【正文】 the intervention of an outside vital force.（4）In 1828 when Friedrich W246。hler produced ureaa pound known to be excreted by mammals by heating ammonium cyanate, an inorganic mineral. For the first time, an “organic” pound had been obtained from something other than a living organism and certainly without the aid of any kind of vital force. Clearly，chemists needed a new definition for “organic pounds.” The importance of Organic Chemistry What is Organic Chemistry?Organic chemistry is the study of carbon pounds. Thus Organic pounds are now defined as pounds that contain carbon.What makes carbon so special? Why are there so many carboncontaining pounds? The answer lies in carbon’s position in the periodic table. Carbon is in the center of the second row of elements. The atoms to the left of carbon have a tendency to give up electrons, whereas the atoms to the right have a tendency to accept electrons.Because carbon is in the middle, it neither readily gives up nor readily accepts electrons. Instead, it shares electrons. Carbon can share electrons with several different kinds of atoms, and it can also share electrons with other carbon atoms. Consequently, carbon is able to form millions of stable pounds with a wide range of chemical properties simply by sharing electrons. The distribution of Organic pounds:(1)All of the molecules that make life possible—proteins, enzymes, vitamins, lipids, carbohydrates, and nucleic acids—contain carbon, so the chemical reactions that take place in living systems, including our own bodies, are organic reactions.(2)Most of the pounds found in nature—those we rely on for food, medicine, clothing (cotton, wool, silk), and energy (natural gas, petroleum)—are organic as well.(3)Important organic pounds are not, however, limited to the ones we find in nature. Chemists have learned to synthesize millions of organic pounds never found in nature, including synthetic fabrics, plastics, synthetic rubber, medicines, and even things like photographic film and Super glue. Many of these synthetic pounds prevent shortages of naturally occurring products. How to study Organic ChemistryOrganic chemistry is a study of the relationship between the structure of molecules and their reaction.If you expect to learn organic chemistry well, you must draw and redraw the structures of pounds and write out equations as you are studying.To study effectively, you should read the assignments before attending lectures. Spend most of you study time working out the problems. Work all of the problems, no matter how simple they seem, in writing and in full detail.In addition, the study guide contains concept maps, which are summaries of important ideas presented in outline form. Covalent Bonding amp。 Shapes of Molecules Schematic View of an AtomA small dense nucleus, diameter 1014 ~1015m, which contains positively charged protons and most of the mass of the atom.An extranuclear space, diameter 1010 m, which contains negatively charged electrons. Electron Configuration of AtomsElectrons are confined to regions of space called principle energy levels (shells) . Each shell can hold 2n2 electrons (n = 1,2,3,4......) Electron Configuration of AtomsShells are divided into subshells called orbitals, which are designated by the letters s, p, d, f,........s (one per shell) p (set of three per shell 2 and higher) d (set of five per shell 3 and higher) .....Aufbau Principle: Orbitals fill in order of increasing energy from lowest energy to highest energy.Pauli Exclusion Principle: Only two electrons can occupy an orbital and their spins must be paired.Hund’s Rule: When orbitals of equal energy are available but there are not enough electrons to fill all of them, one electron is added to each orbital before a second electron is added to any one of them. Lewis Dot StructuresGilbert N. LewisValence shell: the outermost occupied electron shell of an atomValence electrons: electrons in the valence shell of an atom。 these electrons are used to form chemical bonds and in chemical reactionsLewis dot structure: the symbol of an element represents the nucleus and all inner shell electronsdots represent valence electronsLewis Dot Structures for Elements 118 Lewis Model of BondingAtoms bond together so that each atom acquires an electron configuration the same as that of the noble gas nearest it in atomic numberan atom that gains electrons bees an anionan atom that loses electrons bees a cationthe attraction of anions and cations leads to the formation of ionic solidsan atom may share electrons with one or more atoms to plete its valence shell。 a chemical bond formed by sharing electrons is called a covalent bondbonds may be partially ionic or partially covalent。 these bonds are called polar covalent bonds Formation of IonsA rough guideline: ions will form if the difference in electronegativity between interacting atoms is or greaterexample: sodium (EN ) and fluorine (EN )we use a singleheaded (barbed) curved arrow to show the transfer of one electron from Na to Fin forming Na+F, the single 3s electron from Na is transferred to the partially filled valence shell of F Polar and Nonpolar MoleculesTo determine if a molecule is polar, we need to determine if the molecule has polar bondsthe arrangement of these bonds in spaceMolecular dipole moment (m): the vector sum of the individual bond dipole moments in a moleculereported in debyes (D)these molecules have polar bonds, but each has a zero dipole momentthese molecules have polar bonds and are polar moleculesformaldehyde has polar bonds and is a polar molecule ResonanceFor many molecules and ions, no single Lewis structure provides a truly accurate representationLinus Pauling 1930smany molecules and ions are best described by writing two or more Lewis structuresin