LAB: SHAPES OF COVALENT MOLECULES & POLARITY
Introduction:
The most common chemical bond between two atoms is a covalent bond.
The covalent bond consists of a pair of shared electrons, one from each atom. If this
pair of electrons is shared between two atoms of equal electro negativities, the bond
would be called a nonpolar covalent bond. However, in most cases, the pair of
electrons is shifted toward the more electronegative element. A partial negative
charge results on one side of the bond and a partial positive charge on the other.
This type of covalent bond is called polar covalent.
Molecules composed of covalently bonded atoms may also be polar or
nonpolar. For the molecule to be polar, it must, of course, have polar bonds. But
the key factor for determining the polarity of a molecule is its shape. If the polar
bonds (dipoles) are symmetrical around the central atom, they offset each other
and the resulting molecule is nonpolar. However, if the dipoles are not symmetrical
around the central atom, the electrons will be pulled to one end of this molecule and
the resulting molecule is polar.
Objectives:
(1) Predict each molecule’s shape using your knowledge of hybridization.
(2) Predict each molecule’s polarity on the basis of its shape.
Equipment:
Paper and pencil
Procedure:
1. Prepare a data table according to the directions in the Analysis section
below.
2. Complete your data table using the following compounds:
1. H2
5. SO3
9.
CH4
13. CH3Cl
2. HBr
6. CO2
10.
HClO
14. HCOOH
3. H2O
7. H2CO
11.
O2
15. CO32-
4. NH3
8. C2H2
12.
AlH3
16. NH4+
Analysis:
Prepare a table for recording data for each of the 16 molecules. Include the
following in your table: the formula, the Lewis dot structure, shared electron pairs,
unshared electron pairs, total electron pairs, bonding orbitals, molecular shape,
structural formula, and polarity. Use the table below as a guide:
Formula
HCl
Lewis
Shared
Unshared
Total
Molecular
Structural
Structure
e-Pairs
e- Pairs
e-Pairs
Shape
Formula
H – Cl :
1
0
1
Linear
H – Cl
Polarity
Polar
Further Investigations:
1.
On the basis of this experiment and your classwork, predict the
a. type of bonding
b. molecular shape
c. molecular polarity
for each of the following compounds (construct a table):
2.
(1)
HBr
(3)
BaCl2
(5)
CI4
(2)
SCl2
(4)
NH3
(6)
AlH3
Calculate the electronegativity difference and indicate the type of bond for
the following attractions:
(a)
Na - Br
(c)
Se – O
(e)
Mg – Cl
(b)
3.
C-H
(d)
Br – Br
What does the term isomer mean?
(f)
Al - I
Key
Formula
Lewis
Shared
Unshared
Total
Molecular
Structural
Structure
e-Pairs
e- Pairs
e-Pairs
Shape
Formula
1
0 or 3
1 or 4
Linear
H – Cl
Polar
1
0 or 3
1 or 4
Linear
H – Br
Polar
2
2
4
Bent
HCl
HBr
H2O
H Br
Polarity
Polar
Trigonal
NH3
3
1
4
Pyramid
Polar
al
SO3
3
0
3
CO2
2
2
4
H2CO
3
0
3
C2H2
2
0
2
CH4
4
0
4
HClO
2
2
4
Trigonal
Non
Planar
Polar
Linear
Polar
Trigonal
Planar
Linear
Polar
Non
Polar
Tetra
Non
hedral
Polar
Bent
Polar
O2
AlH3
Ionic
CH3Cl
HCOOH
Omit
2
2
4
Ionic
Ionic
Ionic
4
0
4
3
0
3
Linear
Non
O–O
Polar
Crystal
Ionic
Lattice
Tetra
Polar
hedral
Trigonal
Polar
Planar
O
CO32-
3
0
3
NH4+
4
0
4
Trigonal
Planar
O
C
Non
O
Polar
Tetra
Non
hedral
Polar
Further Investigation
1. On the basis of this experiment and your classwork, predict the
a. type of bonding b. molecular shape
c. molecular polarity
for each of the following compounds (construct a table):
(1)
HBr
(3)
BaCl2
(5)
CI4
(2)
SCl2
(4)
NH3
(6)
AlH3
Compound
Bond
Molecular
Polarity
Type
Shape
HBr
Covalent
Linear
Polar
SCl2
Covalent
Bent
Polar
2.
BaCl2
Ionic
Crystal Lattice
Ionic
NH3
Covalent
Trigonal Pyramidal
Polar
CI4
Covalent
Tetrahedral
Non-Polar
AlH3
Ionic
Crystal Lattice
Ionic
Calculate the electronegativity difference and indicate the type of bond for
the following attractions:
(a)
Na - Br
(c)
Se – O
(e)
Mg – Cl
(b)
C-H
Elements
(d)
Br – Br
Electronegativity
(f)
Al - I
Bond Type
Difference
3.
Na - Br
Ionic
C-H
Covalent (Non-Polar)
Se – O
Covalent (Polar)
Br – Br
Covalent (Non-Polar)
Mg – Cl
Ionic
Al - I
Ionic
What does the term isomer mean?
Any of two or more compounds, radicals, or ions that contain the same
number of atoms of the same elements but differ in structural
arrangement and properties.
Example