Chem1212K, Week 2 Notes
Chem1212K, Week 2 Notes CHEM 1212K
Popular in Principles Chemistry II w/Lab
verified elite notetaker
Popular in Chemistry
1151K - B01
verified elite notetaker
This 3 page Class Notes was uploaded by Bethany B. on Sunday August 28, 2016. The Class Notes belongs to CHEM 1212K at Georgia Gwinnett College taught by Omar Villanueva in Fall 2016. Since its upload, it has received 3 views. For similar materials see Principles Chemistry II w/Lab in Chemistry at Georgia Gwinnett College.
Reviews for Chem1212K, Week 2 Notes
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 08/28/16
8.28.16 Chemistry 1212K[Week 2] Chapter9 Lecture Cont. BondStrength Lengths of covalentbonds determine the type of bondand their strength o Triple bond (short;strong)< Double bond < Single Bond(long; weak) Polar CovalentBonds Polar covalentbondis a covalentbondwithgreaterelectrondensity around one of the two atoms o HF (extremely strongacid); Fluorine has sevenelectrons andhydrogen only has one,so the polarity goes towards fluorine o Anythingthat’s electronrichis slightly negative,anythingthatis electron poor is slightly positive o Whenthe polarity cancels outthe whole molecule is nonpolar. Electronegativity—onthe periodic table,electronegativity generally increases across aperiodand decreases downagroup o Mostelectronegativeelementis fluorine,leastelectronegativeis francium. DIFFERENCE BOND TYPE Nonpolar Covalent 0 2 Ionic 0< AND <2 Polar Covalent Steps for Writingthe Lewis Structures 1. Sum the valenceelectronsfromall the atoms. 2. Use apair of electrons to formabond betweeneachpair of boundatoms. 3. Atoms usually have noble gas configurations.Arrange the remainingelectrons to satisfy the octetrule (or duet rule for hydrogen). OctetRule—elements formstable molecules whensurroundedby eightelectrons. DuetRule—hydrogenforms stable molecules whereitshares twoelectrons. Review C, N, O, and F always obey the octetrule B, Al,and Be oftenhave no more thansix electrons Second-row elements never exceedthe octetrule Third-rule and heavier elements oftensatisfy the octetrule but canexceedthe octetrule by using their empty valence dorbitals. The leastelectronegative atomgoes inthe middle (withthe exceptionof Hydrogen)whenwriting the chemical structure 3- Lewis-dotstructurepractice:HCN,XeF ,PO 4 4 Formal Charges Usedto determine the “best”lewis dotstructure Negative charges shouldendupon most electronegative atoms Try to minimize formal charges to zero FC= [number of val.e on FREEatom]—[number of “Dots”]—[number of “Lines”] o Assume: lone pair electrons belongentirely to the atomin question,only look at the specific atom,and sharedelectronsare dividedequally betweenthe two sharingatoms. The sum of the formal charges of all atoms in a givenmolecule or ionmustequal the overall charge onthatspecies. Resonance Structures Representations of differentways to draw a“best”lewis dotstructure Actual structure is anaverage of the resonance structures. Electrons are really delocalized—they canmovearoundthe entire molecule. If youchange the formal charges,thenit is nota resonance structure Chapter10 Lecture VSEPRModel:Valence Shell Electron-PairRepulsion The structure aroundagivenatomis determined principally by minimizing electronpair repulsions.(They wantto spreadoutas much as they can.) Steps to Apply the VSEPR Model 1. Draw the Lewisstructure forthe molecule 2. Countthe electronpairs andarrange themin the way thatminimizes repulsion (put the pairs as far apartas possible) 3. Determine the positions of the atoms fromthe way electronpairs are shared (how electronsare sharedbetweenthe central atomandsurroundingatoms) 4. Determine the name of the molecular structure frompositions of the atoms Drawingthe Models: Dashes go behind/away,solidwedges go out/towards,solidlines are on the flat plan of the paper. Steric number—the areas where electrons are located/concentrated(bonds or lone pairs) 2 ***Inlab the Professor gave us achartthatshowedus the names of the molecular structures.I cannotcopy thatchartdue to copyrightrules butmake sure youstudy and reference thatchartwhenyoupractice usingthe VSEPRmodel.Below is alistof some of the structures andageneral description butthe chartwouldprobably do more good.*** Linear—one atomon bothsides (HCl or CO ) 2 Trigonal Planar—anatom in the middle withthree evenly branchedoutatoms (BH ) 3 Tetrahedral—atomin the middle withfour atoms spacedout109.5 Trigonal bipyramidal—atom in the middle withthree atoms alongthe equatorial plane and two onthe polar (top and bottom) Trigonal Pyramidal—three bondedpairs withone lone pair Octahedral—sixatoms branchingoutin 90 angles to eachother Bent—has 2bonded pairs and up to two lone pairs (water) T-Shaped—3 bondedpairs (in the shape of a T) and two lone pairs Seesaw—4bondedpairs (looks like aseesaw)andone lone pair Square Planar—4bondedpairs onequatorial plane and 2 lone pairs (XeF ) 4 3
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'