Chemistry and Seawater

1. ChemistryandSeawater

2. Basic chemistry • Atomic structure • Nucleus = protons (positive) + neutrons (neutral) http://www.rstp.uwaterloo.ca/manual/matter/graphic/atom.jpg

3. Found in shells around nucleus • 1st shell can hold 2 electrons; 2nd and 3rd shells can hold 8 electrons • Not all atoms have shells that are completely filled • Atoms bond with other atoms to fill outer shell • Electrons (negative charge)

4. Chemical bonds • Attractive force that holds atoms together • Three major types • Ionic bonds • Covalent bonds • Hydrogen bonds

5. http://serc.carleton.edu/images/usingdata/nasaimages

6. Ionic bonds – weak bonds • Atoms “exchange” electrons  fill outer shell •  becomes positive ion if lose electron •  becomes negative ion if gain electron • + & – ions attracted to each other • Na & Cl  Na+ + Cl- http://www.physicalgeography.net/fundamentals/images http://www.msnucleus.org/membership/html/k-6/rc/minerals/3

7. Covalent bonds – strong bonds • Atoms “share” electrons to fill outer shell • H (hydrogen) has one electron, needs 1 more • O (oxygen) has 6 electrons in outer shell, needs two electrons • Therefore, oxygen and 2 hydrogens bond to form water • Covalent bonds are stronger because there is sharing of the electrons http://www.theochem.ruhr-uni-bochum.de/~axel.kohlmeyer/cpmd-vmd http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/chem/notes/chpt2

8. Polarity of covalent bonds • Nonpolar covalent – electrons are shared equally • Polar covalent - electrons not equally distributed in molecule • Water is a dipolar molecule (two polar covalent bonds) • O strongly attracts electrons  slightly negative • H slightly positive • Think of oxygen as being the “bully” – it’s larger so it pulls the electrons towards it’s nucleus more often • Allows formation of H-bonding between water molecules

9. H2O molecule • One hydrogen H and two oxygen O atoms bonded by sharing electrons • Both H atoms on same side of O atom • Dipolar covalent bond

10. Hydrogen bonding • Polarity  • small negative charge at O end • small positive charge at H end • Attraction between + and – ends of water molecules to each other or other ions • Happens because of the polar covalent bond Fig. 5.3

11. Hydrogen bonding and water • Hydrogen bonds are weaker than covalent bonds but still strong enough to result in unique properties of water • Cohesion = sticks to other water molecules • Adhesion = sticks to other types of molecules • High surface tension http://faculty.uca.edu/~benw/biol1400 http://ucsu.colorado.edu/~meiercl/photography

12. Hydrogen bonding and water • H-bonds absorb red light, reflect blue light blue color • High solubility of chemical compounds in water • Solid, liquid, gas at Earth’s surface • Unusual thermal properties • Unusual density http://www.pacific-promotion.com.fr/Phototek

13. Unusual thermal properties of H2O • H2O has high boiling point • H2O has high freezing point • Most H2O is in liquid form of water on Earth’s surface • VERY important for life http://www.magnet.fsu.edu/education/tutorials/magnetacademy/superconductivity101/images/superconductivity-temperature.jpg

14. Fig. 5.6

15. Unusual thermal properties of H2O • Water high heat capacity (specific heat) • Amount of heat required to raise temperature of 1 gram of any substance 1o C • Water can take in/lose lots of heat without changing temperature – must break H-bonds • On the other hand, rocks have low heat capacity • Rocks quickly change temperature as they gain/lose heat

16. Global thermostatic effects • Moderates temperature on Earth’s surface – water temp less variable and less extreme than air temperatures • Equatorial oceans (hot) don’t boil • Polar oceans (cold) don’t freeze solid

17. Global thermostatic effects • Marine effect • Oceans moderate temperature changes day/night; different seasons • Continental effect • Land areas have greater range of temperatures day/night and during different seasons • Look at the differences between coastal Florida compared to Orlando

18. Density of water • Density of water increases as temperature decreases down to 4oC • From 4oC to 0oC density of water decreases as temperature decreases • Density of ice is less than density of water http://www.grow.arizona.edu/img/water

19. Density of water Fig. 5.10

20. Density of water • Dissolved solids reduce freezing point of water • As water freezes, the crystalline structure “pushes out” much of the dissolved solids • Creates icy “slush” and surrounding waters become saltier • Putting salt on icy roads melts ice • Salt lowers freezing point of water on roads allowing it to remain liquid at colder temps http://www.ibarron.net/users/robert/pics/2003/Norway/OsloFjord11.jpg

21. Water = Life • Summary: • Unique properties of water that make life possible • High heat capacity and specific heat • Moderates climates • Keeps equatorial regions from boiling and pole regions from freezing solid • High latent heat – when undergoing change of state, large amount of heat is absorbed or released • Sweat evaporating from your skin draws heat from your body, keep you cool • Ice is less dense than liquid water • Cohesion • Water moving up xylem in plants • Surface tension – allows plankton to stay near surface of water

