Chapter_1_notes

Chapter_1_notes - Chem 2261 Course Notes Bonding Structure/Acids Bases(see Bruice Chapter 1 Bonding and Structure Valence Electrons Are Determined

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Chem 2261 Course Notes Bonding & Structure/Acids & Bases (see Bruice, Chapter 1) 1 Bonding and Structure Valence Electrons Are Determined by Position in the Periodic Table The periodic table can be divided into 4 blocks according to the type of orbital (s, p, d or f) being filled as we cross the block from left to right. s d p f insert these here 3B 2B 4 blocks of elements 1A 2A 3A 4A 5A 6A 7A 8A In organic chemistry we will focus on compounds of the s and p block elements: In order to be effective at what comes next (drawing Lewis structures) you should know, without consulting a periodic table (or even having to think about it) where H, C, N, and O lie on the periodic table. If you need to, make an effort to memorize the positions of these four elements now. The position tells how many valence electrons an element possesses, which, in turn, tells you how many bonds are needed to produce a stable compound of the element (8 - # of valence electrons, except for H which only makes one bond). Based on their positions in the periodic table, we can see than C needs 4 more electrons, N needs 3 more electrons, and O needs 2 more electrons. Next you should memorize the position of other common atoms in organic structures such as: B (to the left of C) Group 3A needs 5 more electrons F (to the right of O) Group 7A needs 1 more electron P and S (below N and O) Same requirements as N and O (Groups 5A and 6A) Cl, Br, and I (below F) Group 7A needs 1 more electron (like F) Al and Si (below B and C) Same requirements as B and C (Groups 3A and 4A) Li, Na and K (below H) Give up one electron to form ionic compounds (w. Li + , Na + , K + ) Mg (to the right of Na) Gives up two electrons to form an ionic compound (w. Mg +2 ) H Li Na K Be Mg Ca Sr Ba B Al C Si N P O S F Cl Ne Ar Br I He 1A 2A 3A 4A 5A 6A 7A 8A
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Chem 2261 Course Notes Bonding & Structure/Acids & Bases (see Bruice, Chapter 1) 2 Ionic, Covalent and Polar Bonds Simple compounds of metals with nonmetals are held together by ionic bonds which result from the attraction of oppositely charged ions. For example: + + ionic bond NaF salt + 1s 2 2s 2 2p 6 1s 2 2s 2 2p 6 same as 1s 2 2s 2 2p 6 filled octet F Na Na F Na F Ne In ionic compounds, all valence electrons from the metal are transferred to the nonmetal so that the metal is fully oxidized while the nonmetal is fully reduced (this is the general case; there are exceptions which need not concern us right now). The result is that both atoms attain a closed-shell configuration or filled octet. In the example above, both ions (Na + and F ) of the salt NaF have the same electronic configuration as the inert element Ne. Organic compounds comprising the elements H, C, N, and O (as well as other elements) are generally held to together by covalent bonds where electron pairs are shared between atoms. For example: +4 +3 +2 4 covalent bonds 3 covalent bonds 2 covalent bonds + multiple bonding double bonds triple bond C H H H H = N H H H = O H H OC O = = NN = CH C H H H H NH N H H H OH O H H CO C OO N N
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This note was uploaded on 04/21/2008 for the course CHEM 2261 taught by Professor Crowe during the Fall '08 term at LSU.

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Chapter_1_notes - Chem 2261 Course Notes Bonding Structure/Acids Bases(see Bruice Chapter 1 Bonding and Structure Valence Electrons Are Determined

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