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Chapter 2

Chapter 2. Chemical Foundations for Cells. Chapter Outline. Review of atomic structure Chemical bonding Ionic Covalent: nonpolar and polar Hydrogen “bonding” Properties of water Acids, bases, and buffers. Atomic Structure. Nucleus contains ____________

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Chapter 2

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  1. Chapter 2 Chemical Foundations for Cells

  2. Chapter Outline • Review of atomic structure • Chemical bonding • Ionic • Covalent: nonpolar and polar • Hydrogen “bonding” • Properties of water • Acids, bases, and buffers

  3. Atomic Structure • Nucleus contains ____________ • Electrons are found outside of the nucleus • In an atom the # of protons = # electrons • Some electron arrangements are more stable than others…….

  4. Chemical Bonding • Chemical bonding – atoms gain, lose, or share electron(s) to obtain a stable number of electrons

  5. Chemical Bonding • There are two types of bonds: • Ionic bonds • Covalent bonds • May be polar or nonpolar

  6. Chemical Bonding • Ionic Bond – strong attractive force between oppositely charged ions • Atoms form ions by losing or gaining enough electron(s) to obtain a stable # of electrons in their outer shell

  7. Chemical Bonding • Terms: • Cation – Positive ion, formed when an atom ____ electron(s) • Anion - Negative ion, formed when an atom ____ electron(s)

  8. Chemical Bonding • Covalent Bond – bonded atoms share pair(s) of electrons. • Occurs between ___________ • Examples: • H2 • O2 • H2 O

  9. Types of Covalent Bonds • Nonpolar covalent – bonded atoms share the electrons equally • Examples: • Polar Covalent – unequal pull on shared electrons by the bonded atoms • Examples:

  10. Hydrogen “Bonding” • Hydrogen “bond” – weak attractive force between a d + hydrogen bonded to an O, N or F atom and a d-O, N, or F in a second polar bond • Examples: • A hydrogen bond is not a true bond.

  11. Properties of Water • Water is a polar molecule capable of hydrogen bonding. • Related Terms: • Hydrophilic • Hydrophobic

  12. Properties of Water • Water resists changes in temperature. • When heat is applied to an aqueous solution much of the heat (energy) is used to break hydrogen bonds, not increase the movement of the molecules.

  13. Properties of Water • Water has a high surface tension – can also say, water is cohesive. • Cohesion – ability to resist rupturing when under tension

  14. Properties of Water • Water is a good solvent for ionic compounds and small polar molecules. • Water hydrates ions • Water hydrogen bonds to polar molecules

  15. Acids, Base, and Buffers • Many ions are dissolved in the fluids in/outside of cells • Na+, Ca+2, K+, • H+ • Level of each is critical • Focus on H+ (hydrogen ions)

  16. Acids, Base, and Buffers • Use the pH scale as a measure of the concentration of H+ in dilute solutions • See page 28 • Classify substances as acid, base or neutral by their pH • Acids: pH < 7 • Base: pH > 7 • Neutral: pH = 7

  17. Acids, Base, and Buffers • How the pH scale works • The lower the pH the more acidic • The higher the pH the more basic (alkaline) • A difference of 1 pH unit is a 10-fold difference in acidity or alkalinity

  18. Acids, Base, and Buffers • Acid: Substance that produces H+ when dissolved in water………. • Properties of Acids: • Corrosive • Sour if dilute enough to drink • Neutralize bases

  19. Acids, Base, and Buffers • Classifying Acids: • Strong acids ionize completely in water • Every acid molecule ionizes to form H+ • Example: • Weak Acids ionize slightly in water • Very few acid molecules form H+ in water • Examples:

  20. Acids, Base, and Buffers • Base: substance that produces OH-1 (hydroxide ion) in water • Examples: • Properties of bases • Corrosive • Bitter if dilute enough to drink • Neutralize acids

  21. Why is pH important? • Most cells require a pH near 7. Above or below this pH for too long and they die.

  22. Why is pH important? • Proteins function only at specific pHs. • pH needed depends upon where the protein needs to function • In lab you will determine the optimal pH for a protein that acts as an enzyme.

  23. Why is pH important? • Blood has a pH of 7.3 – 7.5* • If the pH is above or below this range for more than a couple of days death occurs. *a little higher than most give for the pH of blood

  24. Acids, Base, and Buffers • Buffers: solution that resists changes in pH even when acid or base is added • Buffers can both produce H+ and neutralize H+ • Most body solutions are buffered

  25. Buffers • Buffers are key to maintaining pH homeostasis • Buffers are made from weak acids and the ions they form in water • Ions formed act as bases in that they can neutralize (bind) H +

  26. Buffers • Blood buffer system see board and page 29

  27. Salts • Salts are ionic compounds that do not produce H+ or OH-1 when dissolved in water • Salt solutions are neutral

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