1. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Chapter 2 The Chemical Basis of Life

2. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Chemicals –Make up our bodies –Those of other organisms –The physical environment

3. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings ELEMENTS, ATOMS, AND MOLECULES 2.1 Living organisms are composed of about 25 chemical elements

4. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Carbon, Hydrogen, Oxygen, and Nitrogen Table 2.1

5. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Trace elements –Essential to life –Occur in minute amounts –common additives to food and water

6. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings CONNECTION Dietary deficiencies in trace elements –Can cause various physiological conditions Figure 2.2A

7. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Elements can combine to form compounds Sodium Chlorine Sodium Chloride Figure 2.3

8. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Concept 2.2: Atoms The smallest particle of matter that still retains the properties of an element Consist of Subatomic particles: –protons(+) –neutrons(0) –electrons(-)

9. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Protons and Neutrons –Located in a central nucleus Electrons –Arranged in electron shells surrounding nucleus Figure 2.4A + + –– + – 2 2 2 Protons Neutrons Electrons Mass number = 4 + + 2e – Electron cloud Nucleus Subatomic Particles

10. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings How does one element differ from another? = each element has a specific number of protons Helium Carbon

11. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings How does one element differ from another? = each element has a specific number of protons Helium Atomic # = 2 Carbon Atomic # = 4

12. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings How does one element differ from another? = each element has a specific number of protons Helium Mass # = 4 Carbon Mass # = 12

13. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Atomic Number and Atomic Mass Atoms of the various elements Differ in their number of subatomic particles

14. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Isotopes Number of neutrons in an atom may vary –Variant forms of an element are called isotopes –Some isotopes are radioactive Table 2.4

15. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings CONNECTION Radioactive isotopes can help or harm us Help: –tracers in basic biological research –medical diagnosis

16. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings EX: 4 Elements & Atomic/Mass Numbers #1. Which one of the following elements is NOT one of the 4 most abundant elements in living organisms? A. C B. HC. OD. KE. N #2. Nitrogen atom has 7 protons, and the most common isotope of nitrogen has 7 neutrons. A radioactive isotope of nitrogen has 9 neutrons. What is the atomic number and mass number of this radioactive nitrogen?

17. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Concept 2.3 Electron arrangement: Determines the chemical properties of an atom (how it behaves) Electron shells Figure 2.6

18. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Atoms whose shells are not full –interact with other atoms and gain, lose, or share electrons Interactions  Form chemical bonds Helium

19. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings EX: Electron Configuration & Ionic Bonding #3. Helium has an atomic number of 2. Hydrogen has an atomic number of 1. Which atom is more likely to react with other atoms? #4. Sodium has an atomic number of 11 and Chlorine has an atomic number of 17 a. Draw the electron configuration for the Sodium and Chlorine atoms b. How many electrons are in the outermost shell of each atom (valence electrons)?

20. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings What types of chemical bonds exist? 1.Ionic bond 2.Covalent bond: Nonpolar or Polar 3.Hydrogen bond

21. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 1. Ionic bonds: One atom gains electron(s) and another atom loses electron(s) –Charged atoms called ions are created Figure 2.7A Chemical Bonds

22. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Sodium and chloride ions –Bond to form sodium chloride, common table salt Na + Cl – Figure 2.7B

23. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 2. Covalent bonds: atoms share electrons –Two atoms share one or more pairs of outer shell electrons = molecules

24. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Table 2.8

25. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Equal vs. Unequal electron sharing Nonpolar covalent bond –Atoms share electrons equally Polar covalent bond –Atoms share electrons unequally

26. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings EX: Non-Polar Covalent Bonding #5. Hydrogen has an atomic number of 1. a.Draw the electron configuration for the Hydrogen atom. b.How many electrons are in the outermost shell of the atom (valence electrons)? c.Hydrogen covalently bonds with other hydrogen atoms to form a molecule. Based on the number of valence electrons in Hydrogen, predict the molecular formula of this molecule.

27. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings EX: Polar Covalent Bonding #6. Oxygen has an atomic number of 8 and Hydrogen has an atomic number of 1. a.Draw the electron configuration for the Oxygen and Hydrogen atoms b.How many electrons are in the outermost shell of each atom (valence electrons)? c.Oxygen covalently bonds with Hydrogen to form a molecule. Based on the number of valence electrons in Oxygen and Hydrogen, predict the molecular formula of this molecule.

28. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Polar covalent bond Ex: water molecule

29. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 3. Hydrogen bonds: - weak bonds - important in the chemistry of life Ex: The charged regions on water molecules –attracted to the oppositely charged regions on nearby molecules

30. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Hydrogen Bonds between water molecules Figure 2.10

31. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings CHEMICAL REACTIONS Concept 2.4 Chemical reactions In a chemical reaction –Reactants interact, atoms rearrange, and products result 2 H 2 O2O2 2 H 2 O Figure 2.17A

32. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Chemical Equilibrium: Rate of forward reaction equal to reverse reaction 2 H 2 O2O2 2 H 2 O

33. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Review Ch. 2: Living organisms made of ~25 elements Top 4 elements? Atom- protons, electrons, neutrons Atomic number vs. Mass number? How do Isotopes of an element differ? Draw Electron configuration: Sulfur (16) and Hydrogen (1)

34. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Review: Ch. 2 Valence electrons  Chemical bonding What types of chemical bonds exist? 1.Ionic bond 2.Covalent bond: Nonpolar or Polar 3.Hydrogen bond