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Properties of Water. The Universal Solvent. The Water Molecule. Simple tri-atomic molecule, H 2 O Each O-H bond is highly polar due to the high electronegativity of Oxygen Bond angle = 105° H 2 O has a bent shape, meaning the O-H bonds due not cancel = Polar Molecule. The Water Molecule.

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properties of water

Properties of Water

The Universal Solvent

the water molecule
The Water Molecule
  • Simple tri-atomic molecule, H2O
  • Each O-H bond is highly polar due to the high electronegativity of Oxygen
  • Bond angle = 105°
  • H2O has a bent shape, meaning the O-H bonds due not cancel = Polar Molecule
the water molecule1
The Water Molecule
  • δ is the Greek symbol for Delta
  • δ+ means there is a partial positive charge
  • δ – means there is a partial negative charge
  • Since there is a large difference in the electronegativity of the Oxygen and Hydrogen atoms, the element is Polar
the water molecule2
The Water Molecule
  • Water’s bent shape and ability to Hydrogen Bond give it special properties
    • High Surface Tension
    • Low Vapor Pressure
    • High Specific Heat
    • High Heat of Vaporization
    • High boiling point
  • Water molecules are attracted by Dipole Interactions
    • What are dipole interactions?
high surface tension
High Surface Tension
  • Surface Tension: the inward pull or force that tends to minimize the surface area of a liquid
  • Water forms round droplets
    • The greater the molecular force, the higher the surface tension, the more spherical the droplet
  • Water acts like it has a skin
    • Hydrogen bonding creates a large network of bonds between adjacent molecules
surface tension
Surface Tension
  • Water molecules hydrogen bond to one another due to electrostatic attraction
  • Molecules in the middle are pulled in various direction to bond with adjacent molecules
  • Molecules at the surface are pulled downward and to the side since water is not attracted to air
surface tension1
Surface Tension
  • Glass has polar molecules and has the ability to hydrogen bond
  • This attracts water molecules and causes them to be drawn up a cylinder wall
  • Plastics are non-wetting; have no attraction to water molecules
can we decrease surface tension
Can we decrease Surface Tension?
  • Use a Surfactant – Surface Active Agent
  • Also called a “wetting agent”, like detergent or soap
  • How does it work?
    • It interferes with Hydrogen Bonding
low vapor pressure
Low Vapor Pressure
  • Vapor Pressure is caused by molecules that escape the surface of a liquid and enter gaseous state
  • Hydrogen Bonding holds water molecules close so there is a low tendency to escape
  • Why is this important?
specific heat capacity
Specific Heat Capacity
  • Water has a high heat capacity (also termed specific heat)
  • It requires a large amount of energy/heat to be absorbed to change it’s temperature
  • Allows moderation of daily temperatures
    • Warm days: water absorbs heat from warmer environment decreasing air temperature
    • Cool Nights: transfer of heat from water to cooler environment increasing air temperature
evaporation and condensation
Evaporation and Condensation
  • Water absorbs large amounts of heat as it evaporates or vaporizes
  • Water gives off large amounts of heat as it condenses
  • Water = 18.02 g/mol, Liquid rather than a gas, an important exception, BP is 100°C
  • Extensive Hydrogen bonding requires more heat to disrupt bonds
slide12
Ice
  • As most liquids cool, they tend to contract (get smaller)
  • Water does not act in this manner, Why?
  • It will decrease in volume until it reaches about 4°C, then it starts to expand
    • This occurs as water molecules slow down arranging themselves in honeycomb crystal shapes
    • This expansion causes the volume of the ice to increase while the mass remains the same
    • Ice has a 10% lower density than water
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