1. © 2010 Pearson Education, Inc. Lectures by Chris C. Romero, updated by Edward J. Zalisko PowerPoint ® Lectures for Campbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean Dickey Campbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey Chapter 2 Essential Chemistry for Biology

2. © 2010 Pearson Education, Inc. Matter: Elements and Compounds Matter is anything that occupies space and has mass. Matter is found on the Earth in three physical states: –Solid –Liquid –Gas Matter is composed of chemical elements. –Elements are substances that cannot be broken down into other substances. –There are 92 naturally occurring elements on Earth. All of the elements are listed in the periodic table.

3. H Rb K Na Li Fr Cs Sr Ca Mg Be Ra Ba Y Sc Ac La Zr Ti Rf Hf Nb V Db Ta Mo Cr Sg W Tc Mn Bh Re Ru Fe Hs Os Rh Co Mt Ir Pd Ni Uun Pt Xe Kr Uuo Rn Ag Cu Uuu Au Cd Zn Uub Hg Ar Ne In Ga Tl Al B Sn Ge Uuq Pb Si C Sb As Bi P N Te Se Uuh Po S O I Br At Cl F He Th Ce Pa Pr U Nd Np Pm Pu Sm Am Eu Lr Lu Cm Gd Bk Tb Cf Dy Es Ho Fm Er Md Tm No Yb 6 C 12 Figure 2.1

4. © 2010 Pearson Education, Inc. Twenty-five elements are essential to life. Four elements make up about 96% of the weight of the human body: –Oxygen –Carbon –Hydrogen –Nitrogen

5. Carbon  C  : 18.5% Hydrogen  H  : 9.5% Nitrogen  N  : 3.3% Calcium  Ca  : 1.5% Trace elements: less than 0.01% Boron  B  Manganese  Mn  Oxygen  O  : 65.0% Magnesium  Mg  : 0.1% Phosphorus  P  : 1.0% Potassium  K  : 0.4% Sulfur  S  : 0.3% Sodium  Na  : 0.2% Chlorine  Cl  : 0.2% Cobalt  Co  Chromium  Cr  Iron  Fe  Iodine  I  Fluorine  F  Copper  Cu  Silicon  Si  Zinc  Zn  Vanadium  V  Tin  Sn  Molybdenum  Mo  Selenium  Se  Figure 2.2

6. Figure 2.3 Lack of iodine can cause goiter

7. © 2010 Pearson Education, Inc. Elements can combine to form compounds. –Compounds are substances that contain two or more elements in a fixed ratio. –Common compounds include –NaCl (table salt) –H 2 O (water)

8. © 2010 Pearson Education, Inc. Atoms Each element consists of one kind of atom. –An atom is the smallest unit of matter that still retains the properties of an element. Atoms are composed of subatomic particles. –A proton is positively charged. –An electron is negatively charged. –A neutron is electrically neutral.

9. © 2010 Pearson Education, Inc. Proton Positive charge Determines element Neutron No charge Determines isotope Electron Negative charge Participates in chemical reactions Outer-shell electrons determine chemical behavior Nucleus Consists of neutrons and protons Atom Figure UN2-5

10. © 2010 Pearson Education, Inc. Elements differ in the number of subatomic particles in their atoms. –The number of protons, the atomic number, determines which element it is. –An atom’s mass number is the sum of the number of protons and neutrons. –Mass is a measure of the amount of matter in an object.

11. First electron shell  can hold 2 electrons  Outer electron shell  can hold 8 electrons  Hydrogen  H  Atomic number = 1 Carbon  C  Atomic number = 6 Nitrogen  N  Atomic number = 7 Oxygen  O  Atomic number = 8 Electron Figure 2.5

12. © 2010 Pearson Education, Inc. Chemical Bonding and Molecules Chemical reactions enable atoms to give up or acquire electrons to complete their outer shells. Chemical reactions usually result in atoms –Staying close together –Being held together by chemical bonds When an atom loses or gains electrons, it becomes electrically charged. –Charged atoms are called ions. –Ionic bonds are formed between oppositely charged ions.

