Physical and Chemical Properties of Water

The Water Molecule Water is a compound Compound: substance that contains two or more different elements. H 2 O: 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 Capacity Temperature Density Salinity Ability to transmit light Ability to transmit sound

Heat Capacity Heat: 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 have the same density at different combinations of temperature and salinity. 10 C 12 PPT g/cm 3 21 C 15 PPT g/cm 3

Density Summary Density of Seawater is g/cm 3 Fresh is only g/cm 3 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 wavelengths are absorbed at shallow depths. -Blue light penetrates to the deepest levels and is reflected back -To our eyes. this is why the oceans appear blue.

Photic Zone Photic Zone: The depth light penetrates in the ocean. 200 meters in clear, tropical waters 100 meters in most ocean waters All photosynthetic organisms live in this zone (corals, sea grasses, algae, phytoplankton). Infrared radiation is converted to heat Most of life in the ocean is found here.

Aphotic Zone Aphotic Zone: Zone below photic zone that is in complete darkness. About 1% of light penetrates to a depth of meters Absolutely no light penetrates below 1,000 meters. ¾ or 75% of the ocean is in total darkness!

Refraction Refraction: Bending of waves. Light acts as a wave and a particle. Light bends toward The normal When it travels From a lower Density to higher Density. Light bends away from The normal when it Travels from higher density To lower density.

Snell’s Law N air =1 N water =0.75

Sound in the Ocean Sound: 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 seawater Sound 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 Layer The minimum velocity layer 1200 m depth in North Atlantic down to 600 m depth in North Pacific Sound 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 causes a shadow zone.

SONAR SONAR: Sound Navigation and Ranging.