LAB_08_LewisStructureLabDGCF09 - Pre-lab Assignment...

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Pre-lab Assignment Structures using Models, Lewis Structures and VSEPR Method You are asked by your instructor to construct a model of the CH 2 Cl 2 molecule. Being of a conservative nature, you proceed as directed in the section on Experimental Procedure. 1. First you need to find the number of valence electrons in CH 2 Cl 2 . The number of valence electrons in an atom element is equal to the group number of that element in the Periodic Table. C is in Group _______ H is in Group _______ Cl is in Group _______ In CH 2 Cl 2 there is a total of __________ valence electrons. (Outer shell electrons only.) 2. The model consists of balls and sticks. (1 stick =2 electrons, 1 hole will connect to 1 stick.) What kind of ball (# of holes) should you select for the C atom? ____________ the H atoms? ____________ the Cl atoms? ____________ The electrons in the molecule are paired, and each stick represents an electron pair. How many sticks do you need? ___________ 3. Assemble a skeleton structure for the molecule, connecting the balls with sticks into one unit. Use the rule that C atoms form four bonds, whereas Cl atoms usually do not. Draw a sketch of the ball and stick skeleton in your lab book: 4. How many sticks did you need to make the skeleton structure? __________ How many sticks are left over? __________ If your model is to obey the octet rule each ball must have four sticks in it (except for hydrogen atoms balls, which need only one). (Since each atom in an octet rule species is surrounded by 4 pairs of electrons.) How many holes remain to be filled? _________ Fill them with the remaining sticks, which represent nonbonding electron pairs. In your lab book, draw the complete Lewis structure for CH 2 Cl 2 using lines for bonds and pairs of dots for nonbonding electrons. 5. In your lab book, describe the implied geometry of the central atom and the approximate bond angles of CH 2 Cl 2 .
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10/08 DGC 1 Stru c tur e s u s ing Mod e l s , L e wi s Stru c tur e s and VSEPR M e thod 1 Many years ago it was observed that in many of its compounds the carbon atoms formed four chemical linkages to other atoms. As early at 1870, graphic formulas of carbon compounds were drawn as shown: methane Although such drawings as these would imply that the atom-atom linkages, indicated by valence strokes, lie in a plane, chemical evidence, particularly the existence of only one substance with the graphic formula requires that the linkages be directed toward the corners of tetrahedron, at the center of which is the carbon atom. The physical significance of the chemical linkages between atoms, expressed by the lines or valence strokes in molecular structure diagrams, became evident soon after the discovery of the electron. In 1916 in a classic paper, G.N. Lewis suggested, on the basis of chemical evidence, that the single bonds in graphic formulas involve two electrons and that an atom tends to hold eight electrons in its outermost or valence shell.
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LAB_08_LewisStructureLabDGCF09 - Pre-lab Assignment...

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