Molecular Models Lab Directions Please Return! Directions: Use the following information to create your lab report in the classwork section of your notebook. Include the following sections

A. Title B. Purpose: (summaries in 1-2 sentences) C. Data D. Analysis Questions E. Conclusion

Background: You can represent a molecule on paper with either a molecular formula or a structural formula. However, molecular formulas, such as NH3, provide no information concerning the actual arrangement of atoms in the molecule. Structural formulas, such as Lewis dot structures/Electron dot structures, give some information about the arrangement of atoms in the molecule. However, these structural formulas provide only limited information because they are two-dimensional (2D). Actual molecular shapes are three-dimensional (3D). A molecular model is far superior to a structural formula when it comes to visualizing atomic arrangement. Compared to molecular formulas and structural formulas, molecular models provide much more information about the true shapes of molecules. In this experiment, you will use ball-and-stick models to help you visualize the shapes of molecules. Each kit includes wooden sticks which are to be used to make single covalent bonds. Springs are used to make double and triple covalent bonds. Colored balls are used to represent different elements according to Table 1. The balls are drilled with holes to accept sticks or springs; the number of holes in a ball reflect the maximum number of bonds a given atom can form. VSEPR (Valence-Shell Electron Pair Repulsion) is an important concept defining molecular geometry. Lewis dot/electron dot structures are used to see the numbers of shared and unshared electron pairs around the central atom. Based on the number of shared (bonded) and unshared (non-bonded) electron pairs in the valence or outer “shell” area of the central atom, the 3D arrangement can be determined. Multiple bonds – double and triple – are treated as only one bond for this purpose. Use the following chart to determine molecular shape.

Table 2

Linear Bent Trigonal Planar

Trigonal Pyramidal

Tetrahedral Trigonal

Bipyramidal octahedral Square

planar

   

 

P

F

F F

F F

   

 

   

Cl

BCl Cl

       

Kr

F

F F

F  

Table 1

Color Atoms # of Holes

Maximum # of bonds

Black C 4 4 Blue N & P 3 3 Yellow H 1 1 Red O & S 2 2 Green Cl 1 1 Orange Br 1 1 Purple F & I 1 1

Procedure: 1. Read the background material and come up with a purpose. 2. Draw first row of your table. You will need to leave enough space for Lewis dot structures. 3. For each molecule in the data chart first calculate the total number of valence electrons. 4. Draw the complete Lewis dot structure in your data table. 5. Use Table 1 to build the molecule. 6. Use Table 2 to determine the shape of each molecule. NOTE: If working in a group of 2 or 3, each person can make a different molecule and share what they find with the group so that not every person makes every molecule, but everyone is working at the same time.

Data: you will need plenty of space for your Lewis dot structures so do not draw the whole table at once, draw each row as you go so you know how much space you need.

Formula Total #Valence Electrons Lewis Dot Structure 3D sketch Name of 3D

shape

H2O

NH3

CH4

H2S

CCl4

CCl2F2

C2H6

N2

CO2

H2CO

C4H10

CO(NH2)2

Questions:

1. Which of the molecules have double bonds? 2. Which molecule has a triple bond? 3. Which molecule is diatomic? 4. How does a molecular formula differ from a structural formula (see background). 5. Explain the significance of the VSEPR molecular geometry model.

Conclusions: Explain what you learned from this lab activity?