LIFE 102 1st edition Lecture 2Outline of Last Lecture (CH. 1) I. Biology: the study of life II. Uniformity and DiversityOutline of Current Lecture (CH. 2) I. Elemental MatterII. Atomic StructureIII. Chemical BondsIV. Chemical ReactionsCurrent LectureCHAPTER 2: CHEMICAL CONTEXT OF LIFEElemental MatterI. Element: substance that cannot be broken down by a chemical reactionII. Compound: two or more elements combined in a fixed ratioIII. There are 25 elements essential for lifeA. 96% of living matter is made up of the bulk elements Hydrogen, Oxygen, Nitrogen, and Carbon (Remember HONC)B. Trace elements are still essential for life, but only needed in minute quantities [Examples: Boron (B), Iodine (I), Iron (Fe)]Atomic StructureI. Atom: the smallest unit of an elementA. Consist of Protons (+), Electrons (-) and neutrons (0)*neutral*Atoms are mostly empty space: if an atom is a football stadium, the nucleus is a pencil eraser, and the electrons are gnats.II. Atomic Number: Number of protons in the nucleusA. Example: Helium (2He) has two protonsB. IF YOU CHANGE THE NUMBER OF PROTONS YOU CHANGE THE ELEMENT III. Mass Number: # of protons + # of neutronsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.A. Example: Helium 2He has a mass number of 4 because 2 Protons + 2 Neutrons= 4B. Standard atoms have the same number of neutrons as protons, but modified atoms can undergo changes that make them unequalIV. Modified atomsA. When atoms gain or lose an electron it becomes a positively or negativelycharged atom called an ionB. If it loses or gains a neutron it becomes an Isotope: the same element but with a different massExample: 12C 13C 14C They have different atomic mass, but all Carbon atoms have 6 protonsV. Electrons are arranged in Electron ShellsA. Shells are found at different distances to the nucleus and can hold a maximum # of electronsExample: Shell 1 can hold 2 electrons; shell 2 can hold 8 electronsB. Valence Shell: Outermost shell that contains electronsC. Atoms want to make their valence shell complete because it is the most energetically stableExample: Nobles Gases (such as Helium, Neon and Argon) have full valence shells and are inert: they do not react readilyChemical BondsI. Two strategies for atoms to fill their valence shells:A. Ionic BondsB. Covalent BondsII. Ionic bonds: donate or accept electron from another atomA. Now, both atoms have a full outer shellB. Sodium is now a Cation (a positively charged atom) because it lost an electronC. Chloride is now an Anion (a negatively charged atom) because it gained an electronD. Cations and Anions attract each otherE. Ionic bonds form salt crystals, such as the table salt (NaCl) in the diagram above, because the molecules stack themselves like blocks, positive end to negative and so on.III. Covalent Bonds: Two atoms can SHARE an electron pair, that electron can count to fill both of the atoms outer shells.A. The number of electrons in the valence shell determines how many bonds that atom can make 1bond 2 bonds 3bonds 4bonds 3bonds 2bonds 1bond 0 bondsB. Polar Covalent Bonds: the electrons are not shared equally between the two atoms  creates a polar compoundC. Hydrogen bonds (which are weak and temporary) can form between two polar molecules because some regions of the molecule are more positive or negative than the other. (This will be discussed more next chapter)Chemical ReactionsI. Molecules react and create bonds with each other, which yields a whole new product!A. A+B  C+DII. Mass Conservation Law: all atoms present in the reactants are present in the productsA. Example: C6H12O6 + 6 O2  6 CO2 + 6 H2OB. Mass cannot be created or destroyed III. Chemical reactions are REVERSIBLEA. Example: A + B IV. Chemical Equilibrium: when the rate of forward reaction is equal to the rate of reverse reaction.A. Reactions are still taking place, it’s just that there is no change in the concentrations of reactions and productsC