Water Review

Water is the solvent of life

Unique properties of water
Polar Molecule
Cohesive
Stabilizes Temperature
Solvent of Life

Like no other common substance, water exists in nature in all three physical states:
as a solid
as a liquid
as a gas

What allows this drop of water to hang there without falling?

Polar covalent ~ water In 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

The slight differences in charge bond water molecules together (H-Bonding)

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

Cohesion: Water molecules stick together surface tension

Surface Tension

Cohesion: water molecules can move great distances

Temperature Water’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

Hydrogen Bonding in Water

Water is the universal solvent
Solution - a homogenous mixture of two or more substances : aqueous solutions
Solvent - dissolving agent (water)
Solute - substance dissolved
Polar or charged solutes
can “stick” to water
molecules
(i.e. Dissolve)

Na + Cl – – – – – – – – – – – – + + + + + + + + + + + + + + + + + +

Water
Pola r~ 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.

Why does ice float?

PHASES OF WATER

Water Review

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Water Review

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