Properties of water
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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

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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


Properties of water

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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