ul><ul><li>Before exploring more of the unique properties of water, please take the following Water Quiz to test how much you understand already. </li></ul>
  5. 5. Adhesion & Cohesion <ul><li>Cohesion: attraction of water for itself </li></ul><ul><li>Adhesion: attraction for water to other polar or charged materials </li></ul><ul><ul><li>Surface tension: </li></ul></ul><ul><ul><ul><li>Because of the hydrogen-bonding, water acts as if it were coated with a film. This surface tension (the tough &quot;skin&quot; formed on the surface of water) causes water to &quot;bead-up&quot; on a hard, unwettable surface. Surface tension allows us to skip rocks on water and it allows small organisms like the water strider to &quot;walk on water&quot;. </li></ul></ul></ul>
  6. 6. High specific heat <ul><li>Specific heat: the amount of heat required to raise or lower the temperature of 1 gram of substance 1 degree C. </li></ul><ul><ul><li>a lot of heat energy is required to break hydrogen bonds, water resists temperature change. </li></ul></ul><ul><ul><li>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. </li></ul></ul><ul><li>Because water can absorb a lot of heat with little change in temperature, it acts as a thermal buffer. </li></ul><ul><ul><li>On a small scale, water in a cell can absorb much heat with little change in temperature. </li></ul></ul><ul><ul><li>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. </li></ul></ul>
  7. 7. High heat of vaporization <ul><li>Heat of vaporization: The amount of heat required for 1 gram of a substance to be converted from a liquid to a gas. </li></ul><ul><ul><li>Hydrogen bonds make it difficult for water molecules to escape the liquid state and are responsible for water's high heat of vaporization. </li></ul></ul><ul><ul><li>The hydrogen bonds must be broken before water can evaporate and this requires considerable energy. </li></ul></ul><ul><li>Because water has a high heat of vaporization </li></ul><ul><ul><li>Helps our bodies and our planet to maintain our temperature within a tolerable range. </li></ul></ul><ul><ul><li>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. </li></ul></ul><ul><ul><li>Water also helps moderate global climate by absorbing solar radiation and dissipating the heat by evaporation of surface water. </li></ul></ul>
  8. 8. Density <ul><li>Water is also unique in the way temperature affects its density. </li></ul><ul><li>Most substances increase in density as temperature decreases because the molecules making up the substance begin to move more slowly and get closer together. </li></ul><ul><ul><li>The density of water increases as it is cooled to 4 degrees C </li></ul></ul><ul><ul><li>and then its density begins to decrease as the temperature decreases to 0 degrees C, the freezing point of water. </li></ul></ul><ul><ul><ul><li>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. </li></ul></ul></ul><ul><ul><ul><li>This is the reason why ice floats and ponds don't freeze solid. </li></ul></ul></ul>
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