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Chapter 2: Chemistry (!) In many ways, life can be viewed as a complicated chemical reaction. Modern models of how life works at all levels typically have at least some aspect of chemistry as a major component or underpinning. Therefore…. You must understand chemistry to understand life (and to pass this course)! . Chapter 2: Chemistry Elements and Atoms Describing Atomic Combinations Chemical Bonds Hold Molecules Together and Store Energy Chemical Equations Describe Chemical Reactions Oxidation-Reduction Reactions (redox reactions) Are Common in Biological Systems . Chapter 2: Chemistry Elements and Atoms Describing Atomic Combinations Chemical Bonds Hold Molecules Together and Store Energy Chemical Equations Describe Chemical Reactions Oxidation-Reduction Reactions (redox reactions) Are Common in Biological Systems . • Describe the difference between the terms “element” and “atom”. • What are chemical symbols, and what is the periodic table? • Draw a model of a neutral atom with atomic number 6 and atomic mass 12. . Elements and Atoms http://serc.carleton.edu/images/usingdata/nasaimages/periodic-table.gif . Elements and Atoms elements – substances that cannot be further broken down into other substances (at least by ordinary chemical reactions) every element has a chemical symbol (H for hydrogen, O for oxygen, etc.); this is most familiar from the periodic table there are 92 naturally occurring elements, from hydrogen up to uranium http://serc.carleton.edu/images/usingdata/nasaimages/periodic-table.gif . Elements and Atoms O, C, H, N ~ 96% of living mass Ca, P, K, S, Na, Cl, Mg, Fe - consistently present in small amounts several trace elements . Elements and Atoms atom = smallest unit of an element electron: little mass; -1 proton: ~1 mass unit; +1 neutron : ~1 mass unit nucleus: protons and neutrons . Elements and Atoms atomic number = # of protons periodic table arranged largely according to atomic number . Elements and Atoms atomic mass ≈ protons + neutrons isotopes:# of protons same, # of neutrons different . • Describe the difference between the terms “element” and “atom”. • What are chemical symbols, and what is the periodic table? • Draw a model of a neutral atom with atomic number 6 and atomic mass 12. . • Draw a model of a neutral atom with atomic number 6 and atomic mass 14. • Compare with the previous atom that you drew and discuss isotopes. . Fig. 2.3 . Elements and Atoms atomic decay alpha, beta, and/or gamma radiation many uses and dangers DNA mutations decay rates are averages used for measuring time radioisotopes: most unstable isotopes . • Draw a model of a neutral atom with atomic number 6 and atomic mass 14. • Compare with the previous atom that you drew and discuss isotopes. . • What are electron orbitals? • What is the valence shell? • How does the valence shell relate to chemical reactivity of an atom? . Elements and Atoms electrons occupy orbitals ATOMS: # of electrons = # of protons orbitals: electrons energy levels, location probabilities electron shell: orbitals with similar energies . Elements and Atoms . Elements and Atoms valence shell: filled by highest-energy electrons valence electrons involved in chemical interactions “rule of eight” . • What are electron orbitals? • What is the valence shell? • How does the valence shell relate to chemical reactivity of an atom? . Chapter 2: Chemistry Elements and Atoms Describing Atomic Combinations Chemical Bonds Hold Molecules Together and Store Energy Chemical Equations Describe Chemical Reactions Oxidation-Reduction Reactions (redox reactions) Are Common in Biological Systems . • Draw a Venn diagram for the following terms: molecule compound • Then place the following in the diagram: O2 NaCl H2O . Describing Atomic Combinations molecule – has covalent bonds one or more elements examples: O2, H2O smallest unit of a molecular substance differs in properties from its elements . Describing Atomic Combinations compound - two or more different elements combined may just be ratios, not fixed numbers differs in properties from its elements may have ionic bonds . Describing Atomic Combinations chemical formula - number of atoms of each element molecular formula for molecules examples: H2O, CO2, O2, C6H12O6 simplest ratio for ionic compounds (NaCl, etc.) structural formula - arrangement of atoms examples: water H─O─H carbon dioxide O═C═O molecular oxygen O═O . • Draw a Venn diagram for the following terms: molecule compound • Then place the following in the diagram: O2 NaCl H2O . • Discuss moles, atomic mass units, and Avogadro’s number. • Why use moles instead of just mass? • Discuss the water and glucose problem (will be given in class). . Describing Atomic Combinations molecular mass = sum of the atomic masses in molecule mole: # molecules for gram amount to = atomic mass Example: water has molecular mass 1+1+16 = 18 mole of water has a mass of 18 g mole is simply a conversion factor Avogadro’s number, is 6.02 x 1023 atoms or molecules . • Discuss moles, atomic mass units, and Avogadro’s number. • Why use moles instead of just mass? • Discuss the water and glucose problem (will be given in class). . Chapter 2: Chemistry Elements and Atoms Describing Atomic Combinations Chemical Bonds Hold Molecules Together and Store Energy Chemical Equations Describe