BIOL 101 1st Edition Lecture 2 Outline of Last Lecture I What is Biology II III Unifying Themes of Biology Diversity and Unity in Life Outline of Current Lecture I Matter II Structure and Behavior of Atoms III Electrons and Energy Levels IV Chemical Bonds V Chemical Reactions Current Lecture Chapter 2 Atoms Molecules and Chemical Bonds basic inorganic chemistry I Matter takes up space and has mass elements and compounds a Elements can t be broken down into other substances by normal chemical processes 1 Carbon C 2 Oxygen O 3 Hydrogen H 4 Nitrogen N b Compound molecules made of more than 1 element in a fixed ratio Ex NaCl Sodium Chloride 1 Sodium Na explosive 2 Chlorine Cl poison gas This is an example of an emergent property lecture 1 because as the elements are mixed which separately are dangerous they become table salt II Structure and Behavior of Atoms smallest amount of an element a ALL elements are alike b Each atoms has its own kind of atoms c Atoms are made of subatomic particles 1 Proton positive charge weighs 1 Dalton INSIDE nucleus center 2 Neutron no charge weighs 1 Dalton INSIDE nucleus center 3 Electrons negative charge weighs 1 2000 of a Dalton orbits AROUND nucleus 4 Exs H 1 proton 1 electron C 6 protons 6 neutrons 2 electrons d Atomic Numbers number of protons in an atom 1 Important because neutral atoms have the SAME number of protons and electrons 2 Knowing the number of electrons will be important in this course 3 Atomic number is written as a subscript the lower left hand corner e Atomic Mass number of protons number of neutrons 1 Knowing the atomic mass is important in determining concentrations 2 Atomic mass is written as a superscript the upper left hand corner f Isotopes atoms of an element that have a DIFFERENT atomic mass with the SAME atomic number 1 They have a different number of neutrons 2 Radio isotopes isotopes that are unstable that break down and release energy Radioactive isotopes are helpful in biology easily detectable III Electrons and Energy Levels a Electron orbital shells this is where electrons are found orbiting the nucleus and this concept has rules 1 Electrons fill up the closest shell first 1st 2 electrons 2 Outer shells filled in order 2nd and 3rd hold 8 3 If the shell is partially 4 Octet completely Element Valence Hydrogen H 1 Oxygen O 2 Nitrogen N 3 Carbon C 4 atom can t fill all the shells ONLY the outer empty rule all atoms want to fill the outer shell Ex noble elements last column of periodic table have all 8 electrons in the outer shell b Chemical properties of an element depend on the number of electrons in the outermost shell because it determines how well they form IV Chemical Bonds Attractions that hold atoms together a Valence the bonding capacity of an atom number of bonds an atom needs to become stable number of electrons needed to fill the outer shell b Strong Bonds 1 Covalent bond the most common bond in Biol 101 formed by sharing electrons very strong 2 kinds i Nonpolar when atoms have similar or identical electronegativity the ability to attract electrons share electrons ii Polar shares electrons unequally occurs when one atom has a very different electronegativity from the other the ends of the bond are different the one with more electronegativity is negatively charged while the one with less is slightly positively charged generally found in H with O N Cl Ex H2O H positively charged O negatively charged iii Polar and nonpolar molecules are NOT attracted to each other iv Single covalent bonds share 1 pair of electrons v Double covalent bonds share 2 pairs of electrons vi Triple covalent bonds share 3 pairs of electrons Side note electronegativity of common elements Na 0 9 H 2 1 C 2 5 N 3 0 Cl 3 0 O 3 5 very high 2 Ionic bonds formed by electrostatic attraction between two atoms after a COMPLETE transfer of an electron from a donor atom to an acceptor atoms NOT sharing causes a strong charge attraction i Ex NaCl Sodium Chloride Na 1 valence electron Cl 7 valence electrons Sodium loses its electron and becomes Na and Chlorine gains that electron becoming Cl c Weak Bonds some are important to Biol 101 1 Hydrogen Bonds weak charge attraction between a positively charged H atom of a molecule and a negatively charged atom of another atom weak attraction between polar molecules i No electron sharing ii No electron transfer iii Weak bond iv 1 20 strength of a covalent bond v Continually breaking and reforming Ex H2O This model demonstrates the slightly positive charges on both H atoms and the negative charge on the O atom from pulling the 2 valence electrons away from the H atoms Use lowercase delta followed by a or to denote charges in polar molecules Question on first exam what is a Hydrogen bond Draw H2O showing the polar bonds shown above 2 Hydrophobic Bonds nonpolar molecules avoid H2O polar and thus associate with each other afraid of water very little strength in this phenomenon important in membrane structures V Chemical Reactions breaking and forming of bonds a Described by chemical equations that illustrate which atoms are involved how many are involved and which way the reaction goes Ex 3 H 2 N2 2NH3 Side note most biologically important reactions are REVERSIBLE and will eventually reach equilibrium reaction times the same both ways