Chapter 9
Covalent Bonding
9.1 The Covalent Bond
The chemical combination of two or more non-metal
atoms through the sharing of valence electrons
Molecule
Single Covalent
Double Covalent
Triple Covalent
Why Do Atoms Bond?
Atoms bond to establish a stable electron
configuration for each atom in the bond.
******Remember the Octet Rule*******
Atoms gain, lose or share electrons in order to acquire a
full set of 8 valence electrons (noble gas configuration)
Covalent Bonds
Single Bonds

Each atom in the bond shares one of its electrons
Single covalent bonds are also called Sigma Bonds. Sigma bonds
are the result of atomic orbital overlapping “end on end”
Double Bonds
 Each atom in the bond shares two of its electrons
Triple Bonds
 Each atom in the bond shares three of its electrons
Double and Triple covalent bonds contain one Sigma Bond. The
Remaining bond(s) are called pi bonds. Pi bonds are the result of
Parallel overlapping of atomic orbitals.
Strength of Covalent Bonds
The strength of a covalent bond is determined
by the distance between nuclei of each
bonding atom (Bond Length)
Bond length is directly proportional to
Bond Strength
Single<Double<Triple
9.1Naming Molecules
REFER TO CHAPTER 9 PACKET
You should be able to name binary
molecular compounds and acids (binary
and oxyacids)
How to Draw a Lewis Structure

Predict the location of atoms
1.
If there are more than two atoms, place the least electronegative atom in the
center and surround it by the remaining atoms.
2.
Hydrogen is always terminal (outside) because it can only make one bond

Determine the total number of electrons if each atom had a full set of valence
electrons (2 for H, 8 for all others)

Add up the number of valence electron that you have to work with

Subtract total valence electrons from total electrons and divide by two. This is
the number of bonding pairs that are needed to put together the molecule.

Connect the atoms with the number of bonds that you calculated above

Add lone pairs where needed so that each atom has a full octet (except for
hydrogen which can only have two electrons)
Molecule
HCN
Total Electrons
Valence Electrons Bonding Pairs
Polyatomic Ions
Polyatomic ions are a cluster of non-metals that carry a charge.
To draw the structure of a polyatomic ion, follow the procedure
for drawing ordinary molecules but add or subtract the
number of electrons gained or lost to the total number of
valence electrons in your structure as indicated by the charge
on the ion.
Molecule
IO3-
Total Electrons
Valence Electrons
Bonding Pairs
Resonance Structures
Def: A condition when more than one valid Lewis
structure can be written for a molecule or ion.
Exceptions to the Octet Rule

Too few electrons surrounding the central atom (ex: BH3)
Boron will not have a full octet, only 6 electrons. It can only achieve a full
octet when another atom shares an entire pair of electrons with it
(Coordinate covalent bonding)

Too many electrons surrounding the central atom (ex: PCl5)

An odd number of electrons
Molecular Shape (VSEPR)
Valence Shell Electron Pair Repulsion – minimizes the repulsion of
shared and unshared pairs of electrons around the central atom.




The shape of a molecule determines many of its physical and
chemical properties.
The VSEPR is based on the arrangement of bonding and lone
electrons around a central atom to minimize repulsion.
The repulsion of electrons creates a specific bond angle between a
central atom and two terminal atoms.
Lone pairs of electrons occupy more space than bonding pairs of
electrons
9.5 Electronegativity and Polarity
Recall: Electronegativity is the ability of an atom to attract an electron.
Chemical bonding is like “Tug-o-War”
Bond Type
Non-polar Covalent
Polar Covalent
Ionic
Electronegativity
Difference
0-0.4
0.5-2.0
>2.0
Molecular Polarity
Molecules are either polar or non-polar
Both polar and non-polar molecules may contain polar bonds. What determines whether
a molecule is polar or non-polar is the symmetry of the molecule
PolarBonds
Present
Symmetr Polar/
y
NonPolar
Examples
No
No
Non-Polar
NO2
No
Yes
Non-polar
SiH4
Yes
No
Polar
NH3
Yes
Yes
Non-polar
CO2
VSEPR shapes that can demonstrate symmetry are:
Linear
Trigonal Planar
Tetrahedral
Solubility
“Like Dissolves Like”
Polar compounds and ionic compounds generally dissolve in polar substances
Non-polar substances dissolve in non-polar substances
Properties of Covalent Compounds
Covalent bonds “within” a molecule are strong (Intra-molecular)
Covalent bonds “between” two molecules are relatively weak (Intermolecular)
• Many covalent compounds are liquids and gases at room temperature.
• Covalent compounds have low melting and boiling points
Covalent Network Solids
Hard, Brittle, Non-conductors of heat and electricity
Diamond
Quartz