Gen Chemistry II
Gen Chemistry II CHEM 1030
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This 4 page Class Notes was uploaded by Aurore Armstrong on Wednesday October 28, 2015. The Class Notes belongs to CHEM 1030 at University of Wyoming taught by Michael Sommer in Fall. Since its upload, it has received 8 views. For similar materials see /class/230372/chem-1030-university-of-wyoming in Chemistry at University of Wyoming.
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Date Created: 10/28/15
University of Wyoming CHEMISTRY 1030 How to Draw a Molecular Lewis Structure 1 Obtain the molecular formula and draw the Lewis Dot Symbols for each atom in the formula 2 Determine how many electrons each atom needs to get an octet or quotduetquot for hydrogen this will roughly be the number of quotnormalquot covalent bonds the atom needs to make Note Elements with valence shells of n 2 3 can have expanded octets so this may not necessarily tell you how many bonds the atoms will definitely make 3 Determine the electronegativities of each atom in the molecular formula Note Atoms with high EN values tend to prefer making bonds to only one other atom 4 Place the atom that can make the most bonds andor the atom with the lowest electronegativity between the other atoms Notel Most elements exception carbon C do not like bonding to other atoms of the same element so try to avoid this in your atom arrangement Note2 Hydrogen should never be a centralized atom Note3 Hydrogen likes to bond to oxygen so if both are present there is a good chance they will be bonded Note4 Long extended molecules are not the most common unless carbon is involved 5 Connect the atoms with dashes corresponding to the bonding pairs of electrons and explicitly show all the lone pairs 6 Try to give as many atoms in the molecule as possible octets but do not worry if they do not all get one SOMMERil University of Wyoming CHEMISTRY 1030 How to Draw a Molecular Lewis Structure 10 Note In general the atoms that should get octets in order of preference F C O atoms with higher electronegativities eg N and Cl Decide whether coordinate covalent bonds are needed to give octets to the atoms that need them Note A coordinate covalent bond is one where both electrons come from the same atom If coordinate covalent bonds are present make sure to assign formal charges Notel You may use the formula below for assigning formal charges number of number of number fogmal valence covalent 2 of lone c urge electrons bonds pairs Note2 Generally speaking if you can get away with fewer andor smaller formal charges the Lewis structure is better If the molecule is an ion include both formal charges and net charge using a bracket around the molecule with the charge as a superscript Note The formal charges must sum up to the total ionic charge If resonance is indicated make sure to draw at least two resonance structures Note Resonance structures are drawn with double headed arrows separating them SOMMERiz Sommer s Handy Dandy Molecular Shape Table Generic Electronic Molecular Arrangement Hybrid Formula Geometry Geometry AX Linear Linear s 2 W 180 p X A X AX3 p Trigonal X Trigonal spz DA planar Xlt1200 planar D x AXZE X Bent spz A lt120 X AX4 Tetrahedral X Tetrahedral sp3 109 5 Auquot quotI 0 x X X AXSE o o Trigomal sp3 quotInquot Pyramidal X X lt1095 X AXZE2 X Bent sp3 ltlt109 5 A X AXS Trigonal X Trigonal sp3d Bipyramidal Bipyramidal 0A8 X Aquot 120gt O X 90 quot X AX4E X See Saw sp3d l X Aquot 120 gt180 X X AX3E2 X T Shape sp3d 90 X I Sommer s Handy Dandy Molecular Shape Table Generic Electronic Molecular Arrangement Hybrid Formula Geometry Geometry AXZE3 X Linear sp3d 180 IA 39 X AX6 O Octahedral X Octahedral sp3d2 QOI sX X7A39 X 0 X X AXSE X Square sp3d2 X Pyramidal X A 39 X 0 O AX4E2 X Square sp3d2 quot Planar AXnEm A is the central atom n is the number of atoms X bonded to A and m is the number of lone pairs E on atom A Note if E does not apper in the generic formula that means m0 no lone pairs If no subscript appears on X or E that means n or m 1
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