Chemical Bonding
Chapter 8 Sections 1 & 2
• A chemical bond is: a force of
attraction between any two atoms
in a compound.
• Bonding between atoms occurs
because it creates a more stable
arrangement for the atoms.
Lewis Symbols – Dot Diagrams
• Convenient way to show the valence
electrons
Three types of bonding
• Metallic bonding – results from the
attraction between metal atoms and the
surrounding sea of electrons
• Ionic bonding – results from the electrical
attraction between large numbers of
cations and anions
• Covalent bonding – results from the
sharing of electron pairs between two
atoms
Ionic Bonding
• Many atoms transfer electrons
and other atoms accept electrons,
creating cations (positive metal
ions) and anions (negative
nonmetal ions).
• The resulting ions are attracted to
each other by electrostatic
force.
Ionic bonding between Na and Cl
Sodium atom
1s2 2s2 2p6 3s1
Chlorine atom
1s2 2s2 2p6 3s2 3p5
1s2 2s2 2p6 3s1
1s2 2s2 2p6 3s2 3p5
Sodium ion Na1+
1s2 2s2 2p6
Chlorine ion Cl11s2 2s2 2p6 3s2 3p6
Covalent bonding
• In many cases electrons do
not completely transfer from
one atom to another.
• The electrons between atoms
are shared.
Covalent bonding between H2
• Hydrogen’s electron configuration is
1s1
• Because both H atoms need 1 more
electron to become isoelectronic with
He, it is unlikely that either will give up
an electron.
Covalent bonding between H2
↑
1s
↓
1s
They share the two electrons.
H· + H ·  H : H
Types of Covalent Bonds
• When electrons are shared equally
the bond is called a NONPOLAR
covalent bond. (i.e. H2)
• Sometimes the electrons between two
atoms are NOT shared equally. The
bond created is called a POLAR
covalent bond.
..
..
H· + ·Cl:
. .  H:Cl:
..
Polar Covalent Bonding
• An example of this would be HCl.
HCl molecule
Hydrogen atom
↑
1s
Chlorine atom
[Ne] ↑↓
3s
↑↓ ↑↓ ↓
3p
How to classify bond types
• Electronegativity – measure of the ability
of an atom to attract electrons in a
chemical bond
• Each element on the periodic table is
assigned an electronegativity value (see
page 353) that ranges from 0.7 to 4.0.
• The difference in the electronegativity
determines the bonding type (ionic, polar
covalent, or nonpolar covalent).
If the electronegativity difference is:
1.7 and higher
ionic
0.3 to 1.7
polar
covalent
0.0 to 0.3
nonpolar
covalent
What if I get an electronegativity
difference that is 0.3 or 1.7?
• These cut-off numbers are
guidelines.
• It is a gradual change not stair-step.
Ionic Character
• As the electronegativity difference
increases, the ionic character increases
as well!
Practice Problems
What type of bond will occur between
iodine and the following elements:
cesium, iron, and sulfur?
Bonding
between I and:
Cesium
Iron
Sulfur
Electronegativity
difference
Bond Type
Answers to problems
Bonding
between I and:
Electronegativity
difference
Bond Type
Cesium
2.5 – 0.7 = 1.8
Ionic
Iron
2.5 – 1.8 = 0.7
Polar
covalent
Sulfur
2.5 – 2.5 = 0.0
Nonpolar
covalent
Determine the type of bond
between the following pairs.
Bonding
between
Li & Cl
S & O
Ca & Br
P & H
Si & Cl
S & Br
Electronegativity
difference
Bond type
Answers
Bonding Electronegativity
between
difference
Li & Cl
3.0 – 1.0 = 2.0
Bond type
Ionic
S & O
3.5 – 2.5 = 1.0
Polar covalent
Ca & Br
2.8 – 1.0 = 1.8
Ionic
P & H
2.1 – 2.1 = 0.0
Nonpolar covalent
Si & Cl
3.0 – 1.8 = 1.2
Polar covalent
S & Br
2.8 – 2.5 = 0.3
Nonpolar covalent