Chapter 12
Chemical Bonding
Chemical Bond
• A bond is an
electrostatic force
of attraction
holding two atoms
together.
• Electrostatic
forces can be
either attractive or
repulsive (opposite
charges attract
whereas like
“Perhaps you gentlemen can tell me
charges repel).
what it is that you find so attractive”.
Chemical Bond
• Bonds are formed by valence electrons.
• The type of bond that forms between
atoms is based on what is occurring with
the valence electrons.
Ionic Bond
• Ionic bonds are formed when electrons are
transferred (lost and gained). Ionic bonds tend to
occur when a metal bonds with a nonmetal.
Covalent Bond
• Covalent bonds are formed when electrons are
shared. Covalent bonds tend to occur when a
nonmetal bonds with another nonmetal.
Polar Covalent and Nonpolar Covalent
• Covalent bonds can be nonpolar covalent which
result when electrons are shared equally between
atoms or polar covalent when electrons are shared
unequally between atoms.
Polar Covalent Bond
A
a
Metallic Bond
• Metallic bonds occur when valence electrons drift from one
metal atom to another. These “delocalized” electrons
therefore do not belong to any particular metal atom but instead
can be thought of as belonging to all the metal atoms.
Delocalized Electrons
Delocalized Electrons
• The delocalized electrons are what give
metals some of their unique properties
such as malleability, conductivity and
luster.
• The more delocalized electrons a metal
has the more enhanced these metallic
properties are.
Malleable vs. Brittle
Does the environment of the substance change?
Metallic: Metal ions in
a sea of delocalized
electrons
Ionic: Ions surrounded
by oppositely charged
ions.
Metals are malleable
Ionic compounds are brittle
Conductivity of Metals
4 Types of
Bonds
Electronegativity
• Electronegativity is the tendency of an
atom to attract electrons to itself when it is
bonded to another atom.
• It takes into account some of the concepts
that we discussed in earlier sections such
as atomic size, ionization energy, electron
arrangement, etc.
• It can also be used to determine bond type.
Electronegativity Table
Bond Polarity
• Most bonds are
a blend of ionic
and covalent
characteristics.
• Difference in
electronegativity
determines bond
type.
Electronegativity Difference
Electronegativity
Difference
Less than or equal to
0.3
Greater than 0.3 but
less than or equal to
1.7
Greater than 1.7
Examples:
Electrons are
primarily:
shared equally
Type of Bond
nonpolar covalent
shared unequally
polar covalent
transferred
ionic
HCl 2.83 – 2.20 = 0.63 ( polar covalent)
MgO 3.50 – 1.23 = 2.27 (ionic)
H2 = 2.20 –2.20 = (nonpolar covalent)
Electronegativity Difference
• The difference in electronegativity can also be used to
predict bond strength. The greater the difference in
electronegativity the stronger the bond.
• Examples:
HCl 2.83 – 2.20 = 0.63
MgO 3.50 – 1.23 = 2.27
H2 = 2.20 –2.20 = 0
Mg – O is the strongest bond and H – H is the weakest
Properties of Polar Covalent
bonds
• Form molecules
• Unequal sharing of electrons
• One atom has a stronger pull on the
electrons than the other atom does.
• Intermediate strength between ionic are
nonpolar covalent bonds.
• 88% of all bonds are polar covalent (Ionic
bonds make up about 10% of all bonds)
Bond Polarity
• Polar Covalent Bond
– e- are shared unequally
– nonsymmetrical e- density
– results in partial charges (dipole)
+


Properties of Non-Polar Bonds
•
•
•
•
Equal sharing of electrons
Weakest bond type
About 2% of all bonds are nonpolar covalent.
Usually identical atoms or nonmetals very
close on periodic table.
Bond Polarity
Ionic
Polar
Nonpolar
Homework
• Chapter 12 Homework Worksheet (9 questions).