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Experiment 11 - Molecular Models

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									Experiment 11 – Molecular Models                                    Name __________________
                                                               Lab Section __________________

                               Experiment 11 – Molecular Models
Introduction

When two or more nonmetals come together to form a compound, they do so using covalent bonds. In
a covalent bond the valence electrons are shared between the atoms. The valence electrons are the
outermost electrons, those found in the outermost, or valence shell. When the atoms come together
and share their valence electrons, they will do so in such a way as to fill this octet: having 8 electrons
surrounding the atom. The only exception to this is hydrogen, which only needs 2 electrons to fill its
outermost shell.

The groups of elements each contribute their own number of valence electrons to the compound. The
noble gases have a full 8 electrons in their valence shells, and hence have no need to form bonds to
fulfill their octet. Elemental groups 17, 16, 15, and 14 each have 7, 6, 5, and 4 valence electrons,
respectively. Hydrogen has only 1 valence electron. In turn this means that group 14wants 4 bonds,
group 15 wants 3 bonds, group 16 wants 2 bond, and group 17, and hydrogen, want one bond, to
satisfy their octet.

In this experiment you will draw the electron dot and structural formulas of molecules based on
molecular models that you will build. You will use sticks, balls, and springs to build a molecule based
on the atoms that make up the compound. Each stick or spring will represent 2 electrons, and the
number of holes in the ball will represent the number of bonds that that element wants to make. As
you will see in this lab, carbon wants 4 bonds, nitrogen wants 3 bonds, oxygen wants 2 bonds, and the
halogens and hydrogen want 1 bond. Each pair of electrons represents a bond.

When drawing the electron dot and structural formulas, all of the valence electrons will be used to
fulfill each atom’s octet. The total number of valence electrons used will be the sum of all of the
valence electrons of all the atoms in the molecule. Pairs of electrons that form bonds are called
bonding electrons, while those pairs not involved in bonding are called lone pairs. The electron dot
formula will use dots to represent both bonding and lone pair electrons. The structural formula will
use a line will represent a pair of bonding electrons, while lone pairs will still be represented as dots.

In this experiment, each of the elements will be represented as a colored ball as follows:

       Black – Carbon                 Blue – Nitrogen                Red – Oxygen

       Yellow – Hydrogen              Green – Chlorine               Orange – Bromine

       Purple – Iodine or Fluorine

Each bond will be represented by connectors as follows:

       Wooded sticks – single bonds           Springs/Plastic tubing – Double/Triple bonds
Experiment 11 – Molecular Models                                      Name __________________
                                                                 Lab Section __________________
Examples

Consider the following compound, CH2Cl2. When it is built, it will look like Figure 11.1:

                           The total number of valence electrons is:

                                   1 C → 1 × 4 = 4 e-
                                   2 H → 2 ×1 = 2 e-
                                   2 Cl → 2 ×7 = 14 e-
                                   Total Valence = 20 e-

                           Notice that carbon has 4 bonds and the chlorine and hydrogen each have 1
                           bond, as expected.

The structural formula and the electron dot formulas will be written as follows:




Notice that all valence electrons are used in constructing these models and every octet is satisfied.

Consider the following compound, CH2O. When built, it will look like Figure 11.2:

                     The total number of valence electrons is:

                            1 C → 1 × 4 = 4 e-
                            2 H → 2 ×1 = 2 e-
                            2 O → 1 ×6 = 6 e-
                            Total Valence = 12 e-

                     Notice that carbon has 4 bonds, the oxygen has 2 bonds, and hydrogen each have 1
bond, as expected.

The structural formula and the electron dot formulas will be written as follows:

              :O:                         : O:
                                       H : :C : H
                                           :
         H      C      H
Notice that all valence electrons are used in constructing these models and every octet is satisfied.
Experiment 11 – Molecular Models                                    Name __________________
                                                               Lab Section __________________
Consider the following compound N2. When built, it will look like Figure 11.3:

                               The total number of valence electrons is:

                                       2 N → 2 × 5 = 10 e-
                               -

                                       Total Valence = 10 e-

                               Notice that nitrogen has 3 bonds as expected.