Chemical Reactions Oxidation-Reduction Reactions (redox reactions) Are Common in Biological Systems . • What is a covalent bond? • What do polar and nonpolar mean for covalent bonds? • Give an example of each. . Chemical Bonds Hold Molecules Together and Store Energy outermost shell (valence electrons) determine chemistry filled shells: rule of 8 . Chemical Bonds Hold Molecules Together and Store Energy chemical bonds are based on filling valence shells reduced energy state bond energy amount required to break bond . Chemical Bonds Hold Molecules Together and Store Energy strong chemical bonds covalent bonds – electrons shared ionic bonds – ions of opposite charge . Chemical Bonds Hold Molecules Together and Store Energy covalent bonds electrons shared in pairs 1 pair is a single covalent bond double and triple also possible carbon forms four total . Chemical Bonds Hold Molecules Together and Store Energy covalent bonds give definite shapes spacial arrangements of shared orbitals . Chemical Bonds Hold Molecules Together and Store Energy covalent bonds nonpolar: equal sharing polar: unequal sharing polar if one nucleus holds a stronger attraction on the electron pair polar molecules have regions with partial charges . • What is a covalent bond? • What do polar and nonpolar mean for covalent bonds? • Give an example of each. . • What are ions? • What are cations and anions? • What is an ionic bond? • Give an example of an ionic bond. . Chemical Bonds Hold Molecules Together and Store Energy ionic bonds ion: atom that has gained or lost at least one net electron cations - lost one or more; +charge anions - gained one or more; -charge –ide indicates an anion polyatomic ions can also form covalently bound atoms that lose or gain electrons or protons only polyatomic ions can lose or gain protons . Chemical Bonds Hold Molecules Together and Store Energy ionic bonds ionic bond: cation/anion attraction ionic compound: substance with ionic bonds . Chemical Bonds Hold Molecules Together and Store Energy ionic bonds polar substances, such as water, tend to dissolve ionic compounds hydration – surrounding ions with the ends water molecules with the opposite (partial) charge . • What are ions? • What are cations and anions? • What is an ionic bond? • Give an example of an ionic bond. . • What are hydrogen bonds? • Draw an example. . Chemical Bonds Hold Molecules Together and Store Energy hydrogen bonds d+ with d- d+ charge is usually H weak interaction . Chemical Bonds Hold Molecules Together and Store Energy hydrogen bonds common and important in living things water forms them weak means relatively easy to manipulate collectively, hydrogen bonds can be very strong – they hold together the two strands of DNA, for example . • What are hydrogen bonds? • Draw an example. . Chemical Bonds Hold Molecules Together and Store Energy In aqueous systems (such as living organisms), the effective relative bond strengths are: covalent bond > ionic bond > hydrogen bond . Chapter 2: Chemistry Elements and Atoms Describing Atomic Combinations Chemical Bonds Hold Molecules Together and Store Energy Chemical Equations Describe Chemical Reactions Oxidation-Reduction Reactions (redox reactions) Are Common in Biological Systems . • Discuss the chemical equations in the notes and the terms there (reactant, product, equilibrium). . Chemical Equations Describe Chemical Reactions Reactants are written on the left Products are written on the right an arrow ( ) is used to show the direction the reaction proceeds C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy double arrows ( ) indicate equilibrium reactions - i.e. reactions proceeding at simultaneously in both directions N2 + 3 H2 2 NH3 Sometimes, different lengths of double arrows are used to indicate which direction is favored CO2 + H2O H2CO3 . • Discuss the chemical equations in the notes and the terms there (reactant, product, equilibrium). . Chapter 2: Chemistry Elements and Atoms Describing Atomic Combinations Chemical Bonds Hold Molecules Together and Store Energy Chemical Equations Describe Chemical Reactions Oxidation-Reduction Reactions (redox reactions) Are Common in Biological Systems . • What is a redox reaction, and how does it relate to movement of electrons and movement of energy? • What gets oxidized/reduced in the following: – – • making NaCl rusting iron What gains/loses energy in each case? . . Oxidation-Reduction Reactions Are Common in Biological Systems example: rusting 4 Fe + 3 O2 during the process iron atoms (Fe) become iron ions (Fe3+): 4 Fe 2 Fe2O3 4 Fe3+ + 12 e- on the flip side, the oxygen atoms gain electrons 3 O2 + 12 e- 6 O2- . Oxidation-Reduction Reactions Are Common in Biological Systems oxygen is common oxidizing agent (hence “oxidation”) redox in biological systems very important in photosynthesis, respiration, more electrons are less easily lost from molecules than from atoms molecules typically will lose the equivalent of a complete hydrogen atom when oxidized (proton as well as electron) counting charge changes alone is not sufficient – look for movement of electrons , includes complete H equivalent . • What is a redox reaction, and how does it relate to movement of electrons and movement of energy? • What gets oxidized/reduced in the following: – – • making NaCl rusting iron What gains/loses energy in each case? .