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Course Outline • What is Organic Chemistry? Organic chemistry is the chemistry of compounds that contain the element of carbon. Organic chemistry affect every facet of our lives, and therefore it is important and useful to know something about them. C Course IInstructor: t t D Y Dr. Yuming i Zh Zhao Teaching Assistant: TBA Lectures: Mon, Wed, Fri 11:00-11:50 Room: SN 2019 Text: Organic Chemistry, 6th Ed, by Paula Bruice Marking Scheme Lab Two Quizzes Final exam 20% 5% of the lower mark + 25% of the higher mark 50% • What makes Carbon So Special? p (1) Carbon is in the middle, so it neither give or accept electrons readily (2) Carbon shares electrons with other atoms (including carbon) (3) Carbon C b can fform millions illi off compounds d with ith a wide id range of chemical properties Welcome to the World of Organic g Chemistry! y Methotrexate, Anticancer Drug AZT HIV Drug AZT, Tamiflu Influenza Drug 5-Fluorouracil Colon Cancer Drug g Prozac A tid Antidepressant t Chapter p 1 Electronic Structure and Bonding Acids and Bases The Structure of an Atom nucleus + proton neutron t + + + + + electron cloud l d In a neutral atom, the number of protons in the nucleus equals th number the b off electrons. l t • The size si e of atom is defined b by the space taken by the electrons • The mass of the electron is quite small compared to the mass of proton and neutron, so can be ignored for all practical purposes Particle Charge (a.u.) Mass (a.u.) Proton Neutron +1 0 ~1 ~1 1 Electron -1 1/2000 4A Group number 6 Atomic number C Element symbol Element name Atomic weight Carbon 12.011 • Atomic number: numbers of protons in its nucleus • Mass number: the sum of the protons and neutrons of an atom • Isotopes have the same atomic number but different mass numbers • The atomic weight: the average weighted mass of its atoms • Molecular weight: the sum of the atomic weights of all the atoms in the molecule The Distribution of Electrons in an Atom Electrons are added to particular shells of orbitals p around the nucleus. e Electrons are first added to the shell closet to the nucleus e e The modern electron shell model of the atom was first developed by Niels Bohr in the early 1920s. Each shell contains a certain number of subshells called orbitals. An orbital is a region of space that is high in electron density. density • Electron configuration g is a description p of where electron reside in atoms and molecules. • Three rules determine how electrons occupy orbitals Rule R l #1 1: Th There mustt b be 0 0, 1 1, or 2 electrons l t iin an orbital bit l (Pauli exclusion principle) Rule # 2: Fill the lowest energy orbital first (aufbau principle) Rule # 3: Do not pair the electrons unless forced to (Hund’s rule) Electron configuration g of carbon: 1s22s22p p2 3d 3p 3s 2p 2s 1s V l Valence electrons l t Core electrons Bonding g • Bonding is the joining of two atoms in a stable arrangement. • Through Th h bonding, b di atoms t attain tt i a complete l t outer t shell h ll off valence electrons. • Through bonding, atoms attain a stable noble gas configuration of electrons electrons. Lewis’s theory: y an atom will g give up, p, accept, p , or share electrons in order to achieve a filled outer shell or an outer shell that contains eight electrons. Ionic Bonds Are Formed by the Transfer of Electrons Attractive forces between opposite pp charges g are called electrostatic attractions 15 Covalent Bonds Are Formed by Sharing Electrons 16 • Equal sharing of electrons: nonpolar covalent bond (e.g., H2) • Sharing of electrons between atoms of different electronegativities: polar covalent bond (e (e.g., g HF) 17 A polar covalent bond has a slight positive charge on one end d and d a slight li ht negative ti charge h on th the other th 18 A Polar Bond Has a Dipole Moment • A polar bond has a negative end and a positive end di l momentt (D) = μ = e x d dipole e: magnitude of the charge on the atom d: distance between the two charges 19 Lewis Structure Lewis structures are electron dots representations for molecules molecules. 1. Draw a o only y tthe e valence a e ce e electron ect o 2. Give every second-row element no more than eight electrons 3. Give each hydrogen two electrons Formal charge = number of valence electrons – (number of lone pair electrons +1/2 number of bonding electrons) 20 Nitrogen has five valence electrons Carbon has four valence electrons Hydrogen y g has one valence electron and halogen g has seven 21 How to Construct a Reasonable Lewis Structure? 1. Count the total number of valence electrons a. B = 3, C= 4, N = 5, O = 6, F = 7 b. If the total charge is -1, -2, or -3, ADD 1, 2, or 3 valence electron respectively c. If the total charge is +1, +2, or +3, SUBTRACT 1, 2, or 3 valence electron respectively 2. 3. 4. Write the Skeleton of the molecule Subtract two electrons for each single g valence bond Distribute the remaining electrons as lone pairs around the atoms a. Start from the outside atoms and work inward b. Attempt to achieve octet/duet on each atom 5. If an atom is deficient of its octet/duet, convert lone pairs from neighboring atoms into bonding pairs, thereby creating double and/or triple bonds Draw the Lewis Structure for NO2• Total number of valence electrons = 5(N) + 6(O) × 2 + 1 (-eV) = 18 • Draw the molecular skeleton • Distribute Di t ib t th the reaming i electrons l t (18 – 4 = 14) •Convert one electron lone pair of oxygen into a covalent bond to fulfill octet on nitrogen Important Bond Numbers Neutral Cationic Anionic 24 Kekulé Kekul é Structures Condensed Structures CH3Br CH3OCH3 HCO2H CH3NH2 N2 Drawing of Carbon Skeleton in the Zigzag format The end of every line represents a carbon atom