The structural formula and the electron dot formulas will be written as follows:


          : N N:                      : N ::: N :


Notice that all valence electrons are used in constructing these models and every octet is satisfied.




Procedure

   Build the molecules listed on the following pages and draw them.

   Draw the electron dot formula. Add lone pair electrons to any atom needing their octet satisfied.

   Draw the structural formula. Include lone pairs in the drawing.

   Calculate the total number of valence electrons for the molecule and verify that the correct
   numbers of electrons were used in building the electron dot and structural formulas.
Experiment 11 – Molecular Models                                 Name __________________
                                                            Lab Section __________________
Prelaboratory Questions

1) Please define the following terms

Valence electrons


Covalent bond


Single bond


Double bond


Triple bond


Lone pair electrons


2) How many valence electrons are in the following molecules?

O2                    CHCl3                 C3H8



HCl                   PCl3                  CO2


3) Consider the following molecule. Write the electron dot and structural formulas, and calculate the
total number of valence electrons for the molecule.
Experiment 11 – Molecular Models                      Name __________________
                                                 Lab Section __________________
Data Table
Molecules with Single Bonds
 Molecule             Model        Structural Formula     Electron Dot Formula


    H2

Valence e-




    F2

Valence e-




    Cl2

Valence e-




    Br2

Valence e-




    I2

Valence e-
Experiment 11 – Molecular Models                      Name __________________
                                                 Lab Section __________________



 Molecule            Model         Structural Formula     Electron Dot Formula


   HCl

Valence e-




   H2O

Valence e-




   HOCl

Valence e-




  H2O2

Valence e-




  CH4

Valence e-
Experiment 11 – Molecular Models                      Name __________________
                                                 Lab Section __________________



 Molecule            Model         Structural Formula     Electron Dot Formula


 CH2Cl2

Valence e-




  CF4

Valence e-




  NH3

Valence e-




  N2H4

Valence e-




 CH3OH

Valence e-
Experiment 11 – Molecular Models                      Name __________________
                                                 Lab Section __________________
Molecules with Double Bonds

 Molecule            Model         Structural Formula     Electron Dot Formula


   O2

Valence e-




  C2H4

Valence e-




 C2H3Cl

Valence e-




 HONO

Valence e-




 HCOOH

Valence e-
Experiment 11 – Molecular Models                               Name __________________
                                                          Lab Section __________________



 Molecule            Model                 Structural Formula         Electron Dot Formula


   CO2

Valence e-




   C3H4

Valence e-




 HC2NH2

Valence e-




CH3COOH

Valence e-




Valence e-




      * This compound will appear to violate the rule of number of bonds
Experiment 11 – Molecular Models                      Name __________________
                                                 Lab Section __________________
Molecules with Triple Bonds

 Molecule             Model        Structural Formula     Electron Dot Formula


    N2

Valence e-




   HCN

Valence e-




   C2H2

Valence e-




  HOCN

Valence e-
Experiment 11 – Molecular Models                      Name __________________
                                                 Lab Section __________________



 Molecule            Model         Structural Formula     Electron Dot Formula


Unkown 1

Valence e-




Unkown 2

Valence e-




Unkown 3

Valence e-




Unkown 4

Valence e-




Unkown 5

Valence e-
Experiment 11 – Molecular Models                                  Name __________________
                                                             Lab Section __________________
Postlaboratory Questions

 Molecule               Model                 Structural Formula         Electron Dot Formula


   H2S

Valence e-




    CS2

Valence e-




   CCl4

Valence e-




    PH3

Valence e-




         *
    O3

Valence e-




         * This compound will appear to violate the rule of number of bonds
Experiment 11 – Molecular Models                               Name __________________
                                                          Lab Section __________________


 Molecule            Structural Formula                      Electron Dot Formula


   NO3-      *




Valence e-




   CO32-       *




Valence e-




  NH4+     *




Valence e-




   CN-   *




Valence e-




   ClO3-       *




Valence e-




      * This compound will appear to violate the rule of number of bonds

								
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