Covalent Bonding
Chapter 6, Section 2
How does a covalent bond form?
How does a covalent bond form?
There is a balance between the attraction of
oppositely charged particles & the repulsion of
like charged particles
– FYI – bond length is the distance btwn atoms
A bond is formed when . . .
a distance between the nuclei is reached
in which
– repulsion and attraction forces are equal
– potential energy is at the lowest point possible
– at the bottom of the curve on PE graph
Energy in Bonds
When atoms form bonds, they become
more stable and release energy
That same amount of energy must be
absorbed to break the bond (ie. bond
energy)
The higher the bond energy, the stronger
the bond
Bond Energies
Do you see a trend between bond length
and bond energy?
Octet Rule
The ultimate goal of the atoms in a
compound is to look like a noble gas
Each atom will gain, lose, or share
electrons so that they have 8 electrons in
their outer energy level
Check out examples on p. 169
Exceptions to Octet Rule
Hydrogen is happy with 2 electrons
Boron can be happy with 6 electrons
Sulfur & phosphorus can actually get
MORE than 8 electrons (more on that
later)
e- dot diagrams
Shows the number of
valence electrons on
an s- or p-block
element
Draw dots around
element symbol to
match number of
valence electrons
Lewis Structures
e- dot diagrams for
compounds
– Dots show unshared
electrons
– Dashes show shared
electrons
So how do you draw a Lewis
structure?
1)
2)
3)
4)
5)
6)
7)
Determine the type & # of atoms in a molecule
Determine the number of valence e- on each atom
Add up total # of valence eArrange the atoms with the first element in the middle
and other elements radiating off. If carbon is present it
automatically goes in the middle
Connect the elements with dashes
Subtract shared electrons from total electrons
Distribute remaining electrons as unshared pairs first
to outer elements (follow the octet rule) and then to
center element.
WOW!!!
That last slide had a LOT of
words!!!
Let’s draw a Lewis Structure!
Draw the Lewis Structure for CH3Cl
duet
That’s all for now . . .
We will finish up the rest of section 2 next
class! 
Homework: p. 197 #38 & 39
November 1, 2010
Get out your homework and show it to me.
We will grade it as soon as the bell rings.
We will finish section 2 notes after grading.
There are a few different types of
covalent bonds . . .
Single covalent bond = 2 e- are shared
– Weakest & longest
– Ex. H2
Double covalent bond = 4 e- are shared
– Stronger & shorter
– Ex. O2, CO2
Triple covalent bond = 6 e- are shared
– Strongest & shortest
– Ex. N2, C2H2
Multiple Bonds Example
What is the Lewis structure for silicon
dioxide?
Multiple Bonds Example 2
What is the Lewis structure for
hydrocyanic acid (HCN)?
Polyatomic Ion Lewis Structures
Follow the same steps for drawing a
normal Lewis structure with the following
changes:
– If the polyatomic ion is negative, add the
charge to the total number of valence e– If the polyatomic ion is positive, subtract the
charge from the total number of valence e– Draw brackets around the entire diagram with
the charge written as a superscript
Polyatomic Ions
Example: CN-
NH4+ : ammonium ion
Polyatomic Ion Example
What is the Lewis structure for sulfate (SO42-)?
Polyatomic Ion Example
What is the Lewis structure for hydroxide (OH-)?
Another example
Draw the Lewis structure for ozone (O3).
ooooooo . . .resonance structures
Sometimes, molecular compounds can’t
make up their minds how they want to be
– One Lewis structure just is not enough
In these situations, 2+ Lewis structures are
drawn and the molecule actually is an
average of all of them
Ex. Ozone (O3)
Covalent Network Bonding
a different type of covalent bonding that is
more like ionic bonding
lots of nonmetal atoms covalently bonded
together in a network that looks like a
crystal
example:
– diamond
– silicon dioxide
– graphite