Earth- the Water PlanetAbout 71% of the Earth’s surface is covered

in waterWithout water, life cannot exist Water has unique properties that enables the

Earth to sustain life

Polar MoleculeChemical symbol : H2OCovalent bond: 2 atoms sharing electronsOxygen holds on to electrons slightly more

than the Hydrogen atoms creating a polar molecule

Water – A Polar MoleculePolarity of water molecule allows it to bond

with adjacent water moleculesBond between molecules is called a

hydrogen bondHydrogen bonds are what give water some of

it’s unique properties

Effects of Hydrogen Bonds1. High Specific Heat Capacity

Freezing point of water o° c Boiling point of water 100° c Hydrogen bonds hard to break so more

energy is required to be absorbed/released in order to change phase

Without this most or all water would be frozen in ice sheets or boiled away by the sun

Effects of Hydrogen Bonds2. Cohesion/Adhesion

H bonds attract water molecule to each other Cohesion: ability of water molecules to stick

together Cohesion gives water a more uniform

structure than most liquids Adhesion: ability of water to stick to other

materials due to its polar nature

Effects of Hydrogen Bonds3. Viscosity: tendency of a fluid to resist flow

Most fluids change viscosity as they change temperature

As water cools the viscosity rises more than in other liquids

Ex) A 20 c drop in temperature increases viscosity of water by 60%

Imp. because it affects the energy aquatic organisms must expend

Effects of Hydrogen Bonds4. Surface Tension: water’s resistance to

objects attempting to penetrate its surface Cohesive nature of water at its surface makes

this possible Many small aquatic organisms rely on surface

tension to rest (not float) on surface of the water

Affects how quickly oceans take up atmospheric CO2 and release O2 into the atmosphere

Effects of Hydrogen Bonds5. Ice Floats

Most substances become dense and sink as they cool

H bonds spread the molecules into a crystal structure that takes up more space than liquid water

With more volume, ice is less dense than water so it floats

By floating, ice forms a layer that insulates water below keeping water in liquid form

Fluid Properties: Fluid Properties: DensityDensityDensityDensity = specific = specific

weight/volumeweight/volumeD = m/v (g/cmD = m/v (g/cm33))

Density of water does Density of water does not change much.not change much.

Very high levels of Very high levels of pressure are required to pressure are required to change the density of change the density of water.water.

Density and TemperatureDensity and Temperature

????

SpecificSpecific GravityGravity ( (SGSG))

comparison of the specific weight of Hcomparison of the specific weight of H22O to O to the same volume of water under different the same volume of water under different conditions (e.g., temperature).conditions (e.g., temperature).

Often used to determine salinity via a Often used to determine salinity via a hydrometer.hydrometer.

SGSG for water is usually 1.0 and, since it is for water is usually 1.0 and, since it is dimensionless, has no units.dimensionless, has no units.

Properties of Properties of PurePure Water Water

Latent heat of fusionLatent heat of fusion: : water requires a large water requires a large loss of energy to pass loss of energy to pass from liquid to solid from liquid to solid phase. phase.

Reverse is true for Reverse is true for latent heat of latent heat of vaporization.vaporization.

Meaning: large bodies of Meaning: large bodies of water resist changes in water resist changes in temperature, life temperature, life processes remain processes remain constant.constant.

From Sumich, page 19

Physical Variables: Physical Variables: DensityDensityAlready mentioned as an aspect of fluids.Already mentioned as an aspect of fluids.Pure water is most dense at 4Pure water is most dense at 4ooC. (1 g/cmC. (1 g/cm33))Below this it becomes less dense and Below this it becomes less dense and

freezes at 0freezes at 0ooC.C.Our purposes Density of freshwater 1 g/cmOur purposes Density of freshwater 1 g/cm33

Physical Variables: Physical Variables: DensityDensityWhen you add impurities to water (e.g., When you add impurities to water (e.g.,

salt), its density increases.salt), its density increases.Density of saltwater (oceans) is 1.028 g/cmDensity of saltwater (oceans) is 1.028 g/cm33..Thus, seawater freezes at a lower temp (-Thus, seawater freezes at a lower temp (-

1.41.4ooC).C).If seawater can freeze, why doesn’t it If seawater can freeze, why doesn’t it

accumulate at the bottom of the ocean?accumulate at the bottom of the ocean?