Name _______________________________________
Period _____
Chemical Bonding: Shapes of Molecules & Bond Polarity
A covalent bond is formed when two atoms share a pair of electrons. If the pair of
electrons is shared equally between atoms the bond is referred to as a nonpolar covalent
bond. If the electrons are not equally shared, because one of the atoms has a greater
ability to attract electrons than the other, the bond is said to be a polar covalent bond.
Polar bonds have a negative end towards the electron-attracting atom and a positive end
toward the other atom.
Electronegativity is the measure of the electron-attracting ability of an atom for the
shared pair of electrons in a covalent bond. The electronegativity difference between the
two atoms that share the electrons gives an indication on the bond type between them. If
the difference is 0.0 – 0.4 the covalent bond is essentially nonpolar, and if the difference
is 0.4-1.8 the bond is polar. If the difference is greater than 1.8, the bond formed is
ionic. However, these ranges are only guidelines.
The way atoms bond together determines the shape of the molecule. Some common
shapes of simple molecules include:
Linear: atoms in a straight line
Bent: atoms in the same plane but not in a straight line
Pyramidal: pyramid-shaped with no central atom
Tetrahedral: tetrahedron-shaped with a central atom
Procedure:
1. Using a molecular model kit, construct the first set of molecules and complete the
table while viewing the model. Use sticks for single covalent bonds and springs
for any double or triple bonds. For sulfur use the red atoms and for fluorine use
orange or purple atoms. Remember that each stick or spring represents two
electrons being shared by the atoms they join.
2. After you have finished Set I, have your instructor check your models and chart
before moving on to Set II.
3. Complete Set II and Set III as you did Set I.
Note: These models show molecular shape. A Lewis dot structure often does not
properly represent shape since the drawing is two-dimensional. On the other hand, dot
diagrams show pairs of unshared electrons (lone pairs).
Set I:
Molecule
HI
Bond Type
(polar or
nonpolar)
H-I
Total
# of Valence
Electrons
Lewis Dot
Structure
Molecular
Shape
hydrogen iodide
Br2
Br-Br
bromine
O2
O-O
oxygen
BrCl
Br-Cl
bromine chloride
CO
C-O
carbon monoxide
HBr
H-Br
hydrogen
bromide
N2
N-N
nitrogen
HINT: One molecule needs a double bond and two molecules need triple bonds.
Set II:
Molecule
H2S
Bond Type
(polar or
nonpolar)
H-S
Total
# of Valence
Electrons
hydrogen sulfide
CO2
C-O
carbon dioxide
NF3
N-F
nitrogen trifluoride
SCl2
S-Cl
sulfur dichloride
O3
O-O
ozone
CF4
C-F
carbon
tetrafluoride
OF2
O-F
oxygen difluoride
HINT: Two molecules need double bonds.
Lewis Dot
Structure
Molecular
Shape
Set III: Start with methane, CH4, and adjust it to make CH3Cl and CH2Cl2.
Molecule
CH4
Bond Type
(polar or
nonpolar)
C-H
Total
# of Valence
Electrons
Lewis Dot
Structure
Molecular
Shape
methane
CH3Cl
C-H
chloromethane
C-Cl
CH2Cl2
C-H
dichloromethan
C-Cl
e
Questions:
1. Calculate the electronegativity difference and give the % ionic character for each
of the following bonds (look up electronegativity values on periodic table).
Bond type
A.
B.
C.
D.
E.
EN
difference
% ionic
character
H-O
N-H
H-Cl
Br-Cl
H-S
Bond type
EN
difference
% ionic
character
F. Cl-Cl
G. C-O
H. K-Br
I. Na-O
J. S-O
2. Classify each of the following as an ionic or covalent compound.
Molecule
A.
B.
C.
D.
F2
MgCl2
CCl4
HCl
Type
E.
F.
G.
H.
Molecule
CO2
H2O
KI
BaBr2
Type
3. Both water and carbon dioxide are triatomic molecules. Explain why one of these is
bent & the other in linear. (Drawing the Lewis dot structures may help to explain this.)