BIO 101 1st EditionLecture 2Outline of Last LectureI. BiologyII. Structural LevelsIII. Emergent PropertiesIV. Cell TheoryV. Heritable InformationVI. Structure and FunctionVII. Unity in DiversityOutline of Current LectureI. Mattera. Elementb. CompoundII. Structure and Behavior of Atomsa. Atomic number b. Atomic massc. IsotopesIII. Electrons and EnergyIV. Chemical bondsa. Strong Bondsi. Covalent bondsii. Ionic bondsV. Chemical Reactionsa. Weak bondsChapter 2- Atoms, Molecules, and Chemical BondsI. Matter- elements and compounds, anything that takes up space and has massa. Element- can’t be broken into other substances by ordinary chemical means- 92 naturally occurring elements*25 required for life 4 elements make up 96% of living matter Carbon(C)Oxygen (O)Hydrogen (H)Nitrogen (N)b. Compound- molecules made of more than 1 element in a fixed ratioEx: NaCl (sodium chloride) [sodium (explosive metal)[chlorine (poison gas)This is an example of emergent property [NaCl] edible solid=table saltII. Structure and Behavior of Atoms - smallest possible amount of an elementa. All atoms of an element are alikeb. Each element has its own kind of atomsBIO 101 1st EditionEx: C and H are different from one anotherAtoms are made of subatomic particlesIn nucleus {protons: (+) charge, mass 1.7 * 10^-24g (1 dalton) { neutrons: no charge, mass (same as protons) orbit around nucleus {electrons: (-) charge, mass 1/2000 of proton or neutronex: of atom structure: H atom 1 proton C atom 6 protons 1 electron 6 neutrons 6 electronsAtomic Number= number of protons in an atomEx: atomic number of H= 1 *in a neutral atom (not charged) atomic number of C= 6 number of protons=number of electrons atomic number=number of electronsAtomic Mass= # of protons plus # of neutrons (ie how much an atom weighs)Symbols 12 superscript= atomic mass C symbol for element C 6 subscript= atomic numberIsotopes= atoms of an element that have different atomic mass but same atomic number (ie different number of neutrons)- Some are unstable= radioisotopes- Release energy as they break down- They can be usefulIII. Electrons and Energy Levels: where electrons are found-orbiting nucleus of atom- at discrete levels (positions) called shellsa. Electrons fill up closest shell first (2 electrons)b. Outer shells filled in order (next ones hold 8)c. If atom doesn’t have enough electrons to fill all shells, only outer most shell is partly emptyd. Octet rule: all atoms have tendency to fill up the outer shell (ex: noble elements)*chemical properties of an element depend on # of electrons in outermost shell*IV. Chemical bonds- attractions that hold atoms togethera. Molecule= 2 or more atoms held together by chemical bondsb. *valence*= bonding capacity of an atom = number of bonds an atom must form to be stable =number of electrons needed to fill outermost shellelement valenceH 1O 2BIO 101 1st EditionN 3C 4Strong BondsA. Covalent Bonds- a chemical bonds formed by sharing electrons: strong bond2 kinds: nonpolar- covalent polar- covalentnonpolar covalent bond- bond formed when two atoms with a similar or identical electronegativity share a pair of electrons*electronegativity*= ability to attract electrons0.9 2.1 2.5 3.0 3.0 3.5Na< H< C< N = Cl< OLow ability high ability to attract electronsnonpolar bond- 2 atoms share a pair of electrons equally because there isabout the same ability to attract the shared electronspolar covalent bond- share electrons unequally- One atom has a greater electronegativity- “it hogs up” the electronsand is a little bit negatively charged- Other atom is cheated out of shared electrons much of the time and a little bit positively charged- Usually find polar covalent bonds in molecules involving H with O, N, Clsingle covalent bonds= atoms share 1 pair of electronsdouble covalent bonds= atoms share 2 pairs of electronstriple covalent bonds= atoms share 3 pairs of electronsB. Ionic Bonds- bond formed by electrostatic attraction between two atoms after a complete transfer of an electron from a donor atom to an acceptor atom. Strong bond.Ex: NaCl [Na -1 electron in outer shell [Cl -7 electrons in outer shell [Na+Cl- charge attraction is ionic bondNa loses 1 electron, becomes Na+Cl gains electron, becomes Cl-BIO 101 1st EditionV. Chemical Reactions- the breaking and forming of chemical bonds described by chemical equations that tell what atoms are involved, how many, which way reaction goesex: 3H2 + N2 2NH3- Most biologically important reactions are reversible and reach an equilibrium (i.e. rate of forward reaction=rate of back reaction)Weak bonds- some are important for biologyHydrogen bond- weak charge attraction between a (+)H atom of one molecule and a (-) atom of another moleculeex: H20- No electron sharing- No electron transfer- Weak bond- 1/20 strength of covalent bond- Continually breaking and reformingWeak attraction between polar moleculesHydrophobic bond= tendency of nonpolar molecules to avoid H20 (a polar substance) and thus associate with each otherEx: important in membrane
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