1. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies The Chemical Basis of Life (Pt.1) Chapter 2 Copyright © McGraw-Hill Companies Permission required for reproduction or display

2. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Atoms Any substance that has mass and occupies space is known as matter.  Composed of atoms. - Orbiting cloud of electrons. - Dense nucleus formed of protons (+) and neutrons.  Number of protons determines chemical character because it dictates number of electrons available for chemical activity.

3. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

4. 4 Atomic Number & Atomic Mass Atoms of the various elements Differ in their number of subatomic particles The number of protons in the nucleus = atomic number The number of protons + neutrons = atomic mass Neutral atoms have equal numbers of protons & electrons (+ and – charges)

5. 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

6. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Atoms Atomic Mass  Measured in daltons. - Protons and neutrons both weigh approximately 1 dalton, while electrons weigh 1/1840 of a dalton. - 602 million million billion daltons (6.02 X 10 to the 23 rd power) = 1 gram!!!

7. 7 Energy  Is defined as the capacity to do work causing change Potential energy - Is the energy that matter possesses because of its location or structure Kinetic Energy - Is the energy of motion

8. 8 Energy Levels of Electrons An atom’s electrons Vary in the amount of energy they possess Electrons further from the nucleus have more energy Electron’s can absorb energy and become “excited” Excited electrons gain energy and move to higher energy levels or lose energy and move to lower levels

9. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Atoms The atomic number (number of protons) of atoms of a particular element identifies the kind of element it is.  Atoms of an element that possess a different number of neutrons are called isotopes. - Some are unstable and spontaneously emit energetic subatomic particles.  Radioactive Decay  Half-Life

10. 10 Isotopes Different forms of the same element Have the same number of protons, but different number of neutrons May be radioactive spontaneously giving off particles and energy May be used to date fossils, in medicine, etc.

11. 11 Example of Isotope Use  Can be used in medicine to treat tumors Cancerous throat tissue Figure 2.6

12. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Atoms Electrons - Atoms with the same number of protons and electrons are electrically neutral.  Electrons are maintained in orbits by their attraction to the positively charged nucleus. - Ions - Atoms in which the number of electrons does not equal the number of protons.

13. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Chemical Behavior of Atoms Orbital - Area around a nucleus where an electron is most likely to be found. Because electrons are attracted to the nucleus, it takes energy to maintain them in orbitals.  Contain potential energy due to relative position.

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15. 15 Elements 92 naturally occurring elements. Can’t be broken down into simpler substances by chemical reaction Composed of atoms

16. 16 Properties of Matter An element’s properties depend on the structure of its atoms Each element consists of a certain kind of atom that is different from those of other elements An atom is the smallest unit of matter that still retains the properties of an element

17. Essential Elements of Life About 25 of the 92 elements are essential to 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

18. Table 2-1

19. 19 Trace Elements Trace elements Are required by an organism in only minute quantities Minerals such as Fe and Zn are trace elements

20. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Kinds of Atoms For most atoms, the outer energy level contains a maximum of eight electrons.  Octet Rule - Atoms tend to establish completely full outer energy levels. - Inert - Elements possessing a full complement of electrons in the outer shell. - Reactive - Atoms lacking a full complement of electrons in the outer shell.

21. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Chemical Behavior of Atoms Oxidation-Reduction (Redox) Reactions.  Oxidation - Loss of an electron.  Reduction – Gain of an electron.

22. 22 Molecules and Compounds Sodium + Chlorine yields Sodium Chloride + Molecules: Atoms held together by energy (chemical bonds) Ex. H-H, O-O Compounds: substances consisting of two or more elements combined in a fixed ratio Compounds have characteristics different from those of their elements Figure 2.2

23. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Ionic Bonds - Formation of Salts Ionic bonds form when atoms of opposite electrical charges attract each other.  Donation of an electron.

24. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Covalent Bonds Covalent bonds form when two atoms share one or more pairs of valence electrons.

25. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Covalent Bonds Bond Strength  Strength of a bond depends on the number of shared electrons. - Single Bond - Double Bond - Triple Bond

26. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Chemical Reactions Chemical Reactions occur because of the formation and breaking of chemical bonds leading to a change in the composition of matter  Reactants - Original molecules.  Products - Resultant molecules. Chemical reactions influenced by:  Temperature  Concentration of Reactants and Products  Catalysts

27. 27 Chemical Reactions Reactants Product 2 H 2 O2O2 2 H 2 O + + Chemical reactions  Convert reactants to products

28. 28 Chemical Reactions Photosynthesis  Is an example of a chemical reaction Figure 2.18

29. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Chemistry of Water Water molecule consists of an oxygen atom bound to two hydrogen atoms by two single covalent bonds. Copyright © McGraw-Hill Companies Permission required for reproduction or display

30. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Hydrogen Bonds In a water molecule, both oxygen and hydrogen atoms attract shared electrons in the covalent bonds (electronegativity).  Shared electrons are thus more likely to be found near the oxygen nucleus than near the hydrogen nuclei. - Polar Molecule - Has distinct ends, each with a partial charge.

31. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Four Emergent Properties of Water Polarity of water causes it to be attracted to other polar molecules.  Cohesion - Attraction to other water molecules. - Responsible for surface tension.  Water is adhesive to any substance with which it can form hydrogen bonds.  Adhesion - Attraction to other substance.

32. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Copyright © McGraw-Hill Companies Permission required for reproduction or display

33. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Properties of Water Heat Storage - Because of the large number of hydrogen bonds, a large input of thermal energy is necessary to break apart water molecules.  High Specific Heat (extent a substance resists changing temperature as it absorbs or loses heat).  High Heat of Vaporization (energy required to change liquid water to gas). - Sweating

34. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Properties of Water Solvent - Water is an effective solvent because of its ability to form hydrogen bonds.  Water molecules gather around any substance bearing an electrical charge.

35. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

36. Properties of Water Organization of Nonpolar Molecules - Water molecules act to exclude nonpolar molecules.  Hydrophobic - Nonpolar molecules shrink from contact with water. - (Water Hating)  Hydrophilic - Polar molecules readily form hydrogen bonds with water. - (Water Loving)

37. electrolytes: substances that break up or “dissociate” in solution to form charged particles (ions). cation: positive charge anion - Net negative charge.

38. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Water Ionizes Ionization - Spontaneous ion formation. pH Scale - Measures negative logarithm of hydrogen ion concentration in the solution.  Acids - Substances that dissociate in water to increase concentration of H + ions (cations) - pH values below 7.  Bases - Substances that combines with H + ions when dissolved in water and shift the H+ balance to OH – (anions) - pH values above 7.

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40. Water Ionizes Buffers– Weak acids or bases that act as a reservoir for hydrogen atoms to minimize change in pH pH of the fluids within most cells in a human is 6.5 – 7.5  Donates hydrogen atoms to the solution when their concentration falls, and removes them from the solution when their concentration rises.

41. Systems of Biochemical Buffers Dihydrogen phosphate system: - maintains pH in internal fluid of cells - controlled by the kidneys (excess hydrogen carbonate ions are excreted in the urine) Carbonic acid and hydrogen carbonate ion system: - maintains pH in blood - controlled by the lungs (respiration) - carbonic acid is in equilibrium with dissolved carbon dioxide gas