Life s Chemical Basis. Chapter 2

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1 Life s Chemical Basis Chapter 2

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

3 Atoms Determine the behavior of elements make up all living things Building blocks of all substances protons, neutrons, electrons Charge electrical property attracts or repels other subatomic particles

4 Subatomic Particles Electrons negative charge move around the nucleus Protons positive charge in the nucleus Neutrons no charge in the nucleus

5 Characteristics of Atoms Atoms differ in the # of subatomic particles: Atomic Number number of protons determines the element Mass Number number of protons and neutrons determines isotopes

6 + 0 Proton Neutron Electron Matter Everything is made of matter Matter is made of atoms Hydrogen 1 proton 1 electron Oxygen 8 protons 8 neutrons 8 electrons

7 The World of Elements

8 Periodic Table An arrangement of the elements based on their atomic number and chemical properties

9 Essential Elements of Life ~25 elements are essential to life 4 make up 96% of living matter Carbon Hydrogen Oxygen Nitrogen 4 make up almost the rest Phosporus Sulfur Calcium Potassium

10 Bonding Properties Electrons Determine the chemical behavior of an atom Depends on # of valence e - (outer shell) How does this atom behave?

11 Bonding Properties How does this atom behave? How does this atom behave?

12 Why Atoms Interact The shell model of electron orbitals diagrams electron vacancies; filled from inside out First shell: one orbital (2 electrons) Second shell: four orbitals (8 electrons) Third shell: four orbitals (8 electrons) Atoms with vacancies in their outer shell tend to give up, acquire, or share electrons

13 Elements & Their Valence Shells Elements in the same row have the same number of shells Moving from left to right, each element has a sequential addition of electrons (& protons)

14 Elements & Their Valence Shells Elements in the same column have the same valence & similar chemical properties

15 Atoms & Ions Ion An atom with a positive or negative charge due to loss or gain of electrons in its outer shell Examples: Na +, Cl - Electronegativity A measure of an atom s ability to pull electrons from another atom

17 Chemical Reactivity Atoms tend to either: 1. Complete a partially filled valence shell -or- 1. Empty a partially filled valence shell This tendency drives chemical reactions and creates bonds

18 From Atoms to Molecules Weak bonds: Hydrogen bonds Attraction b/w + and Van der Waals forces Attraction b/w hot spots of + and due to asymmetrical electron distribution Ionic bonds Attraction b/w anion and cation

19 Ionic Bonds A strong mutual attraction between two oppositely charges ions with a large difference in electronegativity (an electron is not transferred) Example: NaCl (table salt)

21 Covalent Bonds Strong bonds 2 atoms share 1, 2, or 3 pairs of electrons Very stable Form molecules H H H H H O O H 2 (hydrogen gas) H

22 Multiple Covalent Bonds 2 atoms can share >1 pair of electrons Double bonds 2 pairs of e - Triple bonds 3 pairs of e - VERY strong bonds More is better!

23 Nonpolar Covalent Bond Pair of electrons shared equally by 2 atoms Ex: methane (CH 4 ) balanced, stable, good building block

24 Polar Covalent Bond Pair of electrons shared unequally by 2 atoms Ex: water (H 2 O) Oxygen has a stronger attraction to the e- More electronegative Water is a polar molecule + vs poles leads to many interesting properties of water H Oxygen H

25 Hydrogen Bonds Polar water creates molecular attractions Attraction b/w one +H of one molecule and one O of another molecule Remember, it is a weak bond Stabilize the structures of large biological molecules

27 Chemical Reactions Make and break chemical bonds Reactants Starting molecules Products Final molecules Ex: 6 CO2 + 6 H20 C6H12O6 + 6 O2

