ERM Ch. 1 Sorrell Part1 Su2019.ppt

ERM Ch. 1 Sorrell Part1 Su2019.ppt - Chapter 1 Structure of...

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Chapter 1 Structure of Organic Molecules and Organic Nomenclature Organic Chemistry: Chemistry of substances containing carbon
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2 Gilbert N. Lewis Valence shell: Valence shell: the outermost electron shell of an atom Valence electrons: Valence electrons: electrons in the valence shell of an atom; these electrons are used to form chemical bonds Lewis structure: Lewis structure: the symbol of the atom represents the nucleus and all inner shell electrons dots represent valence electrons Lewis Structures Lewis Structures Table 1.4 Lewis Structures for Elements 1-18 Chapter 1
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3 Chemical Bonds: The Octet Rule Octet Rule Atoms form bonds to produce the electron configuration of a noble gas (because the electronic configuration of noble gases is particularly stable) For most atoms of interest this means achieving a valence shell configuration of 8 electrons corresponding to that of the nearest noble gas Atoms close to helium achieve a valence shell configuration of 2 electrons Atoms can form either ionic or covalent bonds to satisfy the octet rule Chapter 1
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4 Electronegativity Electronegativity is the ability of an atom to attract electrons It increases from left to right and from bottom to top in the periodic table (noble gases excluded) Equal sharing of electrons: nonpolar covalent bond (H 2 ) Sharing of electrons between atoms of different electronegativities: polar covalent bond (HF) Chapter 1
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5 Ionic Bonds When ionic bonds are formed atoms gain or lose electrons to achieve the electronic configuration of the nearest noble gas an atom that gains electrons becomes an anion an atom that loses electrons becomes a cation The resulting oppositely charged ions attract and form ionic bonds This generally happens between atoms of widely different electronegativities (greater than 1.9) Example Lithium loses an electron (to have the configuration of helium) and becomes positively charged Fluoride gains an electron (to have the configuration of neon) and becomes negatively charged The positively charged lithium and the negatively charged fluoride form a strong ionic bond (actually in a crystalline lattice) Chapter 1
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6 Covalent Bonds Covalent bonds occur between atoms of similar electronegativity (close to each other in the periodic table) Atoms achieve octets by sharing of valence electrons Molecules result from this covalent bonding Valence electrons can be indicated by dots (electron-dot formula or Lewis structures) but this is time-consuming The usual way to indicate the two electrons in a bond is to use a line (one line = two electrons) Chapter 1
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7 The carbon atom is unique in its bonding in that it can form stable molecules consisting of chains of carbon atoms of any length Carbon atoms can also form four bonds to other atoms which this leads to incomprehensibly large numbers of possible molecules Carbon forms strong covalent bonds to other carbons and to other elements such as hydrogen, oxygen, nitrogen and sulfur Carbon is Unique in its Chemical Bonding Chapter 1
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