Chem1212K, Week 3 Notes
Chem1212K, Week 3 Notes CHEM 1212K
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This 3 page Class Notes was uploaded by Bethany B. on Tuesday September 6, 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 4 views. For similar materials see Principles Chemistry II w/Lab in Chemistry at Georgia Gwinnett College.
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Date Created: 09/06/16
9.6.16 Chemistry 1212KNotes[Week 3] Chapter 10 Lecture Cont. MolecularPolarity Question:Why are some molecules polar in natures andother are nonpolar? Answer:Lookattheir intramolecular bondingandtheir three-dimensional structures (geometries). Inorder for molecules to be polar,the followingcriteriamustbe met: o There must be polar covalent bonds withinthe molecule. o The molecule must have anetdipole moment, because the molecule’s geometry is not symmetric. The netdipole moment is due to a difference inbondatoms’ electronegativities. Exceptions:1lone pair=asymmetrical,2 lone pairs=symmetrical,3 Dipole Moment—the directionwherethe electrons are beingpulled to.Polar molecules have “net”dipole moments. o Example: H—F the “Dipole”is the arrow pointingtowards the Fluorine atom because that is where the electrons are beingpulledtowards. Symmetric molecules do not have adipole moment. o These molecules are nonpolar. Example: CO 2 Asymmetric molecules do have adipole moment. o These molecules are polar. Example: H 2 The more polar something is;the better solventitwill be inwater. Practice:Whichone is polar? a) Hexane (C H6)14 b) Benzene (C H6)6 c) Acetone (C H3O6 d) Chlorine (Cl2) e) XeF 4 f) SF6 Hybridization HybridOrbitals are formedby combining the s p and z orbitals. Onthe table for the VSEPRchart,the Orbital Type is the hybridorbital. Chapter 11 Notes IntramolecularBonding “Within”the molecule Molecules are formedby sharingelectronsbetweenthe atoms Intermolecular Bonding “InBetween”molecules Dipole-dipole forces o hydrogenbonds holdingtwo watermolecules together London dispersion forces Intramolecularbonds are strongerthan intermolecular forces o Intramolecularbonds are strongerbecause itwouldtake alotmore energy to overcome covalentbonds andbreak apartthe molecule than to overcome intermolecularforces inbetweenmolecules. o Scotchtape or ducttape workby strong intermolecularforces. Ion-dipole Forces—polarwater molecules dissolve ionic NaCl molecules. o H 2 has a concavemeniscus while Hghas a convex.This happens because H O2has hydrogenbonds withthe glass molecules while Hgdoes not have any hydrogenbonds withthe glass molecules. o DNA has hydrogenbonds betweenthe A-Tand such,whichis whatgives it the double helixshape. Look up“The Inner Life of the Cell”videoonYouTube. Forces: Hydrogenbonding Strongdipole-dipole forces Hydrogenis bound to a highly electronegative atom—nitrogen,oxygen,or fluorine. Dipole-Dipole Forces Dipole moment—molecules withpolar bonds oftenbehaveinanelectric fieldas if they had a center of positivecharge andacenter of negative charge Molecules withdipole moments canattracteachother electrostatically.They line up so that the positive andnegativeends are close to eachother. Only about1% as strongas covalentor ionic bonds. DispersionForces Instantaneous dipole thatoccursaccidentally inagivenatominduces asimilar dipole in a neighboringatom. Significantin large atoms/molecules Occurs in all molecules,includingnonpolar ones. These are the small dipole moments thatevery molecule has. Ion-Dipole Forces 2 Occur whenanionic compoundis mixed witha polar compound. o Ex: NaCl is dissolvedinwater. Review: Differenttypes of intermolecularforces: o Dipole-dipole forces(basedondipole moments) o Hydrogenbonding(H-atom to an electronegative atom—very important in biology (only withFON:fluorine,oxygen,nitrogen)) o London dispersionforces(all molecules) o Ion-Dipole forces (ions inpolar solvents Strength:Ion-Dipole >>> H-Bonding>Dipole-Dipole >Dispersion o CovalentOnly Meltingandboilingpoints of molecules will be dictatedby intermolecular forces and their interactions:“the strongerthe intermolecularforces,the higher the melting and boilingpoints” Ion-Dipole: H-Bonding: KCl HF MgS NH 3 NaBr HNO 2 N 31 CH 3H + NH 4 OH - + H 3 Dipole-Dipole: Dispersion(only): CO SiO4 HCl F2 H 2 BH 3 CH 4 CF 4 CS 2 CCl 4 **Practice matchingthe molecules withtheir intermolecular forces for the test! Whichhas a higher melting point? CS 2 or CCl 4 Because Cl is more electronegative than S, it w ill be stronger CH 4 or NH 3 CHCl 3r CF 4 H2S or CH 4 3
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