22. Salinity • Six elements make up 99% of dissolved solids in seawater – from erosion of land, volcanism • Total amount of solid material dissolved in water- Traditional definition • Typical salinity is 3.5% or 35o/oo • o/oo or parts per thousand (ppt) = grams of salt per kilogram of water (g/Kg ) • Adding salts changes many properties of water Fig. 5.12

23. Pure water vs. seawater

24. Salinity variations • Open ocean salinity 33 to 38 o/oo • However, coastal areas salinity varies more widely • Influx of freshwater lowers salinity or creates brackish conditions • Greater rate of evaporation raises salinity or creates hypersalineconditions • Salinity may vary with seasons (dry/rain)

25. Deep ocean variation of salinity • Surface ocean salinity is variable • Due to occurrences at surface – rain, evaporation, etc • Deeper ocean salinity is nearly the same (polar source regions for deeper ocean water) • Halocline, rapid change of salinity with depth

26. pH – Acidity and alkalinity • Acid releases H+ when dissolved in water (HCl, H2SO4) • Alkaline (or base) releases OH- (NaOH) • pH scale measures the hydrogen ion concentration • Low pH value, acid • High pH value, alkaline (basic) • pH 7 = neutral http://www3.oes.edu/ms/science6/Pictures%20of%20Science%20Concepts/pH%20Scale.gif

27. Figure 5.17

28. Oceans absorb carbon dioxide from the atmosphere • How do humans put excess CO2 in atmosphere? • CO2 reacts with seawater to form carbonic acid • Releases H+ , decreasing pH • The additional H+ bind to carbonate ions to form bicarbonate • Less carbonate in the water makes it difficult for corals, mollusks, echinoderms, calcareous algae, etc. to form calcium carbonate

29. Ocean Acidification • Ocean water is basic – pH ~8.1 • Surface waters have already absorbed enough CO2 to experience a pH decrease of 0.1 since pre-industrial times • May not seem like a lot but remember that pH is measured on a logarithmic scale so that represents a 30% drop in a relatively short time period

30. Density of seawater • 1.022 to 1.030 g/cm3 surface seawater • Saltwater more dense than pure water • That is why you can float better in saltwater • Ocean layered according to density • Density seawater controlled by temperature, salinity, and pressure • Most important influence is temperature • Density increases with decreasing temperature

31. Density of seawater • Overall, temp has greatest effect on density • However, salinity greatest influence on density in polar oceans • polar ocean is isothermal (same temperature as depth increases) • Currents from lower latitudes bring higher salinity water into polar areas • But polar waters are overall isothermal AND isopycnal http://www.waterencyclopedia.com/images/wsci_03_img0394.jpg

32. Density versus depth • Pycnocline, abrupt change of density with depth • Thermocline, abrupt change of temperature with depth • Density differences cause a layered ocean • Mixed surface water • Pycnocline and thermocline • Deep water

34. Misconceptions • Increases in global temperatures in the atmosphere and the consequent warming of the oceans will only create a problem for people living along the coast. • Water exists in the ground in actual rivers or lakes that are constantly renewed. • People drink bottle water because it is better for our health; the safety of tap water is below consumption standards.

35. Ocean Literacy Principles • 1e - Most of Earth’s water (97%) is in the ocean. Seawater has unique properties: it is saline, its freezing point is slightly lower than fresh water, its density is slightly higher, its electrical conductivity is much higher, and it is slightly basic. The salt in seawater comes from eroding land, volcanic emissions, reactions at the seafloor, and atmospheric deposition. • 1g - The ocean is connected to major lakes, watersheds and waterways because all major watersheds on Earth drain to the ocean. Rivers and streams transport nutrients, salts, sediments and pollutants from watersheds to estuaries and to the ocean. • 3a - The ocean controls weather and climate by dominating the Earth’s energy, water and carbon systems.

36. Sunshine State Standards • SC.6.E.7.1 Differentiate among radiation, conduction, and convection, the three mechanisms by which heat is transferred through Earth's system. • SC.6.E.7.6 Differentiate between weather and climate. • SC.8.P.8.1 Explore the scientific theory of atoms (also known as atomic theory) by using models to explain the motion of particles in solids, liquids, and gases. • SC.8.P.8.4 Classify and compare substances on the basis of characteristic physical properties that can be demonstrated or measured; for example, density, thermal or electrical conductivity, solubility, magnetic properties, melting and boiling points, and know that these properties are independent of the amount of the sample. • SC.8.P.8.6 Recognize that elements are grouped in the periodic table according to similarities of their properties. • SC.8.P.8.8 Identify basic examples of and compare and classify the properties of compounds, including acids, bases, and salts. • SC.912.E.7.9 Cite evidence that the ocean has had a significant influence on climate change by absorbing, storing, and moving heat, carbon, and water. • SC.912.P.8.4 Explore the scientific theory of atoms (also known as atomic theory) by describing the structure of atoms in terms of protons, neutrons and electrons, and differentiate among these particles in terms of their mass, electrical charges and locations within the atom • SC.912.P.8.5 Relate properties of atoms and their position in the periodic table to the arrangement of their electrons.