Biol 1107 Chapter 2I. Metabolism – sum of the chemical reactions that allow lifeA. Chemical properties of molecules determine how they act1. We need to know something of chemistry to understand biologyB. All matter is made of elements1. Represented by a unique chemical symbola. Usually 1st or 1st and 2nd letters of the namei. Ex, O or Nib. Sometimes use letters from Latin namei. Ex, Fe2. 92 naturally occurring elementsa. Four elements make up 96+% of organismsi. O, N, C, Hb. Trace elements are essential for lifei. Needed in very small amountsii. Most of minerals in vitamins are trace elementsc. Quantity elements – needed in intermediate amountsi. Ca, Na, K, etc.3. Elements are not changed by chemical reactionsa. Ex, 2H + O  H2OC. Elements are made of atoms1. Smallest portion of an element that retains all the properties of the elementa. 1 atom of C behaves exactly the same as a ton of Ci. Has all the same chemical and physical propertiesb. Atoms have subcomponentsi. Protons – positively charged particles in nucleusii. Neutrons – uncharged particles found in nucleusiii. Electrons – negatively charged particles around nucleus2. Number of protons determines what element it isa. Called the atomic numberi. The periodic table is arranged by atomic numberb. Every atom of the same element has same atomic numberc. Ex, every atom with exactly 1 proton is Hd. Ex, every element with exactly 8 protons is O3. Atomic mass is number of protons + neutronsa. Ex, if an O atom has 8 protons and 8 neutrons, its atomic mass is 16b. Ex 2, a chlorine atom has 17 protons and 18 neutronsi. What is its atomic number?ii. What is its atomic mass?c. Different atoms of same element may have different atomic massesi. Same number of protons, different number of neutronsii. Called isotopes- Ex, C-12 and C-13- Each has 6 protons and either 6 or 7 neutronsiii. Some isotopes are unstable = radioisotopes- Breakdown over time- Release radiation- Useful in many ways (medicine, science, household, etc)D. Electrons – orbit around the nucleus1. Found in layers called orbitals or shellsa. Different orbitals have different energy levelsi. Furthest from the nucleus is the valence shellii. Valence shell has the highest energyb. Shells generally fill from inner to outeri. ie, outer shells don’t start forming until inner shells are full 2. Electrons in valence shell are valence electrons *a. These have highest energyb. First electrons involved in chemical reactions i. Determines chemical properties of the atom3. Atoms are at lowest energy (= most stable) when valence shell is fulla. For H and He, valence shell is full with 2e-b. For all other elements, valence shell is full when it has 8e-4. Atoms ‘strive’ to achieve lowest energy statea. Can do this in three waysi. Can acquire more e- to fill valence shell- Usually elements with mostly full shellsii. Can give away e- to empty out valence shell- Usually elements with mostly empty shellsiii. Can share e- with other atomsII. Chemical reactions – two or more chemicals interact to form new products A. May result in molecules and/or compounds1. Molecule – 2 or more atoms strongly combined into a stable particlea. May be homogeneous (ex, O2)b. May be heterogeneous (ex, CO2)2. Compounds – always heterogeneous (ex, NaCl)a. May be stable or unstableB. Chemical formulas describe substances1. A molecular formula shows the number and ratio of atomsa. Ex, H2O2. A structural formula shows the arrangement of atomsa. Ex, H—O—H b. Obviously this contains more informationC. Chemical equations describe chemical reactions1. Reactants – beginning chemicalsa. Listed on left2. Products – newly created substancesa. Listed on righti. Ex. C6H12O6 + 6O2  6CO2 + 6H2O + energy3. Some reactions are reversiblea. Have a double arrowb. Length of arrow shows which direction is favoredi. Ex, CO2 + H2O  H2CO3 (draw in other arrow)D. Redox reactions – special type of reaction1. Electron is transferred from one molecule to anothera. When e- is transferred, energy is transferred2. Redox stands for reduction-oxidationa. Composed of two half reactions that occur simultaneouslyb. Reduction – reaction where substance gains 1+ electronsi. Results in a reduction of its chargec. Oxidation – reaction where substance loses 1+ electronsd. Leo Ger – pneumonic device 3. Redox reactions are central to photosynthesis and cellular respirationIII. Atoms may be joined by chemical bonds – several typesA. Covalent bonds – strongest type1. Electrons in the valence shell are shared between atomsa. Results in a more filled shell for each2. Can be represented by Lewis structuresa. O + O  O O (draw in lines)b. Can be single, double, or triple covalent bondsi. 1, 2, or 3 pairs of e- sharedii. Ex, ethane, ethene, ethyne (acetylene)3. Covalent bonds may be polar or nonpolara. Polar bonds have unequal sharing of electronsi. Electronegativity is a measure of how strongly an element pulls electrons towards itii. If 2 atoms have differing electronegativities, a bond between them will be polariii. Since e- spends more time around one atom, results in partial charges- Ex, H2Ob. Nonpolar bonds have equal sharing of electronsi. Occurs when atoms have same or very similar electronegativitiesii. Bonds in homogeneous molecules will be nonpolariii. Ex, O2B. Ionic bonds are bonds between ions (charged atoms)1. Cations are positively charged atoms2. Anions are negatively charged atomsa. Have the –ide suffix3. Ionic bonds results when charges on cation and anion attract each othera. Ex, NaCl is a compound containing an ionic bond between Na+ and Cl-4. Ionic bonds are weaker than covalent bondsa. Usually dissociate in waterC. Hydrogen bonds – weak attractions involving partially charged H1. A partial positive charge exists on a H in a polar covalent bonda. Because the e- spends less time around it2. The partial positive can attract a negative charge in different molecule3. Draw interactions in H2O and in H2O + NaCl4. Individually very weaka. Very strong when many are presentIV. Water is essential for lifeA. Can live much longer without food than waterB. Bulk of most organisms is water (60-70% of human mass is water)C. Most of our metabolic reactions occur in water1. Polar and ionic substances dissolve easily in watera. Called hydrophilicb. Ex, sugars, salts, etc.2. Nonpolar substances generally don’t dissolve well in watera. Called hydrophobicb. Ex, oilsD. Water forms hydrogen bonds1.