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 ~ 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

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

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

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 - substancedissolved

• Polar or charged solutes

can “stick” to water

molecules (i.e. Dissolve)

Na+

Cl–

– –

––

––

–

––

– –

+ ++

+

+

+

+

+

+

+

+

++ +

+

+

+

+

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.

Why does ice float?

PHASES OF WATER