Post on 18-Jul-2015
Like no other common substance, water exists in nature in all three physical states:
– as a solid– as a liquid– as a gas
Polar covalent ~ waterIn a water molecule, the oxygen is more electronegative than hydrogen
partial negative
partial positive
Oxygen pulls the shared electrons toward itself;the electrons spend more time near the oxygen atom.
Water molecules form hydrogen bonds
• Hydrogen atoms in one polar covalent molecule are attracted to an electronegative atom in another polar molecule
• This creates H-bonds
• Very important for function in biological molecules
Water’s polarity leads to hydrogen bonding and other unusual properties
• Hydrogen bonds are weak; forming and breaking constantly - but strong in high numbers
• If you could stop water in an instant most molecules would be H-bonded to another
• These characteristics (polarity & H-bonding) give water the properties of cohesion, temperature stability, and make it a universal solvent
TemperatureWater’s hydrogen bonds moderate temperature
– Water can absorb a great deal of heat energy without a large increase in temperature because It takes a lot of energy to disrupt hydrogen bonds
Heat = amount of energy associated with molecular movement
Temperature = measure of the intensity of heat: measures a substance’s molecular motion
– Add more heat to water, it disrupts H-bonds rather than increasing molecular motion
– This causes separation of water molecules and evaporation
– A water molecule takes a large amount of energy with it when it evaporates: evaporative cooling
Ice floats!Water molecules in ice (solid water) are farther
apart than the molecules in liquid water
Ice is therefore less dense than liquid water, causing it to float..
Why is this a good thing?
– If ice sank, it wouldn’t thaw
– Creates a blanket of insulation
Water is the universal solvent
• Solution - a homogenous mixture of two or more substances : aqueous solutions
• Solvent - dissolving agent (water)
• Solute - substancedissolved
• Polar or charged solutes
can “stick” to water
molecules (i.e. Dissolve)
Water• Polar~ opposite ends, opposite charges• Cohesion~ H+ bonds holding molecules together• Adhesion~ H+ bonds holding molecules to another
substance• Surface tension~ measurement of the difficulty to
break or stretch the surface of a liquid• Specific heat~ amount of heat absorbed or lost to
change temperature by 1oC• Heat of vaporization~ quantity of heat required to
convert 1g from liquid to gas states• Density……….
Chemistry of WATER
1. High heat capacity: Water heats up & cools down slower than most liquids. Holds heat longer than most. This buffers the amount of evaporating and freezing that go on in the environment.
2. High heat of vaporization: Evaporation requires a lot of energy. Sweating helps to reduce body heat. Body heat is used as energy to evaporate water. Critter loses body heat, water gains it and evaporates.
3. Solvent properties: Molecules dissolve in water, which allows them to move around more and interact. Water facilitates all chemical reactions in the body.
Chemistry of WATER
4. Cohesive & adhesive nature: Water molecules move freely, but stick together (hydrogen bonds). Great for transporting nutrients in plants, and circulation in animals.
5. High surface tension: This is another effect of hydrogen bonds. Water is tough!
6. Solid is less dense than liquid: Ice floats! Bodies of water freeze from the top down.