CHEM102_FinalPrep_BookNotes - 10.1 Lewis Theory Lewis...

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Unformatted text preview: 10.1 Lewis Theory Lewis Theory was created by G.N. Lewis, Irving Langmuir, and Walther Kossel Valence Shell electrons play an important role in chemical bonding • Electrons are transferred from atom to atom: Ionic Bonding • Electrons are shared between atoms: Covalent Bonding • Electrons are shared to form an Octet • Fundamental ideas of the Lewis Theory : Lewis Symbols : Chemical symbol to represent the nucleus and core electrons of an atom together with dots placed around the symbol to represent valence electrons . 10.2 Covalent Bond Intro Monday, January 03, 2011 8:13 PM Covalent Bonding Sharing of Electrons Coordinate Covalent Bond - a single atom contributes both of the electrons to a shared pair 10.3 Polar Covalent Bonds & Electrostatic Potential Maps Monday, January 03, 2011 8:29 PM Electrons are displaced toward the more nonmetallic element. • The polar charges are represented with ¡ ¢£¤¥¢¦§¨¢©¤¥¨¢©¨¦ª««¬­¢¨«¨©¨®¦¢ª®¯¢ ° for the more nonmetallic. • To make electrostatic potential maps ○ The electron distribution within molecules is approximated by using the Schrödinger Equation. • Polar Covalent Bond - Unequal sharing of electrons Electrostatic potential is the work done in moving a unit of positive charge at a constant speed from one region of the molecule to another. ±² ³ ´ µ¶ ³ · ¸ ±² ¹ ´µ¶ ¹ ·¢º»¼¢±² ³ ½ µ¶ ¹ · ¸ ±² ¹ ½µ¶ ³ · ○ Related to ionization energy (I) and electron affinity (EA) • If Δ EN is very small, the bond is covalent. If it is very large, the bond is ionic. ○ Otherwise it is polar covalent ○ Electronegativity Difference Δ EN is the absolute value of the difference in EN values of bonded atoms • Electronegativity is the an atoms ability to complete for electrons with other atoms to which it is bonded. 10.4 Writing Lewis Structures Monday, January 03, 2011 9:17 PM Show all valence electrons in Lewis Structure • Usually all electrons are paired • Usually each atom requires an outer shell octet of electrons (except for H) • Sometimes multiple covalent bonds (double, triple) form. • Fundamental Requirements Central atom: bonded to two or more atoms • Terminal atom: bonded to one atom • Hydrogen atoms are always terminal atoms ○ Central atoms are generally those with the lowest electronegativity ○ Carbon atoms are always central atoms ○ Molecules and polyatomic ions generally have compact symmetrical structures ○ Rules: • Skeletal Structures 10 Bonding Tuesday, March 01, 2011 12:24 AM Book Notes Page 1 Count lone pair electrons as belonging entirely to the atom on which they are found. ○ Divide bond pair electrons equally between the bonded atoms. ○ FC = number of valence e- in free atom - number lone pair e-- ¡ number bond pair e- ○ Number of valence electrons in the free atom minus the number of valence electrons assigned to that atom....
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This note was uploaded on 02/20/2012 for the course CHEM 102 taught by Professor Spears during the Fall '08 term at Northwestern.

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CHEM102_FinalPrep_BookNotes - 10.1 Lewis Theory Lewis...

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