13. Outer shell has 1 electron Outer shell has 7 electrons The outer electron is stripped from sodium and completes the chlorine atom’s outer shell Na Sodium atom Cl Chlorine atom Complete outer shells The attraction between the ions—an ionic bond—holds them together Na  Sodium ion Cl  Chlorine ion Sodium chloride (NaCl) Figure 2.6-2

14. © 2010 Pearson Education, Inc. Covalent Bonds A covalent bond forms when two atoms share one or more pairs of outer-shell electrons. Atoms held together by covalent bonds form a molecule. The number of covalent bonds an atom can form is equal to the number of additional electrons needed to fill its outer shell.

15. Name  molecular formula  Hydrogen gas  H 2  Oxygen gas  O 2  Methane  CH 4  Electron configurationStructural formulaSpace-filling modelBall-and-stick model Single bond  a pair of shared electrons  Double bond  two pairs of shared electrons  Figure 2.7

16. © 2010 Pearson Education, Inc. Hydrogen Bonds Water is a compound in which the electrons in its covalent bonds are shared unequally. –This causes water to be a polar molecule, one with opposite charges on opposite ends.

17. HH O  slightly   slightly –  Figure UN2-2

18. © 2010 Pearson Education, Inc. The polarity of water results in weak electrical attractions between neighboring water molecules. –These interactions are called hydrogen bonds.

19. Hydrogen bond Figure 2.8

20. © 2010 Pearson Education, Inc. Water’s Life-Supporting Properties The polarity of water molecules and the hydrogen bonding that results explain most of water’s life-supporting properties. –Water molecules stick together. –Water has a strong resistance to change in temperature. –Frozen water floats. –Water is a common solvent for life.

21. Microscopic tubes Cohesion due to hydrogen bonds between water molecules Evaporation from the leaves SEM Flow of water Figure 2.10

22. Figure 2.11

23. © 2010 Pearson Education, Inc. Heat and temperature are related, but different. –Heat is the amount of energy associated with the movement of the atoms and molecules in a body of matter. –Temperature measures the intensity of heat. Water can absorb and store large amounts of heat while only changing a few degrees in temperature. Water can moderate temperatures. –Earth’s giant water supply causes temperatures to stay within limits that permit life. –Evaporative cooling removes heat from the Earth and from organisms.

24. © 2010 Pearson Education, Inc. The Biological Significance of Ice Floating When water molecules get cold enough, they move apart, forming ice. A chunk of ice has fewer molecules than an equal volume of liquid water. Ice floats because it is less dense than the liquid water around it. If ice did not float, ponds, lakes, and even the oceans would freeze solid. Life in water could not survive if bodies of water froze solid.

25. Hydrogen bond Liquid water Ice Figure 2.13

26. © 2010 Pearson Education, Inc. Water as the Solvent of Life A solution is a liquid consisting of a homogeneous mixture of two or more substances. –The dissolving agent is the solvent. –The dissolved substance is the solute. When water is the solvent, the result is an aqueous solution.

27. © 2010 Pearson Education, Inc. Acids, Bases, and pH A chemical compound that releases H + to solution is an acid. A compound that accepts H + and removes it from solution is a base. Buffers are substances that resist pH change. Buffers –Accept H + ions when they are in excess –Donate H + ions when they are depleted Increases in global CO 2 concentrations may lead to the acidification of the oceans. To describe the acidity of a solution, chemists use the pH scale.

28. Basic solution Neutral solution Acidic solution Oven cleaner Household bleach Human blood Pure water Grapefruit juice, soft drink Lemon juice, gastric juice Household ammonia Milk of magnesia Seawater Tomato juice Urine pH scale 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Increasingly acidic  greater H  concentration  Increasingly basic  lower H  concentration  Neutral [ H + ]  [ OH – ] Figure 2.16