1 Chapter 2 and 3 The Chemical Context of Life and Properties of Water

2 Essential Elements Essential elements in living things include carbon C, hydrogen H, oxygen O, and nitrogen N making up 96% of an organism A few other elements Make up the remaining 4% of living matter

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4 Deficiencies (a) Nitrogen deficiency (b) Iodine deficiency (Goiter) If there is a deficiency of an essential element, disease results

5 Trace Elements Trace elements Are required by an organism in only minute quantities Minerals such as Fe and Zn are trace elements

6 Basics You Should Know Matter Elements Compounds Atoms Subatomic Particles Atomic Number Atomic Mass Isotopes Electron Shells/Energy Levels Electron Orbitals

7 Periodic table –Shows the electron distribution for all the elements Second shell Helium 2 He First shell Third shell Hydrogen 1 H 2 He 4.00 Atomic mass Atomic number Element symbol Electron-shell diagram Lithium 3 Li Beryllium 4 Be Boron 3 B Carbon 6 C Nitrogen 7 N Oxygen 8 O Fluorine 9 F Neon 10 Ne Sodium 11 Na Magnesium 12 Mg Aluminum 13 Al Silicon 14 Si Phosphorus 15 P Sulfur 16 S Chlorine 17 Cl Argon 18 Ar Figure 2.8

8 Why do some elements react? Valence electrons –Are those in the outermost, or valence shell –Determine the chemical behavior of an atom

9 Covalent Bonding A molecule –Consists of two or more atoms held together by covalent bonds (sharing electrons) A single bond –Is the sharing of one pair of valence electrons A double bond –Is the sharing of two pairs of valence electrons

10 Cl Each chlorine atom wants to gain one electron to achieve get 8 Chlorine forms a covalent bond with itself

11 Cl

12 Cl

13 Cl

14 Cl

15 Cl 8

16 Cl circle the electrons for each atom that completes their octets 8

17 Cl circle the electrons for each atom that completes their octets Each atom has 8 electrons because they share the electrons in the middle

18 Cl circle the electrons for each atom that completes their octets It is called a SINGLE BOND

19 Cl circle the electrons for each atom that completes their octets Single bonds are shown with a dash

20 O2O2 Oxygen

21 How will two oxygen atoms bond? OO

22 OO Each atom has two unpaired electrons

23 OO

24 OO

25 OO

26 OO

27 OO

28 OO

29 Both oxygen atoms want to gain two electrons. OO

30 OO

31 OO

32 OO

33 OO

34 O O Both electron pairs are shared.

35 8 O O

36 8 O O

37 two sets of shared electrons, O O making a double bond

38 O O = The double bond is shown as two dashes. O O

39 Covalent Bonding Electronegativity –Is the attraction of a particular kind of atom for the electrons in a covalent bond The more electronegative an atom –The more strongly it pulls shared electrons toward itself

40 Covalent Bonding In a nonpolar covalent bond –The atoms have similar electronegativities –Share the electron equally

41 Figure 2.12 This results in a partial negative charge on the oxygen and a partial positive charge on the hydrogens. H2OH2O –– O H H ++ ++ Because oxygen (O) is more electronegative than hydrogen (H), shared electrons are pulled more toward oxygen. In a polar covalent bond –The atoms have differing electronegativities –Share the electrons unequally Covalent Bonding

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43 Ionic Bonds In some cases, atoms strip electrons away from their bonding partners Electron transfer between two atoms creates ions

44 FK

45 FK

46 FK

47 FK

48 FK

49 FK + _

50 FK + _ The ionic bond is the attraction between the positive K + ion and the negative F - ion

51 Ions An anion –Is negatively charged ions A cation –Is positively charged

52 Ionic Substances Na + Cl – Figure 2.14 Ionic compounds –Are often called salts, which may form crystals

53 Weak Chemical Bonds Several types of weak chemical bonds are important in living systems Van der Waals interactions –Intermolecular forces Weak chemical bonds –Reinforce the shapes of large molecules –Help molecules adhere to each other

54 Molecular Shape and Function Structure determines Function! The precise shape of a molecule –Is usually very important to its function in the living cell –Is determined by the positions of its atoms’ valence orbitals

55 Shape and Function Molecular shape –Determines how biological molecules recognize and respond to one another with specificity

56 Morphine Carbon Hydrogen Nitrogen Sulfur Oxygen Natural endorphin (a) Structures of endorphin and morphine. The boxed portion of the endorphin molecule (left) binds to receptor molecules on target cells in the brain. The boxed portion of the morphine molecule is a close match. (b) Binding to endorphin receptors. Endorphin receptors on the surface of a brain cell recognize and can bind to both endorphin and morphine. Natural endorphin Endorphin receptors Morphine Brain cell Figure 2.17

57 Chemical Reactions Chemical reactions make and break chemical bonds Chemical reactions absorb or release ENERGY (chemical energy stored in bonds)

58 Chemical Reactions Photosynthesis –Is an example of a chemical reaction Figure 2.18

59 Chemical Reactions Chemical equilibrium –Is reached when the forward and reverse reaction rates are equal

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61 Importance of water Water is the Molecule That Supports All of Life Water is the biological medium here on Earth All living organisms require water more than any other substance

62 Water Facts Three-quarters of the Earth’s surface is submerged in water The abundance of water is the main reason the Earth is habitable Figure 3.1

63 Water and Life Most animals and plants contain more than 60% water by volume. Without water life would probably never have developed on our planet.

64 Water is Polar The oxygen end (pole) of water has a negative charge The hydrogen end (pole) has a positive charge

65 Hydrogen bonding The hydrogens of one water molecule are attracted to the oxygen from other water molecules. This attractive force is called hydrogen bonding

66 Properties of water Six emergent properties of water contribute to Earth’s fitness for life 1. Cohesion/Adhesion 2. Surface tension 3. Temperature Moderation 4. High specific heat 5. Evaporative cooling 6. Universal solvent

67 Cohesion and Adhesion Hydrogen bonds give water its cohesive and adhesive properties. Cohesion-water is attracted to other water Adhesion-water attracted to other materials

68 Capillary Action Cohesion Helps pull water up through the microscopic vessels of plants Water conducting cells 100 µ m Figure 3.3

69 Surface Tension Surface tension Is a measure of how hard it is to break the surface of a liquid Is related to cohesion Figure 3.4

70 Moderation of Temperature Water moderates air temperature by absorbing heat from air that is warmer and releasing the stored heat to air that is cooler

71 Water’s High Specific Heat The specific heat of a substance is the amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1ºC 1 cal/g o C J/g o C

72 Evaporative Cooling Is due to water’s high heat of vaporization Allows water to cool a surface Sweating cools the body as heat energy from the body changes sweat into a gas

73 Insulation of Bodies of Water by Floating Ice Solid water, or ice Is less dense than liquid water and floats in liquid water Insulates water & organisms below ice layer

74 Insulation of Bodies of Water by Floating Ice The hydrogen bonds in ice Are more “ordered” than in liquid water, making ice less dense (crystal lattice) Liquid water Hydrogen bonds constantly break and re-form Ice Hydrogen bonds are stable Hydrogen bond Figure 3.5

75 The Solvent of Life Water is a versatile solvent due to its polarity It can form aqueous solutions Called the universal solvent because so many substances dissolve in water

76 Hydrophilic and Hydrophobic Substances A hydrophobic substance d oes not have an affinity for water Nonpolar lipids A hydrophilic substance h as an affinity for water Polar or ionic Carbohydrates, salts

77 Water can dissociate Into hydronium ions (H+ or H 3 O+) and hydroxide (OH-) ions Changes in the concentration of these ions Can have a great affect on pH in living organisms H Hydronium ion (H 3 O + ) H Hydroxide ion (OH – ) H H H H H H + – + Figure on p. 53 of water dissociating Effects of Changes in pH

78 Acids and Bases An acid Is any substance that increases the hydrogen ion concentration of a solution A base Is any substance that reduces the hydrogen ion concentration of a solution (more OH- ions)

79 Buffers The internal pH of most living cells Must remain close to pH 7 Buffers Are substances that minimize changes in the concentrations of hydrogen and hydroxide ions in a solution