Unique Properties of Water

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Unique Properties of Water
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Polar Covalent Bonds

• Polar covalent bond unequal sharing of electrons

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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

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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.

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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 surface.
  Surface tension allows us to skip rocks on water
  and it allows small organisms like the water
  strider to "walk on water".

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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.

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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.

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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.