1. Chapter 2 The Chemical Context of Life

2. Fig. 2-3a Sodium The emergent properties of a compound

3. Fig. 2-3b Chlorine The emergent properties of a compound

4. Fig. 2-3c Sodium chloride The emergent properties of a compound

5. Essential Elements of Life Carbon, hydrogen, oxygen, and nitrogen make up 96% of living matter Most of the remaining 4% consists of calcium, phosphorus, potassium, and sulfur – Trace elements are those required by an organism in minute quantities Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

6. Table 2-1

7. Concept 2.2: An element’s properties depend on the structure of its atoms Each element consists of unique atoms – the smallest unit of matter that still retains the properties of an element Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

8. Subatomic Particles Atoms are composed of subatomic particles – Neutrons (no electrical charge) – Protons (positive charge) – Electrons (negative charge) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

9. Neutrons and protons form the atomic nucleus Electrons form a cloud around the nucleus Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

10. Cloud of negative charge (2 electrons) Fig. 2-5 Nucleus Electrons (b) (a) Simplified models of a helium (He) atom

11. Atomic Number and Atomic Mass atomic number – number of protons in the nucleus mass number – sum of protons plus neutrons in the nucleus Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

12. Isotopes – two atoms of the same element that differ in number of neutrons Radioactive isotopes – decay spontaneously, giving off particles and energy Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

13. Applications of radioactive isotopes: – Dating fossils – Tracing atoms through metabolic processes – Diagnosing medical disorders Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

14. Fig. 2-6a Compounds including radioactive tracer (bright blue) Human cells Incubators 1 2 3 4 5 6 7 8 9 50ºC 45ºC40ºC 25ºC 30ºC 35ºC 15ºC 20ºC 10ºC Human cells are incubated with compounds used to make DNA. One compound is labeled with 3 H. 1 2 The cells are placed in test tubes; their DNA is isolated; and unused labeled compounds are removed. DNA (old and new) TECHNIQUE

15. Fig. 2-6b TECHNIQUE The test tubes are placed in a scintillation counter. 3

16. Fig. 2-6c RESULTS Counts per minute (  1,000) 0 10 2030 40 50 10 20 30 Temperature (ºC) Optimum temperature for DNA synthesis

17. Fig. 2-7 Cancerous throat tissue

18. The Energy Levels of Electrons Energy is the capacity to cause change Potential energy the energy that matter has stored because of its location or structure The electrons of an atom differ in their amounts of potential energy An electron’s state of potential energy is called its energy level, or electron shell Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

19. Fig. 2-8 (a) A ball bouncing down a flight of stairs provides an analogy for energy levels of electrons Third shell (highest energy level) Second shell (higher energy level) Energy absorbed First shell (lowest energy level) Atomic nucleus (b) Energy lost

20. Electron Distribution and Chemical Properties The chemical behavior of an atom – determined by the distribution of electrons in electron shells The periodic table of the elements shows the electron distribution for each element Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

21. Fig. 2-9 Hydrogen 1 H Lithium 3 Li Beryllium 4 Be Boron 5 B Carbon 6 C Nitrogen 7 N Oxygen 8 O Fluorine 9 F Neon 10 Ne Helium 2 He Atomic number Element symbol Electron- distribution diagram Atomic mass 2 He 4.00 First shell Second shell Third shell Sodium 11 Na Magnesium 12 Mg Aluminum 13 Al Silicon 14 Si Phosphorus 15 P Sulfur 16 S Chlorine 17 Cl Argon 18 Ar

22. Valence electrons – those in the outermost shell, or valence shell – The chemical behavior of an atom is mostly determined by the valence electrons – Elements with a full valence shell are chemically inert Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

23. http://www.thecatalyst.org/elect abl.html

24. Electron Orbitals An orbital is – the three-dimensional space where an electron is found 90% of the time Each electron shell consists of a specific number of orbitals Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

25. Fig. 2-10-1 Electron-distribution diagram (a) Neon, with two filled shells (10 electrons) First shellSecond shell

26. Electron-distribution diagram (a) (b) Separate electron orbitals Neon, with two filled shells (10 electrons) First shellSecond shell 1s orbital Fig. 2-10-2

27. Electron-distribution diagram (a) (b) Separate electron orbitals Neon, with two filled shells (10 electrons) First shellSecond shell 1s orbital2s orbitalThree 2p orbitals x y z Fig. 2-10-3

28. Electron-distribution diagram (a) (b) Separate electron orbitals Neon, with two filled shells (10 electrons) First shellSecond shell 1s orbital2s orbitalThree 2p orbitals (c) Superimposed electron orbitals 1s, 2s, and 2p orbitals x y z Fig. 2-10-4

29. The formation and function of molecules depend on chemical bonding between atoms Atoms with incomplete valence shells share electrons with other atoms This results in a force of attractions called a covalent bond Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

30. Covalent Bonds A covalent bond – the sharing of a pair of valence electrons by two atoms the shared electrons count as part of each atom’s valence shell Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

31. Fig. 2-11 Hydrogen atoms (2 H) Hydrogen molecule (H 2 )

32. A molecule – two or more atoms held together by covalent bonds A single bond, is the sharing of one pair of electrons A double bond, is the sharing of two pairs of electrons Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

33. structural formula – H–H molecular formula – H 2 Animation: Covalent Bonds Animation: Covalent Bonds Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

34. Fig. 2-12a (a) Hydrogen (H 2 ) Name and Molecular Formula Electron- distribution Diagram Lewis Dot Structure and Structural Formula Space- filling Model

35. Fig. 2-12b (b) Oxygen (O 2 ) Name and Molecular Formula Electron- distribution Diagram Lewis Dot Structure and Structural Formula Space- filling Model

