Organic Chemistry 4 th Edition Paula Yurkanis Bruice Chapter 1 Electronic Structure and Bonding Acids and Bases Irene Lee Case Western Reserve University Cleveland, OH ©2004, Prentice Hall • Organic compounds are compounds containing carbon • Carbon neither readily gives up nor readily accepts electrons • Carbon shares electrons with other carbon atoms as well as with several different kinds of atoms Organic Chemistry The Structure of an Atom • An atom consists of electrons, positively charged protons, and neutral neutrons • Electrons form chemical bonds • 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 • Quantum mechanics uses the mathematical equation of wave motions to characterize the motion of an electron around a nucleus • Wave functions or orbitals tell us the energy of the electron and the volume of space around the nucleus where an electron is most likely to be found • The atomic orbital closer to the nucleus has the lowest energy • Degenerate orbitals have the same energy Table 1.1 • The Aufbau principle: electrons occupy the orbitals with the lowest energy first • The Pauli exclusion principle: only two electrons can occupy one atomic orbital and the two electrons have opposite spin • Hund’s rule: electrons will occupy empty degenerated orbitals before pairing up in the same orbital • Ionic compounds are formed when an electropositive element transfers electron(s) to an electronegative element Covalent Compounds • Equal sharing of electrons: nonpolar covalent bond (e.g., H 2 ) • Sharing of electrons between atoms of different electronegativities: polar covalent bond (e.g., HF) Electrostatic Potential Maps