BIO 101 1st Edition Outline of Last Lecture I Biology II Structural Levels III Emergent Properties IV Cell Theory V Heritable Information VI Structure and Function VII Unity in Diversity Lecture 2 Outline of Current Lecture I Matter a Element b Compound II Structure and Behavior of Atoms a Atomic number b Atomic mass c Isotopes III Electrons and Energy IV Chemical bonds a Strong Bonds i Covalent bonds ii Ionic bonds V Chemical Reactions a Weak bonds Chapter 2 Atoms Molecules and Chemical Bonds I Matter elements and compounds anything that takes up space and has mass a 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 ratio Ex NaCl sodium chloride sodium explosive metal chlorine poison gas This is an example of emergent property NaCl edible solid table salt II Structure and Behavior of Atoms smallest possible amount of an element a All atoms of an element are alike b Each element has its own kind of atoms BIO 101 1st Edition Ex C and H are different from one another Atoms are made of subatomic particles In 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 neutron ex of atom structure H atom 1 proton C atom 6 protons 1 electron 6 neutrons 6 electrons Atomic Number number of protons in an atom Ex 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 electrons Atomic 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 number Isotopes 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 useful III Electrons and Energy Levels where electrons are found orbiting nucleus of atom at discrete levels positions called shells a 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 empty d 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 together a Molecule 2 or more atoms held together by chemical bonds b valence bonding capacity of an atom number of bonds an atom must form to be stable number of electrons needed to fill outermost shell valence 1 2 element H O BIO 101 1st Edition N C 3 4 Strong Bonds A Covalent Bonds a chemical bonds formed by sharing electrons strong bond 2 kinds nonpolar covalent polar covalent nonpolar covalent bond bond formed when two atoms with a similar or identical electronegativity share a pair of electrons electronegativity ability to attract electrons 0 9 2 1 2 5 3 0 3 0 3 5 Na H C N Cl O Low ability high ability to attract electrons nonpolar bond 2 atoms share a pair of electrons equally because there is about the same ability to attract the shared electrons polar covalent bond share electrons unequally One atom has a greater electronegativity it hogs up the electrons and 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 Cl single covalent bonds atoms share 1 pair of electrons double covalent bonds atoms share 2 pairs of electrons triple covalent bonds atoms share 3 pairs of electrons B 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 bond Na loses 1 electron becomes Na Cl gains electron becomes Cl BIO 101 1st Edition V Chemical Reactions the breaking and forming of chemical bonds described by chemical equations that tell what atoms are involved how many which way reaction goes ex 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 biology Hydrogen bond weak charge attraction between a H atom of one molecule and a atom of another molecule ex H20 No electron sharing No electron transfer Weak bond 1 20 strength of covalent bond Continually breaking and reforming Weak attraction between polar molecules Hydrophobic bond tendency of nonpolar molecules to avoid H20 a polar substance and thus associate with each other Ex important in membrane structure
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