2. Why are we studying chemistry? Chemistry is the foundation of Biology

3. Life requires ~26 chemical elements About 26 elements are essential for life – Four elements make up 96% of living matter: carbon (C) hydrogen (H) oxygen (O) nitrogen (N) – Four elements make up most of remaining 4%: phosphorus (P) calcium (Ca) sulfur (S) potassium (K)

4. Atomic Structure

5. Electrons Outside the nucleus Involved in chemical bonding How many bonds an atom can form is dependent on the # valence electrons it has. – An electron in the outer shell of an atom that can be lost or shared. – Atoms usually react to have 2 electrons in the first shell, 8 in the second, and 8 in the third. ( octet rule)

6. Octet Rule

7. Carbon

8. Oxygen

9. – – H 2 (hydrogen gas) Covalent bond Bonds in Biology Weak bonds – hydrogen bonds attraction between + and – – hydrophobic & hydrophilic interactions interaction with H 2 O – van derWaals forces – (ionic) Strong bonds – covalent bonds Hydrogen bond H2OH2O H2OH2O

10. Why are we studying water? All life occurs in water – inside & outside the cell

11. Water is a Polar Covalent Compound - which means that the electrons are not shared evenly

12. Elixir of Life Ice! I could use more ice! Special properties of water 1.cohesion & adhesion surface tension, capillary action 2.good solvent many molecules dissolve in H 2 O hydrophilic vs. hydrophobic 3.lower density as a solid ice floats! 4.high specific heat water stores heat 5.high heat of vaporization heats & cools slowly

13. 2004-2005 Cohesion H bonding between H 2 O creates cohesion – water is “sticky” – surface tension – drinking straw can you suck sugar up a straw?

14. Adhesion H 2 O molecules form H bonds with other substances – capillary action – meniscus – water climbs up fiber ex. paper towel

15. 2004-2005 Water is the solvent of life H 2 O is a good solvent due to its polarity – polar H 2 O molecules surround + & – ions – solvents dissolve solutes creating aqueous solutions

16. 2004-2005 Hydrophilic – substances have affinity for H 2 O – polar or non-polar? – ionic

17. 2004-2005 Hydrophobic – substances do not have affinity for H 2 O – polar or non-polar? – non-ionic fat (triglycerol)

18. 2004-2005 The special case of ice Most (all?) substances are more dense when they are solid But not water… Ice floats! – H bonds form a crystal with loose structure

19. Ice floats

20. Why is “ice floats” important? Oceans & lakes don’t freeze solid – if ice sank… eventually all ponds, lakes & even ocean would freeze solid during summer, only upper few inches would thaw – surface ice insulates water below allowing life to survive the winter – seasonal turnover of lakes cycling nutrients

21. Specific heat H 2 O has high specific heat – due to H bonding H 2 O resists changes in temperature – takes a lot to heat it up – takes a lot to cool it down H 2 O moderates temperatures on Earth

22. 2004-2005

23. Evaporative cooling Organisms rely on heat of vaporization to remove heat

24. Water forms ions Hydrogen ion (H + ) splits off from water to leave a hydroxide ion ( - OH) H 2 0 ----> H + + - OH If concentration of 2 ions is equal, water is neutral If [H + ] > [ - OH], water is acidic If [ - OH] > [H + ], water is basic pH scale = how acidic or basic a solution is

25. pH Scale In pure water only 1 water molecule in every 554 million is dissociated. – very small amount of ions – [H + ] or [OH - ] is 10 -7 M [H + ] [OH - ] = 10 -14 pH scale is based on this equation

26. 2004-2005 pH Scale In neutral solution [H + ] = 10 -7  pH = 7 Values for pH decline as [H + ] increase Acids – adding acid increases [H +] Bases – adding base increases [OH - ]

27. pH & Biology pH of a neutral solution = 7 Acidic solutions =pH 7 Most biological fluids have pH 6 – 8 – pH values in human stomach can reach 2 Each pH unit represents a 10-fold difference in H + & OH - concentrations. – small change in pH actually indicates a substantial change in [H + ] & [OH - ]

28. Water is a polar molecule The special properties of water make life on Earth possible The chemical behavior of water governs how organisms function Punchline