1. Seawater- Physics & Chemistry Marine Science 2010

2. Water The most common substance on the Earth’s surface! 98% is seawater Seawater is a mixture of: –96.5% water –3.5% salt –Minute amounts of other substances

3. Origin of Ocean & Atmosphere Volcanic activity is the sources of water in the ocean & gases in the atmosphere. Atmosphere: –Oxygen (21%) –Nitrogen (78%) –Other (Argon, Carbon dioxide, Methane, & Inert gases)

4. Structure of an Atom Atom: –Proton (+) –Neutron (no charge) –Electron (-)

5. Molecular Structure of Water Attractive forces between atoms hold molecules together. –Covalent bonds: each atom retains its electrons but shares them with adjacent atoms. –Ionic bonds: strong bonds between molecules or atoms that have lost or gained electrons. –Hydrogen bonds: determines the physical and chemical properties of water.

6. Hydrogen Bonds Result from the small size of hydrogen atoms compared to the large oxygen atoms. –Each oxygen atom has 3 electron pairs in its electron cloud. –Sharing 1 pair with 2 hydrogen atoms forming covalent bonds.

7. Asymmetrical Structure The oxygen side of the molecule is negative because of the two unshared electron pairs. The 2 hydrogen atoms on the other side make it positive. The net charge is zero (negative & positive charges are equal)! Oxygen

8. Asymmetrical Structure However, the molecular structure causes it to behave as if it had a positive and negative side (polar molecule). Two hydrogen atom form weak hydrogen bonds with oxygen of adjacent water molecules. Oxygen

9. States of Matter 3 states of matter: –Gas, solid, liquid. Each state has specific properties based on its molecular structure! Water occurs in all 3 states on Earth.

10. GAS Gas: –Molecules move independently. –Gases fill any container, no shape or size. –Striking the sides of a container exerts pressure. Adding or removing gas changes rate at which molecules strike the side. An increase or decrease temperature makes molecules faster or slower. Both change pressure!

11. Solids Opposite of gases, definite size & shape. –Bend or break with applied force. –Fixed internal structures (atoms cannot move their positions). –Vibrations increase as temperatures rise.

12. Liquids Intermediate between solids and gases. Definite volumes (size) but conform to the shape of any container in which they are placed. Atoms & molecules are loosely bonded. Bonds are easily broken, allowing them to flow.

13. Structures of Ice and Water Water molecules in ice are held together by hydrogen bonds. –Oxygen atoms form six-sided rings arranged in layers. –Each layer is a mirror image of the adjacent one. Results in an open network of atoms! Giving ice a lower density (0.92 g/cm 3 ) than water (1.0 g/cm 3 )!

14. Density Controls whether it sinks or floats in a liquid. Density is the ratio of mass to unit volume. A mass sinks through fluids less dense than itself. Eventually it reaches a point where the fluid below is denser and the fluid above is less dense. –A fluid parcel may spread out at this point forming a layer.

15. Impacts of Temperature, salinity, and pressure. Increased salinity or pressure causes density to increase. Increasing water temperature causes its density to decrease. –Warmer water = increase vibrations of atoms. –Occupies more volume = reduced density For a constant mass, density decreases as volume increases.

16. Temperature Effects on Water Temp. changes alter water’s internal structures. –Absorbed heat goes into breaking hydrogen bond. –Results in water temp. rising less than other substances after absorbing a given amount of heat. WATER HAS A HIGH HEAT CAPACITY!

17. Calories How do we measure heat? Calories –The amount of heat required to raise the temperature of 1 gram of liquid by 1 degree Celsius (°C). To break bonds in ice and water requires energy. Bonds release energy when they reform. Lets look at a graph of temperature changes when heat is added (cal per gram).

18. How is heat taken up? Sensible heat: heat we detect through touch or with thermometers. –Temp. change results from increased vibrations of molecules. Latent heat: energy required to break bonds. –Melting point & boiling point = no change in temperature. –Added energy went into breaking bonds.