Orgo Notes - Chapter 1 Introduction to Structure and...

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Chapter 1 : Introduction to Structure and Bonding in Organic Compounds Compounds are divided broadly into two bonding models, ionic and covalent. Ionic compounds are composed of ions, structural units that may be single atoms or groups of atoms bearing positive charges. Usually crystalline solids with high melting points. Many of these compounds dissolve in water to form solutions that conduct electricity. In covalent compounds, the structural units are molecules having no net charge. May be gases, liquids or solids. Nonpolar covalent compounds do not dissolve in water to any great extent. Polar covalent compounds ionize only slightly in aqueous solutions. The forces that act between charged particles are called electrostatic forces. Ions arranged alternately in a three-dimensional array usually make a crystal lattice. Ionic bonding consists of electrostatic attractions between ions of opposite charge. The individual ion is a sphere bearing a symmetrical direction of charge. For this reason, there is no particular direction to bonding in ionic compounds. Melting and boiling points are an indication of the strength of the electrostatic forces holding ions together. The covalent bond is represented as the sharing of a pair of electrons between two atoms. Stable molecules or ions, with a few exceptions, have eight electrons in the outermost shell, the valence shell, of each atom. This stable configuration of electrons is called an octet. An atom having a filled valence shell is said to have a closed shell configuration. The Lewis structure of a covalent molecule shows all the electrons in the valence shell of each atom; the bonds between atoms are shown as shared pairs of electrons. The shared electrons are called bonding electrons. Charges as well as numbers of atoms must always be balanced in writing equations. Connectivity: the structure of the molecule is described in terms of the atoms that are connected to each other by means of covalent bonds. The connectivity in a molecule is determined by looking at the structure and describing which atom is bonded to which others. Hydrocarbons: compounds containing only carbon and hydrogen. Saturated hydrocarbons: compounds containing just carbon atoms and all the hydrogen atoms they can hold.
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Isomers: compounds with the same molecular formula but different structural formulas. A molecular formula doesn’t give any information about connectivity but tells us whether the structural formula for the compound can contain rings or atoms bonded to each other by more than one bond. If the formula has 2n +2 hydrogen atoms for every n carbon atoms, the structure will not have any rings or more than one bond between the same two atoms in it. Carbon atoms are also found bonded to atoms other than hydrogen, like oxygen, the
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This note was uploaded on 11/29/2010 for the course CHEM 34555 taught by Professor Koraeda during the Spring '10 term at Michigan Flint.

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Orgo Notes - Chapter 1 Introduction to Structure and...

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