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 e2 H → 2 ×1 = 2 e2 Cl → 2 ×7 = 14 eTotal Valence = 20 eNotice 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 e2 H → 2 ×1 = 2 e2 O → 1 ×6 = 6 eTotal Valence = 12 eNotice 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 eNotice 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
H2
Valence e-
F2
Valence e-
Cl2
Valence e-
Br2
Valence e-
I2
Valence e-
Model
Structural Formula
Electron Dot Formula
Experiment 11 – Molecular Models
Molecule
HCl
Valence e-
H2O
Valence e-
HOCl
Valence e-
H2O2
Valence e-
CH4
Valence e-
Model
Name __________________
Lab Section __________________
Structural Formula
Electron Dot Formula
Experiment 11 – Molecular Models
Molecule
CH2Cl2
Valence e-
CF4
Valence e-
NH3
Valence e-
N2H4
Valence e-
CH3OH
Valence e-
Model
Name __________________
Lab Section __________________
Structural Formula
Electron Dot Formula
Experiment 11 – Molecular Models
Name __________________
Lab Section __________________
Molecules with Double Bonds
Molecule
O2
Valence e-
C2H4
Valence e-
C2H3Cl
Valence e-
HONO
Valence e-
HCOOH
Valence e-
Model
Structural Formula
Electron Dot Formula
Experiment 11 – Molecular Models
Molecule
Model
Name __________________
Lab Section __________________
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
N2
Valence e-
HCN
Valence e-
C2H2
Valence e-
HOCN
Valence e-
Model
Structural Formula
Electron Dot Formula
Experiment 11 – Molecular Models
Molecule
Unkown 1
Valence e-
Unkown 2
Valence e-
Unkown 3
Valence e-
Unkown 4
Valence e-
Unkown 5
Valence e-
Model
Name __________________
Lab Section __________________
Structural Formula
Electron Dot Formula
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
Molecule
NO3-
Structural Formula
Name __________________
Lab Section __________________
Electron Dot Formula
*
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