2.1-2 Chemistry and Water

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Amie Lindsey
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1 Prepared by Kim Foglia. Adapted and modified by Nhan Pham Chemistry and Water

2 Objectives Discuss why we study chemistry in biology Review structure of an atom Explain the role of valence electrons in chemical bonding Distinguish different types of bonds

3 Why study chemistry in a biology class?

4 Life requires ~25 chemical elements About 25 elements are essential for life 4 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)

5 The Atom indivisible unit of matter 100 million atoms side by side ~ 1 cm

7 The Octet Rule Electrons determine the chemical behavior of atom Valence electrons (on the outer most shell) 8 is the magic number!

8 Bonding properties How does this atom behave?

9 Chemical reactivity Atoms tend to: complete a partially filled valence shell OR empty a partially filled valence shell This tendency drives chemical reactions and creates bonds

10 Sodium Metal in Water

11 Bonds in Biology Weak bonds - ionic - hydrogen bonds - hydrophobic and hydrophilic interactions - van der Waals interaction Strong bonds - covalent bonds Hydrogen bond Covalent bond H 2 (hydrogen gas)

12 Bond Strength

13 Ionic Bond 1 or more electrons are transferred from one atom to another atom Ex: NaCl (table salt) Why?

14 Covalent bonds Why are covalent bonds strong? - two atoms share a pair of electrons - both atoms holding onto the electrons - very stable forms molecules H H H H H O Oxygen H 2 (hydrogen gas) H H 2 O (water)

15 Multiple covalent bonds 2 atoms can share more than 1 pair of electrons double bonds triple bonds

16 van der Waals slight attraction between oppositely charged regions of nearby molecules

17 Objectives Explain why water is polar Examine different properties of water and explain how they are good for living things

18 Station 1 Surface Tension and Adhesion Water molecules stick to each other Cohesion Such stickiness creates high surface tension

19 Water is a Polar Molecule Oxygen wants electrons a lot more than hydrogen à pulls electrons toward itself à becomes a slightly negative pole The hydrogen atoms become positive poles

20 Hydrogen Bond This is why water molecules stick to each other like little magnets

21 Station 2 Climbing Property Water molecules not only stick to each other, they also stick to other molecules (adhesion) climb up the piece of paper and inside tree trunks

22 How does H 2 O get to top of trees? Transpiration is built on cohesion and adhesion

23 Station 3 Polarity of Water Water is polar Oil is non-polar à They don t MIX How is this good for living things?

Water dissolves many substances that are polar,

24 Station 4 Universal Solvent Solvent substance that dissolve, or break apart, another substance (solute) Water dissolves many substances that are polar, ionic, and even non-polar How is this good for living things?

25 Water is the solvent of life What makes H 2 O a good solvent? POLARITY polar H 2 O molecules surround (+) and ( ) ions

26 Dissolved Oxygen in Blood

27 Station 5 High Specific heat It takes a long time for water to change temperature à high specific heat How is this good for living things?

28 Specific heat H 2 O resists changes in temperature H 2 O moderates temperatures on Earth

29 The special case of ice Most (all?) substances are more dense when they are solid but not water. Why is this property important?

31 Ionization of water & ph Water ionizes ph scale H 2 O H + + OH

ph Scale tenfold change in H+ ions ph1 ph2 10-1 10-2 10 times less H + ph8 ph7 10-8 10-7 10 times more H + ph10 ph8 10-10 10-8 100 times more H + H + Ion Concentration 10 0 10 1 ph 0 1 10 2 2

32 ph Scale tenfold change in H+ ions ph1 ph times less H + ph8 ph times more H + ph10 ph times more H + H + Ion Concentration ph Examples of Solutions Hydrochloric acid Battery acid Stomach acid, Lemon juice Vinegar, cola, beer Tomatoes 10 5 Black coffee, Rainwater Urine, Saliva Pure water, Blood Seawater 10 9 Baking soda Great Salt Lake Household ammonia Household bleach Oven cleaner Sodium hydroxide

33 Buffers and Cellular Regulation ph of cells must be kept ~7. Why? ph affects shape of molecules shape of molecules affect function à ph affects cellular function 9 Control ph by buffers reservoir of H + - donate H+ when [H + ] falls - absorb H+ when [H + ] rises ph Amount of base added Buffering range

Why are we studying chemistry?

The Chemistry of Life Why are we studying chemistry? Chemistry is the foundation of Biology 1 Everything is made of matter Matter is made of atoms Hydrogen 1 proton 1 electron Oxygen 8 protons 8 neutrons