36. Fig. 2-12c (c) Water (H 2 O) Name and Molecular Formula Electron- distribution Diagram Lewis Dot Structure and Structural Formula Space- filling Model

37. Fig. 2-12d (d) Methane (CH 4 ) Name and Molecular Formula Electron- distribution Diagram Lewis Dot Structure and Structural Formula Space- filling Model

38. Covalent bonds – form between atoms of the same element or of different elements A compound – a combination of two or more different elements Bonding capacity is called the atom’s valence Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

39. Electronegativity – an atom’s attraction for the electrons in a covalent bond – The more electronegative an atom, the more strongly it pulls shared electrons toward itself Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

40. nonpolar covalent bond – Electrons are shared equally polar covalent bond – one atom is more electronegative – Electrons are not shared equally Unequal sharing of electrons – causes a partial positive or negative charge on the ends of a molecule Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

41. Fig. 2-13  – – ++ ++ H H O H2OH2O

42. Ionic Bonds Atoms sometimes strip electrons from their bonding partners – Example: the transfer of an electron from sodium to chlorine – After the transfer of an electron, both atoms have charges A charged atom (or molecule) is called an ion Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

43. Fig. 2-14-1 NaCl Na Sodium atom Chlorine atom Cl

44. Fig. 2-14-2 NaCl Na Cl Na Sodium atom Chlorine atom Cl Na + Sodium ion (a cation) Cl – Chloride ion (an anion) Sodium chloride (NaCl)

45. A cation is a positively charged ion An anion is a negatively charged ion An ionic bond is an attraction between an anion and a cation Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

46. Compounds formed by ionic bonds are called ionic compounds, or salts Salts, such as sodium chloride (table salt), are often found in nature as crystals Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

47. Fig. 2-15 Na + Cl –

48. Weak Chemical Bonds Strongest bonds in organisms – covalent bonds Weak chemical bonds are also important – ionic bonds – hydrogen bonds, Weak chemical bonds – reinforce shapes of large molecules – help molecules adhere to each other Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

49. Hydrogen Bonds A hydrogen bond – forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom – In living cells, the electronegative partners are usually oxygen or nitrogen atoms Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

50. Fig. 2-16    ++ ++    ++ ++ ++ Water (H 2 O) Ammonia (NH 3 ) Hydrogen bond

51. Van der Waals Interactions If electrons are distributed asymmetrically in molecules or atoms – result in “hot spots” of positive or negative charge Van der Waals interactions – attractions between molecules that are close together as a result of these charges Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

52. Collectively, such interactions can be strong, as between molecules of a gecko’s toe hairs and a wall surface Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

53. Molecular Shape and Function A molecule’s shape is very important to its function – determined by the positions of its atoms’ valence orbitals – the s and p orbitals may hybridize, creating specific molecular shapes Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

54. Fig. 2-17 s orbital Three p orbitals (a) Hybridization of orbitals Tetrahedron Four hybrid orbitals Space-filling Model Ball-and-stick Model Hybrid-orbital Model (with ball-and-stick model superimposed) Unbonded electron pair 104.5º Water (H 2 O) Methane (CH 4 ) (b) Molecular-shape models z x y

55. Fig. 2-17a s orbital z x y Three p orbitals Hybridization of orbitals Four hybrid orbitals Tetrahedron (a)

56. Fig. 2-17b Space-filling Model Ball-and-stick Model Hybrid-orbital Model (with ball-and-stick model superimposed) Unbonded electron pair 104.5º Water (H 2 O) Methane (CH 4 ) Molecular-shape models (b)

57. Biological molecules – Recognize and interact with each other with a specificity based on molecular shape – Molecules with similar shapes can have similar biological effects Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

58. Fig. 2-18a Natural endorphin Morphine Key Carbon Hydrogen Nitrogen Sulfur Oxygen Structures of endorphin and morphine (a)

59. Fig. 2-18b Natural endorphin Endorphin receptors Brain cell Binding to endorphin receptors Morphine (b)

60. Chemical reactions make and break chemical bonds Chemical reactions – the making and breaking of chemical bonds Reactants – the starting molecules of a chemical reaction Products – the final molecules of a chemical reaction Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

61. Fig. 2-UN2 ReactantsReactionProducts 2 H 2 O2O2 2 H 2 O

62. Photosynthesis is an important chemical reaction Sunlight powers the conversion of carbon dioxide and water to glucose and oxygen 6 CO 2 + 6 H 2 0 → C 6 H 12 O 6 + 6 O 2 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

63. Fig. 2-19

64. All chemical reactions are reversible: – products of the forward reaction become reactants for the reverse reaction Some chemical reactions go to completion: all reactants are converted to products Chemical equilibrium – reached when the forward and reverse reaction rates are equal Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

65. Fig. 2-UN3 Nucleus Protons (+ charge) determine element Neutrons (no charge) determine isotope Atom Electrons (– charge) form negative cloud and determine chemical behavior

66. Fig. 2-UN4

67. Fig. 2-UN5 Single covalent bond Double covalent bond

68. Fig. 2-UN6 Ionic bond Electron transfer forms ions Na Sodium atom Cl Chlorine atom Na + Sodium ion (a cation) Cl – Chloride ion (an anion)

69. Fig. 2-UN7

70. Fig. 2-UN8

71. Fig. 2-UN9

72. Fig. 2-UN10

73. Fig. 2-UN11

74. You should now be able to: 1.Identify the four major elements 2.Distinguish between the following pairs of terms: neutron and proton, atomic number and mass number, atomic weight and mass number 3.Distinguish between and discuss the biological importance of the following: nonpolar covalent bonds, polar covalent bonds, ionic bonds, hydrogen bonds, and van der Waals interactions Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings