有机化学英语课件.pptVIP

Chapter 1 – Covalent Bonding and Shapes of Molecules Write the electron configuration corresponding to a neutral atom or to an ion derived from it when given the atomic number of any element between hydrogen and argon in the periodic table. Describe the difference between ionic and covalent bonding. State the octet rule and discuss its significance. Determine the direction of polarization of a covalent bond on the basis of the difference in electronegativity of the atoms that it connects. Calculate the formal charges on atoms in Lewis structures. Write the structures of organic molecules using condensed structural and bond-line formulas. Write Lewis structures for constitutionally isomeric substances. Electronic structure of atoms Electrons in an atom are confined in principal energy levels called shells. Electron shells are identified by the numbers 1, 2, 3, and so on. Each shell can contain up to 2n2 electrons. Shells are divided into subshells designated by the letters s, p, d, and f. Electrons are grouped in orbitals which can hold two electrons. Orbitals are listed below: 1s, 2s, 2p (2px, 2py, 2pz), 3s, 3p, 3d, etc. Rules for determining the ground-state electron configuration of an atom Orbitals fill in order of increasing energy from lowest to highest. Each orbital can hold up to two electrons. When orbitals of equivalent energy are available but there are not enough electrons to fill them completely, then one electron is added to each equivalent orbital before a second electron is added to any one of them. Lewis Structure Valence electrons: Electrons in the valence (outermost) shell of an atom. Valence shell: The outermost electron shell of an atom. Lewis structure: The symbol of an element surrounded by a number of electrons in the valence shell of the atom. Guidelines for Drawing Lewis structures of Molecules and Ions Determine the number of valence electrons in the molecule or ion. Determine the arrangement of atoms in the atoms in the