Chemical Bonding CHEM 101
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This 6 page Class Notes was uploaded by Piper Daniels on Tuesday October 13, 2015. The Class Notes belongs to CHEM 101 at University of Alabama - Tuscaloosa taught by Mrs. Leung in Summer 2015. Since its upload, it has received 15 views. For similar materials see Structural Chemistry, with Application to Chemistry of the Elements in Science at University of Alabama - Tuscaloosa.
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Date Created: 10/13/15
Chapter 6 Chemical Bonding ElectronegativityEN 1 EN the ability an atom has to attract electrons to itself in a chemical bond 2 ENf40 ENH21 Ht E a Higher EN values the more attraction electrons have to the atom 3 Trends a down a group i n increases ii valence electrons are further from the nucleus iii nucleus does not hold onto the bonds as well iv EN decreases down the grouo b across a periodleft to right i Zeff increases ii valence electrons feel a larger positive charge iii valence electrons are held much tighter 4 As you move closer to fluorine most EN vou are increasing EN 5 Must know EN of H B C N O F 8 Cl Br and Dipole 1 Polarity difference in EN between atoms in a bond H E Change in EN ENF ENH 40 21 19 a The larger the change in EN the more polar the bond less equally shared the bonding electrons b The less EN in an atom is demonstrated with 1 the more EN in an atom is demonstrated with n39 2 Dipole moment separation of positive and negative charge a Demonstrated with an arrow underneath pointing towards the more negative side and a cross patch on the side with the less EN Bonds 1 Ionic bonds metal and nonmetal a difference in EN 2 20 2 Covalent bonds nonmetals and nonmetals or nonmetals and metalloids a difference in EN lt 20 Covalent Bonds 1 Nonpolar covalent or nonpolar bonds a difference in EN 3 04 2 Pure covalent bonds a difference in EN O b still classified as a nonpolar bond 3 Polar covalentPolar bond a 04 lt difference in EN lt 20 Lewis Bond Theory 1 Simplest model to show chemical bonds 2 Shows a Dots that represent valence electrons b Connectivity of atoms c Bonding electrons those that are shared between two atoms d Nonbonding electronslone pairs belonging to only one atom 3 Goal achieve a noble gas electron configuration a 8 valence electrons octet b 2 valence electrons for He duet Connectivity 1 H s are terminal must be in the exterior part of the molecule a hydrogen can only form one bond so it cannot be in the middle and form more than one bond 2 More EN atom is exterior a hydrogen is an exception to this 3 If there is H and 0 have the H connected to the O 4 ExCO2 N g Cl D is more EN Ex NH3 ExHNo3 Total Valence Electrons 1 Main group elements Gp A valence electrons 2 Cation subtract electrons number you subtract charge Anion add electrons number you add charge EXAMPLE OF Lewis Structure 1 Connectivity 2 Total Valence Electrons 1 H H Total Vaience e s 2H2x1372es 13 1 in E 5315 Has 3 Distribute the valence electrons a form single bonds first b remaining valence electrons and give them to exterior atoms first lone pairs c then to central atoms as lone pairs 4 Replace bonding electrons with bonds Keep lone pairs a sharing 2 electrons single bond b sharing 4 electrons double bond c sharing 6 electrons triple bond 4 H w n H EXAMPLE 2 N0339 Total valence electna lN 1 it See Sea 3 it es laes llcharge 1 ea 2 Ed ea After all valence electrons have been distributed and an atom is under the octet MOVE NEIGHBORING ATOM S LONE PAIR TO BE BONDING ELECTRONS SHARED 0 Formal Charges 1 Formal charge is the charge the Lewis structure would have if all bonding electrons were shared equally a aka we are ignoring the EN 2 Formal charge Valence electron nonbonding electrons 12 bonding electrons 3 Ex H20 4 H c l H H1122O 0641240 4 Ex No3 left 0 6 6 12 2 1 bottom 0 6 6 12 2 1 right 0 64 12 4 O N 5 12 8 1 Add these together and you get the total charge of nitrate 1 You could have moved the lone pairs from any of the oxygens and it would have worked Purpose of Formal Charges 1 If there are competing Lewis Structures a Connectivity H202 b Which lone pairs to move 2 The M Lewis Structure a more atoms with O formal charges b if formal charges cannot be avoided the best Lewis Structure i formal charges closer to 0 ex 2 vs 1 1 is closer to 0 ii negative formal charges on the more EN atom iii positive formal charges on the less EN atom Thta quot3leth EIEEWUHE h quotIID Elf 1E EHEEVEFDHS nial PRAGTIEE Which s the hat Lewis armature E Ina pairs mm HI 2 Il ha paiira frhm Di quot1 F l ll l HI 1 fham El IN EN d NI d N ESE N1 H 1 th s is the heat h hh the Eharges