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Chapter 2

Chapter 2. Chemistry Comes Alive. Part B. Polar and Nonpolar Molecules. Electrons shared equally between atoms produce nonpolar molecules Unequal sharing of electrons produces polar molecules Atoms with 6 or 7 valence shell electrons are electronegative

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Chapter 2

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  1. Chapter 2 Chemistry Comes Alive Part B

  2. Polar and Nonpolar Molecules • Electrons shared equally between atoms produce nonpolar molecules • Unequal sharing of electrons produces polar molecules • Atoms with 6 or 7 valence shell electrons are electronegative • Atoms with 1 or 2 valence shell electrons are electropositive

  3. Comparison of Ionic, Polar Covalent, and Nonpolar Covalent Bonds Figure 2.8

  4. Hydrogen Bonds • Too weak to bind atoms together • Common in dipoles such as water • Responsible for surface tension in water • Important as intramolecular bonds, giving the molecule a three-dimensional shape Figure 2.9

  5. Chemical Reactions • Occur when chemical bonds are formed, rearranged, or broken • Are written in symbolic form using chemical equations • Chemical equations contain: • Number and type of reacting substances, and products produced • Relative amounts of reactants and products H + H  H2 (reactants) (product)

  6. Patterns of Chemical Reactions • Combination reactions: Synthesis reactions which always involve bond formation • A + B  AB • Decomposition reactions: Molecules are broken down into smaller molecules • AB  A + B • Exchange reactions: Bonds are both made and broken • AB + C  AC + B

  7. Oxidation-Reduction (Redox) Reactions • Reactants losing electrons are electron donors and are oxidized • Reactants taking up electrons are electron acceptors and become reduced

  8. Energy Flow in Chemical Reactions • Exergonic reactions – reactions that release energy • Endergonic reactions – reactions whose products contain more potential energy than did its reactants

  9. Reversibility of Chemical Reactions • All chemical reactions are theoretically reversible A + B  AB AB  A + B • If neither a forward nor reverse reaction is dominant, chemical equilibrium is reached

  10. Factors Influencing Rate of Chemical Reactions • Temperature – chemical reactions proceed quicker at higher temperatures • Particle size – the smaller the particle the faster the chemical reaction • Concentration – higher reacting particle concentrations produce faster reactions • Catalysts – increase the rate of a reaction without being chemically changed • Enzymes – biological catalysts

  11. Biochemistry • Organic compounds • Contain carbon, are covalently bonded, and are often large • Inorganic compounds • Do not contain carbon • Water, salts, and many acids and bases

  12. Water • High heat capacity – absorbs and releases large amounts of heat before changing temperature • High heat of vaporization – changing from a liquid to a gas requires large amounts of heat • Polar solvent properties – dissolves ionic substances, forms hydration layers around large charged molecules, and serves as the body’s major transport medium • Reactivity – is an important part of hydrolysis and dehydration synthesis reactions • Cushioning – resilient cushion around certain body organs

  13. Salts • Inorganic compounds • Contain cations other than H+ and anions other than OH– • Are electrolytes; they conduct electrical currents

  14. Acids and Bases • Acids release H+ and are therefore proton donors HCl  H+ + Cl – • Bases release OH– and are proton receptors NaOH  Na+ + OH–

  15. Acid-Base Concentration (pH) • Acidic solutions have higher H+concentration and therefore a lower pH • Alkaline solutions have lower H+ concentration and therefore a higher pH • Neutral solutions have equal H+ and OH– concentrations

  16. Acid-Base Concentration (pH) • Acidic: pH 0–6.99 • Basic: pH 7.01–14 • Neutral: pH 7.00 Figure 2.12

  17. Buffers • Systems that resist abrupt and large swings in the pH of body fluids • Carbonic acid–bicarbonate system • Carbonic acid dissociates reversibly releasing bicarbonate ions and protons • The chemical equilibrium between carbonic acid and bicarbonate resists pH changes in the blood

  18. Organic Compounds • Carbohydrates • Lipids • Proteins • Nucleic Acids

  19. Carbohydrates • Contain carbon, hydrogen, and oxygen • Their major function is to supply a source of cellular food • Examples: • Monosaccharides or simple sugars Figure 2.13a

  20. Carbohydrates • Disaccharides or double sugars Figure 2.13b

  21. Carbohydrates • Polysaccharides or polymers of simple sugars Figure 2.13c

  22. Lipids • Contain C, H, and O, but the proportion of oxygen in lipids is less than in carbohydrates • Examples: • Neutral fats or triglycerides • Phospholipids • Steroids • Eicosanoids

  23. Neutral Fats (Triglycerides) • Composed of three fatty acids bonded to a glycerol molecule Figure 2.14a

  24. Other Lipids • Phospholipids – modified triglycerides with two fatty acid groups and a phosphorus group Figure 2.14b

  25. Other Lipids • Steroids – flat molecules with four interlocking hydrocarbon rings • Eicosanoids – 20-carbon fatty acids found in cell membranes Figure 2.14c

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