lecture 3 - Lecture 3 Organic Chemistry I Prof. Jonathan L....

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Organic Chemistry I 310/318M Pre-Health Professionals Unique numbers: 54410, 54435, 54440, 54445, and 54655 Prof. Jonathan L. Sessler Lecture 3
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Simplified View of Bonding • Coulomb’s law of electric charge: – Opposite charges attract each other – Like charges repel each other • Bonds are made by simultaneous coulombic attraction and electron exchange Bond strength : Energy released as atoms are brought together, until charge repulsion takes over. Bond length : Distance between two nuclei.
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G. N. Lewis’ Model of Bonding • Atoms interact in such a way that each participating atom acquires an electron configuration that is the same as that of the noble gas nearest it in atomic number. – An atom that gains electrons becomes an anion anion . – An atom that loses electrons becomes a cation cation . – The attraction of anions and cations leads to the formation of ionic solids ionic solids . . This ionic interaction is often referred to as This ionic interaction is often referred to as an an ionic bond ionic bond . – An atom may share electrons with one or more atoms to complete its valence shell; a chemical bond formed by sharing electrons is called a covalent bond covalent bond . Bonds may be partially ionic or partially covalent; these bonds are called polar covalent bonds polar covalent bonds
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Lewis Dot Structures for Atoms • Gilbert N. Lewis Valence shell: Valence shell: – The outermost occupied 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 and in chemical reactions. Lewis dot structure: Lewis dot structure: – The symbol of an element represents the nucleus and all inner shell electrons. – Dots represent electrons in the valence shell of the atom.
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Lewis Dot Structures for Atoms
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• A rough guideline: – Ions will form if the difference in electronegativity between interacting atoms is 1.9 or greater. – Example: sodium (EN 0.9) and fluorine (EN 4.0) – We use a single-headed (barbed) curved arrow to show the transfer of one electron from Na to F. – In forming Na + F - , the single 3 s electron from Na is transferred to the partially filled valence shell of F. Formation of Ions +F - (1 s 2 2 s 2 2 p 6 ) Na + (1 s 2 2 s 2 2 p 6 ) F(1 s 2 2 s 2 2 p 5 ) + Na(1 s 2 2 s 2 2 p 6 3 s 1 )
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Ionic and Covalent Bonds: Ionization Potential vs. Electron Affinity M M + + e - ∆ Η ο = IP ( ionization potential ) Li Li -e - (like He) 123.6 kcal/mole Na Na - (like He) 118.0 kcal/mole extra electron, valence e - X X - - ∆ Η ο = EA ( electron affinity) e - Cl Cl e - 83.3 kcal/mole
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lecture 3 - Lecture 3 Organic Chemistry I Prof. Jonathan L....

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