Chapter 2- The Nature of Molecules
Look at ALL of the figures EXCEPT 2.19 and 2.20, and read the figure legends for comprehension. That means that if you have a question about the figure after you have read the legend, you should look in the text for further explanation, or ask for clarification from me or another student in the class.
***************************************************************
lecture notes:
matter- occupies space and has mass composed of atoms atom nucleus protons (+) & neutrons # protons determines atomic number electrons (-) usually one per proton atomic mass = # protons + # neutrons (each ~ 1 dalton) electrons weigh much less (mass is same regardless of gravitation, weight changes with gravity) element- (behavior determined by # protons) any substance that cannot be broken down to any other substance by ordinary chemical means isotope- same element with different # neutrons some elements (like carbon) have several naturally- occurring isotopes some are unstable break down to lower elements = radioactive decay radioactive isotopes different stabilities but decay of isotope is constant half-life (half atoms in sample to decay) 14C is 5600 years used to date rocks & fossils ions-atoms whose electrons don't equal protons cation (positive charge) fewer electrons anion (negative charge) more electrons # electrons determines behavior of atoms orbital area where electron likely to be found can only contain 2 electrons has different levels (energy levels) 1,2 has different shapes s, p potential energy- based on position electron farther from nucleus, more p. energy move to higher orbital example: how chloraphyll capture energy oxidation- loss of electron to another atom reduction- gain of electron from another atom Periodic Table: 92 naturally occurring elements patterns of chemical properties repeated in groups of 8 due to valence electrons (out ring of orbitals) those that have all outer electorns are inert those with 1 or 7 are highly reactive behavior of atoms therefore predictable 4 are common in living bodies oxygen, hydrogen, carbon & nitrogen not the same proportion as earth's crust Chemical bonds hold atoms together (molecule) Ionic bonds atoms of opposite charges attract Na+ Cl- to form table salt crystals bonds not betw particular ions Covalent bonds when two atoms share electron pairs stable bonds no net charge octet rule is satisfied no free electrons betw two particular ions single bonds atoms share one electron weaker bond double bonds atoms share two electrons stronger bond WATER only molecule to exist as liquid at earth's temps influenced evolution of life due to it's presence stable molecular structure: held together by covalent bonds one oxygen two hydrogens forms a polar molecule electrons more drawn to O has slight negative charge (d-) Hs have slight positive charge results in tetrahedral shape analogy: polar ends like a magnet one of the most polar molecules known polar molecules interact with each other d- attracted to d+ of other molecule known as hydrogen bonds (often involve hydrogen) weak & transient but powerful cumulatively cohesion water molecule attracted to other water adhesion water molecule attracted to diff polar subst. e.g., glass water stores heat H bonds absorb heat when broken H bonds release heat when formed water forms many H bonds, so it takes a lot of heat to break enough H bonds to make water evaporate water has high specific heat heat absorbed or lost to change temp by 1 degree C therefore organisms hold temp well (mostly water) also high heat of vaporization power of evaporative cooling water is a solvent because of H bonds hydration shells form around molecules both ions and polar molecules water excludes nonpolar molecules (like oil) makes them associate water ionizes to make H+ and OH- at r.t. 10-7 mole of H+ ions pH = -log[H+] = 7 pH is a log scale since there are an equal # OH-, it's neutral anything that contributes H+ is an acid anything that binds to H+ is a base