MOLECULAR STRUCTURE; LEWIS STRUCTURES AND 3-D MODELS

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of real molecules. A good way to achieve this understanding or translation from 2-D to 3-D is the use of molecular models, though these are still far from giving the true picture of real molecules.

1 Chemistry Name(s) MOLECULAR STRUCTURE; LEWIS STRUCTURES AND 3-D MODELS INTRODUCTION: Chemists are often concerned with molecular structure. It is helpful and useful to have a good understanding of the relationship between the twodimensional, flat molecular structures seen in texts and the better perspective or three-dimensional picture of real molecules. A good way to achieve this understanding or translation from 2-D to 3-D is the use of molecular models, though these are still far from giving the true picture of real molecules. As the textbooks frequently show, Lewis structures can be drawn if the molecular formula is given and certain rules for number and placement of electrons are followed. From the Lewis structure for a molecule, a 3-D model can be constructed to give a better (though not perfect) picture of the real molecule. In this experiment the formula of a molecule or molecular ion will be given. An acceptable Lewis structure will be drawn based on that formula. A 3-D model of that molecule or molecular ion will then be constructed using a molecular model kit. An exact 3-D or perspective drawing based on the 3-D model will then be made. Before performing the experiment review the material in the textbook on Lewis structures, VSEPR, bond lengths, and single and multiple bonds. SUPPLEMENTARY INFORMATION A. Review the rules for drawing Lewis structures based on the given formula. 1. Determine the total number of valence electrons in the formula. 2. Apply the octet rule if possible (except for H) to each atom. Keep in mind that there are exceptions to the octet rule. 3. If too few electrons are available, multiple bonding may be necessary and if that is the case, resonance may also be possible. B. The valence shell Iectron Eair.epulsion Theory (VSEPR) is used to determine the geometry of the regions of electron density (electrons pairs or an effective region where two or more electrons pairs are).

C. Drawing 3-D Drawing 3-D or trigonal bipyramidal or Two of examples perspective structures octahedral geometries the techniques are of molecules with is difficult, but possible.

ModelA the line the bond just touching the circle of atom. is in front of the plane of the and is shown by the line connecting it into the circle around C.

2 C. Drawing 3-D Drawing 3-D or trigonal bipyramidal or Two of examples perspective structures octahedral geometries the techniques are of molecules with is difficult, but possible. shown for somewhat tetrahedral, the methane molecule, CH4. The by circles. The for identification only. in the plane central atom. In models Aand B, H1, C, and H2 are in the plane. ModelA the line the bond just touching the circle of atom. is in front of the plane of the and is shown by the line connecting it into the circle around C. atoms are represented atoms as possible Place as many representing paper same same each subscripts are as the H3 shows H4 is behind the of and is shown by the line into around H4 and just touching the circle around C. plane the paper the circle Model B positions of idea the to the diagram below closer that atoms shows perspective by using wedge shaped bonds to show in front or behind the plane of paper. This is on the larger. This means that the end of bond is larger than the end from the observer. The end a to be to than end b. closer objects are observer shows closer the farthest the observer based the

3 THE EXPERIMENT Work in groups of 2, 3, or 4. student may work alone. If sufficient model kits are available, each Using the model kit provided, determine the required information from the list of formulas given below. Write and draw all information directly on the REPORT pages. What to Find: 1. Total number of valence electrons in the molecule or molecular ion. 2. Draw a Lewis structure of the molecule or molecular ion. 3. Determine the geometry around the central atom(s) and build an accurate model of the molecule or molecular ion using the model kit available. 4. Draw an exact 3-D perspective picture of the molecule or molecular ion based on the model constructed in 3 above. The Formulas to be investigated 1. Br N 4. CH 5. NH 6. CO2 7. HCO 8. C4H80 (chain of 4 C) 9. C6Hi (6 C s in a ring) 10. C2H5OH Questions (answer on a separate sheet): 1. Which molecules were nonpolar because all of the bonds were nonpolar? 2. Which molecules had polar covalent bonds but were nonpolar because of symmetry? 3. Which molecules were polar? 4. What geometries produced polar molecules?

4 Laboratory Report Sheet Chemistry Name(s) MOLECULAR STRUCTURE; LEWIS STRUCTURES AND 3-D MODELS 1. Molecular Formula Total Valence Electrons 2. Molecular Formula Total Valence Electrons

5 3. Molecular Formula Total Valence Electrons 4. Molecular Formula Total Valence Electrons

6 5. Molecular Formula Total Valence Electrons 6. Molecular Formula Total Valence Electrons

7 7. Molecular Formula Total Valence Electrons 8. Molecular Formula Total Valence Electrons

8 9. Molecular Formula Total Valence Electrons 10. Molecular Formula Total Valence Electrons

Chapter 13: Phenomena

Chapter 13: Phenomena Phenomena: Scientists measured the bond angles of some common molecules. In the pictures below each line represents a bond that contains 2 electrons. If multiple lines are drawn together