What’s Cookin                          LAB 2                          Fall 2005

 

Molecular Models and the Shapes of Molecules

 

 

Purpose

          In this lab we will gain an understanding of the 3-dimensional nature of molecules.  This will be accomplished with the use of molecular models.  A number of different molecules of assorted shapes and bonding motifs will be assembled.

 

 

 

Introduction

          Chemical bonding permits us to understand why two atoms remain at a fixed position relative to one another in a molecule.  The overall arrangement of chemical bonds give rise to the 3-dimensional structure of a molecule. 

 

          Molecular models are sufficient and sometimes preferred when trying to get an idea of the shape of a simple molecule, or part of a more complex system such as the metallo part of a metalloprotein.  Also an understanding of the arrangement of atoms relative to one another like the chirality of a carbon center can readily be determined as R or S with molecular models.

 

          There are many different types of molecular modeling kits available.  The type that an individual utilizes is somewhat driven by personal choice and the availability of funds.  Today you will use MY models, please handle them with care.  The green hollow sticks are supposed to be the chemical bonds.  The colored solid little pronged pegs represent atoms.  White is the hydrogen atom and black is carbon.  Red is an oxygen atom, blue is nitrogen and yellow & green are the halides.  Though these colors are only suggested, it is best to follow some of these traditional color assignments when building molecular models. 

         

 

Procedures

 

General description of our plan today.

We will organize ourselves into small groups of 2 people.  Each group will assemble the molecules listed in the text below.  When the molecule is built and sketched in 3 dimension by all group members, then proceed on.  Please keep your molecule kits organized and take a look at the text by Linus Pauling and Roger Hayward. 

 

Locate the H2 molecule.  You will draw the Lewis structures showing the VSEPR representation in the result section down below.  Try and accurately do it so it looks real.

 

We will repeat this procedure now for these molecules:

 

a.  H2           b.  Br2    c.  HBr

 

 

 

d.  H2O                e.  NH3   f.  BH3

         

 

 

 

g.  CH4          h.  CH3OH          i.  C2H6 

 

 

 

 

j.  CH3 CH2OH          k.  NH4+ l.  OH-  

 

 

 

 

m.  CH3NH2                        n.  C6H12  (no double bonds)

 

 

 

 

This next part gets us to molecules that have more than just single bonds.

  o.  O2                     p. C2H4                    q.  C2H2              r.  C6H6