28 Why Are We Studying Water? All life occurs in water Inside and outside the cell

29 Chemistry of Water H 2 O is a polar molecule Polar covalent bonds + and - poles

30 Chemistry of Water Hydrogen bonds form between 2 H 2 O molecules + attracted to Sticky molecule

31 4 Properties of Water Facilitate an environment for life: Cohesive behavior Ability to moderate temperature Expansion upon freezing Versatility as a solvent

32 Cohesion Created by H-bonding between H 2 O molecules H 2 O is sticky Surface tension

33 Adhesion H 2 O molecules form bonds with other substances Capillary action Meniscus H 2 O climbs up fiber Ex: paper towel

34 Transpiration How water gets to the top of a tree

35 Moderation of Temperature H 2 O resists changes in temp. High specific heat Takes a lot to heat it up Takes a lot to cool it down H 2 O moderates temperatures on Earth

36 Heat of Vaporization

37 Evaporative Cooling Organisms rely on heat of vaporization to remove heat

38 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 And this has made all the difference!

39 Ice Floats

40 Why is ice floats important? Oceans & lakes don t freeze solid Surface ice insulates water below Allows life to survive the winter If ice sank Ponds, lakes, & oceans would freeze solid In summer, only a few inches would thaw Seasonal turnover of lakes nutrient cycling

41 Water is the Solvent of Life Solvent The dissolving agent Solute The substance that is dissolved Solution A liquid that is a homogenous mixture of substances

42 Water is the Solvent of Life Polarity makes H 2 O a good solvent Polar H 2 O molecules surround + and ions

43 What Dissolves in Water? Hydrophilic molecules Substances have an attraction to H 2 O Polar or nonpolar?

44 What Doesn t Dissolve in H 2 O? Hydrophobic substances Don t have an affinity for H 2 O Polar or nonpolar? Oh, look hydrocarbons! fat (triglycerol)

45 Ionization of Water and ph Water ionizes H+ splits off from H 2 O, leaving OH if [H+] = [-OH], water is neutral if [H+] > [-OH], water is acidic if [H+] < [-OH], water is basic ph scale how acid or basic solution is H 2 O H + + OH

tenfold change in H+ ions ph1 ph2 10-1 10-2 10 times less H + ph8

46 tenfold change in H+ ions ph1 ph times less H + ph8 ph times more H + ph10 ph times more H +

ph Buffers & Cellular Regulation ph of cells must be kept ~7 ph affects shape of molecules shape of molecules affect function ph affects cellular function

47 ph Buffers & Cellular Regulation ph of cells must be kept ~7 ph affects shape of molecules shape of molecules affect function ph affects cellular function Control ph by buffers reservoir of H+ donate H+ when [H+] falls absorb H+ when [H+] rises Amount of base added Buffering range

Review!! 1. Many mammals control their body temperature by sweating. Which property of water is most directly responsible for the ability of sweat to lower body temperature?

48 Review!! 1. Many mammals control their body temperature by sweating. Which property of water is most directly responsible for the ability of sweat to lower body temperature? a) Water s change in density when it condenses b) Water s ability to dissolve molecules in the air c) The release of heat by the formation of hydrogen bonds d) The absorption of heat by the breaking of hydrogen bonds e) Water s high surface tension

49 2. The following are ph values: cola-2; orange juice-3; beer-4; coffee-5; human blood-7.4. Which of these liquids has the highest molar concentration of OH-? a) cola b) orange juice c) beer d) coffee e) human blood

50 3. Based on your knowledge of the polarity of water, the solute molecule is most likely. a) positively charged b) negatively charged c) neutral in charge d) hydrophobic e) nonpolar

51 4. If the ph of a solution is increased from ph 8 to ph 9, it means that the a) concentration of H+ is 10 times greater than what it was at ph 8. b) concentration of H+ is 100 times less than what it was at ph 8. c) concentration of OH- is 10 times greater than what it was at ph 8. d) concentration of OH- is 100 times less than what it was at ph 8. e) concentration of H+ is greater and the concentration of OH- is less than at ph 8.

52 Questions???

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