CH 2 - THE NATURE OF MOLECULES

  I. INTRO.

        A. Universe is made up of matter - solid, liquid & gas. 

              92 naturally occurring elements (p. 22)

        B. CHNOPS - 6 most common elements in organisms - 90% - 99% (p. 22)

        C. ELEMENTS = smallest unit of matter indivisible by ordinary chemical means. 

              ATOM = smallest particle of an element

       ATOMIC STRUCTURE - 3 parts (p. 19)

              1. Proton = (+) charge, in nucleus with a mass/weight of 1.

              2. Neutron = neutral charge, in nucleus with a mass/weight of1.

              3. Electron = (-) charge, orbitals around nucleus, mass is “0”.          

                    a. Atomic number = number of protons or electrons.

                    b. Atomic weight/mass = number of protons and neutrons.

                    c. The further from the nucleus (which energy level it occupies) the

                          is, the more energy it has. 

                    d. 1^st energy level holds 2 e^-, 2^nd & 3^rd hold 8 e^- each. (p. 21)

                    e. Atoms want to fill their outermost energy level, most stable, "happiest"

                    f. Chemical reactions involve interactions between outermost e^-

                          g. Valence = # of e^- in outermost energy level

        D. ISOTOPE = atom with a different # of neutrons than the average atom of an

                    element ( ₆C¹³ or ₆C¹⁴ instead of the usual ₆C¹²) (p. 19)

              1. Medicine - "tracers" - thallium in cardiology for blockage

              2. Research - N¹⁵ to follow path of nutrients in plants

        E. ION = charged atom (or molecule) due to addition or removal of e^-

      1. Cation = a positive ion (lost e^-)

            2. Anion = negative ion (gain e^-)

        3. Electrolytes = ions in bodily fluids, charged, elec. impulses

  II. CHEMICAL BONDS - join 2 or more atoms to from molecules, "MAGNETS"

        A. IONIC - One atom is a donor of an e^-, another is recipient of the e^-                                       

                    1. Strong in a solid and weak in a liquid.

              2. Breaking ionic bond produces ions (p. 23).

        B.  COVALENT - Sharing of one or more e^- between two atoms (p. 24).

              - strongest & most common bond in organic molecules

              1. Non-polar covalent - equal sharing of e^-   ex.  H₂.

              2. Polar Covalent - unequal sharing of e^-

                    a. e^- spends more time orbiting one atom than the other.  ex: H₂O (p. 26)

                    b. Electronegativity - atom with greater attraction for e^-

              3. Double Covalent - sharing of 2 e^- between 2 atoms, i.e. O₂

                    a. Triple Bond = sharing of three electrons, i.e. N₂

      C. HYDROGEN - between polar covalent molecules (p. 27)

        1. Due to attraction of unlike charges.

        2. Weak, but many together are very strong - H₂O

  III. BALANCED CHEMICAL EQUATIONS

        A. Reactants è Products

        B. Na +Cl = NaCl (Compound = 2 or more different elements held together)

        C. 2H₂ +O₂ = 2H₂O

        D. NaOH + HCl = NaCl + H₂O

  IV. WATER

        A. 70% of the world is water

        B. 50% to 95% of living organisms are made of water.

        C. Most chemical reactions happen in water (i.e. smell, taste, sight, reproduction)

  V. PROPERTIES OF WATER - CONSEQUENCES OF H-BONDS (p. 27 Table)

        A. WATER STRUCTURE (p. 26)

        B. SURFACE TENSION (p. 27)

              1. Cohesion = attraction of similar substance

              2. Adhesion = attraction of different substances

              3. Capillary action - water rising in a narrow tube (p. 27)

        C. RESISTANT TO TEMP. CHANGES - temperature buffer, stores heat

        D. HEAT OF VAPORIZATION - removes heat; sweat & cool off

        F. FREEZING - ice less dense than water so it floats!

              1. 4 H-bonds max, more stable

              2. Body of water freezes from the surface down - protects/insulates

  VI. WATER AS A SOLVENT - “universal solvent”

        A. SOLUTION = uniform mixture of 2 or more substances

              1. Solvent = liquid, present in greatest amount

              2. Solute = present in lesser amounts

        B. HYDROPHOBIC = "water fearing"           

              1. Electrically neutral

              2. Non-polar molecules

              3. Fats & oils

        C. HYDROPHYLLIC = "water loving"

              1. Electrically charged

              2. Polar molecules

              3. Ions, electrolytes & proteins

  VII. ACIDS & BASES (p. 29 & 30)

        A. IONIZATION of water molecules occurs due to them "bumping" into one another. 

              H₂O  èH⁺ + OH^-    (H⁺ is a proton) (OH^- hydroxide ion)

        B. pH = powers of Hydrogen = -log [H+] It ranges from 0 to 14. 

              1. Acid = pH<7 (ex. HCl è H⁺ + Cl^-). 

                    a. releases H+, increases [H+]

                    b. proton donor

                    c. strong acid has pH of 0,1 or 2, Hi [H+]

              2. Base = pH>7 (alkaline) (ex. NaOH è Na⁺ + OH^-)

                    a. Releases OH^-, decreases [H⁺]

                    b. proton acceptor . 

                    c. strong base 12,13,14, Low [H⁺]

              3. Blood pH is 7.35 to 7.45.

        C. BUFFER = chemical which can add or remove H⁺ to minimize pH changes.

              1. H₂O + CO₂ è H₂CO₃ è H⁺ + HCO₃^- (p. 30)