1. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. BIOLOGY A GUIDE TO THE NATURAL WORLD FOURTH EDITION DAVID KROGH Fundamental Building Blocks: Chemistry, Water, and pH

2. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. 2.1 Chemistry’s Building Block: The Atom

3. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Chemistry’s Building Block: The Atom The fundamental unit of matter is the atom.

4. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Protons, Neurons, and Electrons The three most important constituent parts of an atom are –In the nucleus: protons (positive) neutrons (neutral) –Floating around the nucleus electrons (negative)

5. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Chapter 2 Lecture Figure 2.2 electron shell electron (negative charge) proton (positive charge) neutron (no charge) nucleus Hydrogen (H)Helium (He)

6. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. The Element An element is any substance that cannot be reduced to any simpler set of constituent substances through chemical means. Each element is defined by the number of protons in its nucleus.

7. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. 2.2 Matter is Transformed Through Chemical Bonding

8. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Matter is Transformed Through Chemical Bonding Atoms can link to one another in the process of chemical bonding.

9. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Covalent Bond Covalent bond: atoms share one or more electrons Ionic bond: atoms lose and accept electrons from each other

10. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Covalent Bond A molecule is a compound of a defined number of atoms in a defined spatial relationship. For example, two hydrogen atoms can link with one oxygen atom to form one water molecule.

11. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Covalent Bond Figure 2.8 hydrogen (H) atom hydrogen (H) atom oxygen (O) atom hydrogen (H) atom hydrogen (H) atom oxygen (O) atom (b) One water molecule (a) Two hydrogen atoms and one oxygen atom

12. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Covalent Bond Atoms of different elements differ in their power to attract electrons. The term for measuring this power is electronegativity.

13. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Polar and Nonpolar Bonding Through electronegativity, a molecule can take on a polarity—a difference in electrical charge at one end compared to the other.

14. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Polar and Nonpolar Bonding Covalent chemical bonds can be polar or nonpolar. A polar covalent bond exists when shared electrons are not shared equally among atoms in a molecule, due to electronegativity differences.

15. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Polar and Nonpolar Bonding Figure 2.9 polar nonpolar because charges are symmetric slight negative charge slight positive charge (a) Polar water molecule (b) Nonpolar methane molecule

16. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Ionic Bonding Two atoms will undergo a process of ionization when the electronegativity differences between them are great enough that one atom loses one or more electrons to the other. This process creates ions: atoms whose number of electrons differs from their number of protons.

17. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Ionic Bonding The charge differences that result from ionization can produce an electrostatic attraction between ions. This attraction is an ionic bond. When atoms of two or more elements bond together ionically, the result is an ionic compound.

18. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Ionic Bonding Figure 2.10 sodium atom (Na)chlorine atom (Cl) chloride ion (Cl – ) sodium ion (Na + ) electron transfer ionic compound (Na + Cl – ) salt crystals (a) Initial instability Sodium has but a single electron in its outer shell, while chlorine has seven, meaning it lacks only a single electron to have a completed outer shell. (b) Electron transfer When these two atoms come together, sodium loses its third-shell electron to chlorine, in the process becoming a sodium ion with a net positive charge (because it now has more protons than electrons). Having gained an electron, the chlorine atom becomes a chloride ion, with a net negative charge (because it has more electrons than protons). (c) Ionic attraction The sodium and chloride ions are now attracted to each other because they are oppositely charged. (d) Compound formation The result of this electrostatic attraction, involving many sodium and chloride ions, is a sodium chloride crystal (NaCl), better known as table salt.

19. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Hydrogen Bonding Hydrogen bonding links an already covalently bonded hydrogen atom with an electronegative atom.

20. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Hydrogen Bonding In water, a hydrogen atom of one water molecule will form a hydrogen bond with an unshared oxygen electron of a neighboring water molecule.

21. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Hydrogen Bonding Figure 2.11 hydrogen bond

22. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. 2.3 Some Qualities of Chemical Compounds

23. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Some Qualities of Chemical Compounds The three-dimensional molecular shape is important in biology because it determines the capacity molecules have to bind with one another.

24. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Molecular Shape Figure 2.13 good fit, scent is smelled signal to brain receptor molecules cells of nasal passage signal molecules (aroma from bread) bad fit, scent is not smelled

25. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. 2.4 Water and Life

26. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Water and Life Water has several qualities that have strongly affected life on Earth.

27. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Water is a Major Player in Many of Life’s Processes A solution is a homogeneous mixture of two or more kinds of molecules, atoms, or ions. The compound dissolved in solution is the solute; the compound doing the dissolving is the solvent.

28. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Water is a Major Player in Many of Life’s Processes Figure 2.15 water (solvent) sodium chloride (solute) Sodium and chloride ions dissolved in water Sodium chloride’s positively charged sodium ions (Na + ) are attracted to water’s negatively charged oxygen atoms, while its negatively charged chloride ions (Cl – ) are attracted to water’s positively charged hydrogen atoms. Pulled from the crystal, and separated from each other by this attraction, sodium and chloride ions become surrounded by water molecules. This process of separating sodium and chloride ions repeats until both ions are evenly dispersed, making this an aqueous solution. (a) Attraction (b) Separation (c) Dispersion O H H Cl – Na +

29. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Water is a Major Player in Many of Life’s Processes Water is a powerful solvent, with the ability to dissolve more compounds in greater amounts than any other liquid.

30. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Water’s Structure Gives It Many Unusual Properties Because water’s solid form (ice) is less dense than its liquid form, bodies of water in colder climates do not freeze solid in winter. Allows life to flourish under the ice.

31. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Water’s Structure Gives It Many Unusual Properties Figure 2.16 ice liquid water In ice, the maximum number of hydrogen bonds form, causing the molecules to be spread far apart. In liquid water, hydrogen bonds constantly break and re-form, enabling a more dense spacing than in ice.

32. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Water’s Structure Gives It Many Unusual Properties Water has a great capacity to absorb and retain heat. Because of this, the oceans act as heat buffers for the Earth, thus stabilizing Earth’s temperature.

33. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Water’s Structure Gives It Many Unusual Properties Water has a high degree of cohesion, which allows water to be drawn up through plants, via evaporation, in one continuous column, from roots through leaves.

34. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Hydrophobic and Hydrophilic Some compounds do not interact with water. Hydrocarbons such as petroleum are examples of such hydrophobic compounds. Water cannot break down hydrophobic compounds, which is why oil and water don’t mix.

35. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Hydrophobic and Hydrophilic Figure 2.17

36. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Hydrophobic and Hydrophilic Compounds that interact with water are polar or carry an electric charge and are called hydrophilic compounds.

37. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. 2.5 Acids and Bases Are Important to Life

38. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Acids and Bases Figure 2.18 acid base NaOH HCl (H 2 O) (a) Starting with pure water (b) Making water more acidic (c) Making water more basic (d) Combining acidic and basic solutions neutralized solution Hydrochloric acid (HCl), poured into the water, dissociates into H + and Cl - ions. With a higher concentration of H + ions in it, the water moves towards the acidic end of the pH scale. When the acid and base solutions are poured together, the OH – ions from (c) accept the H + ions from (b), forming water and keeping the solution at a neutral pH. An equal concentration of sodium hydroxide, poured into water, dissociates into Na + and OH – ions, moving the water toward the basic end of the scale. Pure water is a “neutral” substance in terms of its pH levels. pure water

39. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Acids and Bases The concentration of hydrogen ions that a given solution has determines how basic or acidic that solution is. The pH scale measures acidity. –This scale runs from 0 to 14, with 0 most acidic,14 the most basic, and 7 neutral.

40. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Acids and Bases Figure 2.19 hydrochloric acid lemon juice, gastric (stomach) juice cola, beer, wine, vinegar tomatoes black coffee urine water seawater baking soda Great Salt Lake household ammonia household bleach oven cleaner lye battery acid human blood is slightly basic human blood basic acidic pH H + concentration (moles/liter) neutral

41. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Acids and Bases The pH scale is logarithmic. –A substance with a pH of 9 is 10 times as basic as a substance with a pH of 8

42. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Acids and Bases Living things function best in a near-neutral pH, although some systems in living things have different pH requirements.