Physical and Chemical Properties

of Water

The Water Molecule Water is a compound

Compound: substance that contains two or more different elements.

H2O: 2 hydrogens and 1 oxygen

A water molecule is held together by a Covalent Bond. Molecules are held together by

shared electrons. 2 or more water molecules are held

together by Hydrogen bonds Hydrogen Bond-When a hydrogen

atom is linked to another atom by electrostatic forces. Much stronger than covalent bonds.

Gives water properties such as cohesion and adhesion.

A Polar Molecule Molecule behaves like a

magnet. Its positive end attracts

negatively charged particles Its negative end attracts

positively charged particles Most salts are held together

by opposite charges (Na+, Cl- is NaCl) and when these come in contact with water, they are pulled apart. This is why water is a good

Solvent (dissolve things well).

Properties of Hydrogen Bonding

Cohesion-Allows individual water molecules to stick to each other (cluster), giving water a high surface tension. It also allows for diffusion. (think of the water on the penny or paper clip on water…this is due to cohesion and surface tension).

Adhesion-The tendancy of water to stick to other materials (making them wet). (capillary action in soil or water running up a paper towel).

Physical Properties of Ocean Water

Heat CapacityTemperatureDensitySalinityAbility to transmit lightAbility to transmit sound

Heat CapacityHeat: A measure of energy produced by vibration of

atoms or molecules.Temperature: A measure of how rapidly molecules

are vibrating. Heat Capacity: The amount of heat it takes to raise

1 gram of a substance by 1 degree Celsius. Water has highest heat capacity of any substance.

From hydrogen bonding!Means water’s temperature does not rise or lower very

easily.

Measuring Heat Calories per gram Heat=Specific Heat x

Change in Temperature How would we calculate

Specific Heat?

Temperature and Density Water becomes more

dense as it gets colder. UNTIL: It reaches 4

degrees Celsius. Then water becomes less

dense as it freezes Why does this happen?

Hint: Density=Mass/Volume

Salinity and Density Note that a higher

salinity gives water a higher density.

Note also that salinity decreases the temperature at which water freezes So ocean water freezes

at about -2 degrees Celsius

Fresh water freezes at 0 degrees Celsius

Temperature, Salinity, Density

Note that two samples of water can havethe same density at different combinations oftemperature and salinity.

10 C12 PPT1.010 g/cm3

21 C15 PPT1.010 g/cm3

Density SummaryDensity of Seawater is 1.020-1.030 g/cm3 Fresh is only 1.000 g/cm3

Cold, salty water is more dense than warm, less salty water.

Seawater’s density increases with increasing salinity, increasing pressure, and decreasing temperature (until right before it freezes).

Two samples of water can have the same density at different combinations of temperature and salinity.

Light in the Ocean-Long wavelengthsare absorbed at shallow depths.

-Blue light penetrates to the deepest levels and isreflected back

-To our eyes.this is why theoceans appearblue.

Photic ZonePhotic Zone: The depth light penetrates in the

ocean.200 meters in clear, tropical waters100 meters in most ocean watersAll photosynthetic organisms live in this zone

(corals, sea grasses, algae, phytoplankton). Infrared radiation is converted to heatMost of life in the ocean is found here.

Aphotic ZoneAphotic Zone: Zone below photic zone that is in

complete darkness.About 1% of light penetrates to a depth of 100-125

metersAbsolutely no light penetrates below 1,000 meters.¾ or 75% of the ocean is in total darkness!

RefractionRefraction: Bending of waves. Light acts as a

wave and a particle.

Light bends towardThe normalWhen it travelsFrom a lowerDensity to higher Density.

Light bends away fromThe normal when it Travels from higher density To lower density.

Snell’s Law

Nair=1Nwater=0.75

Sound in the OceanSound: Form of energy transmitted through a

medium through vibration of molecules. Sound intensity decreases through seawater due

to spreading, scattering, and absorption.Sound travels about 1,500 m/s in seawaterSound travels 334 m/s in air at 20 degrees C.

Speed of sound increases as temperature, pressure, and salinity increase.

Low frequencies travel farther than high frequency

Sofar LayerThe minimum velocity layer1200 m depth in North Atlantic down to 600 m

depth in North PacificSound waves move at minimum speed and allow

for sounds to heard for great distances since refraction keeps sounds waves within the layer.

Shadow Zones

80 M

Maximum sound velocity occurs at 80 m which deflects sound and causesa shadow zone.

SONARSONAR: Sound Navigation and Ranging.