Chapter 8
Covalent Bonding
Honors Chemistry
Section 8.1 The Covelent Bond
Why do atoms bond?
• Atoms in non-ionic compounds share
electrons.
• The chemical bond that results from
sharing electrons is a covalent bond.
• A molecule is formed when two or
more atoms bond.
Ex: Hydrogen Molecule
H2
Diatomic molecules (H2, F2 for example)
exist because two-atom molecules are more
stable than single atoms.
There are 7 Diatomic molecules: H2 , N2 ,
O2 , F2 , Cl2 , Br2 , and I2 .
Types of Covalent Bonds:
• Single – 1 shared pair
• Double – 2 shared pair
• Triple - 3 shared pair
Section 8.2 Naming Molecules
Naming Binary Molecular Compounds
• The first element is always named first using the
entire element name.
• The second element is named using its root and
adding the suffix –ide.
• Prefixes are used to indicate the number of
atoms of each element in a compound.
You must remember these prefixes!!!
Naming Acids
An acid is a substance that donates H+ when in
solution.
There are two types of acids – binary and
oxyacids.
All binary acids have H+ combined with one other
nonmetal.
Naming Binary Acids
• The first word has the prefix hydro- followed by
the root of the element plus the suffix –ic.
• The second word is always acid
Ex: Hydrochloric acid is HCl
Naming Oxyacids
• An oxyacid is an acid that contains both a H+
and an oxyanion.
• Identify the oxyanion present.
• If the oxyanion ends in –ate, change -ate to -ic.
• If the oxyanion ends in –ite, change -ite to -ous.
Some molecular compounds are more
known by their common names.
Naming Molecular Compounds
Section 8.3 Molecular Structures
There are numerous ways to represent molecules:
Drawing Lewis Structures
– Predict the location of certain atoms.
– Determine the number of electrons available for
bonding.
– Determine the number of bonding pairs.
– Place the bonding pairs.
– Determine the number of non-bonding pairs
remaining.
– Determine whether the central atom satisfies the
octet rule.
Atoms within a polyatomic ion are
covalently bonded.
A coordinate covalent bond forms when one
atom donates both of the electrons to be shared
with an atom or ion that needs two electrons.
Ex: Chloric Acid, HClO3
Resonance Structures
Resonance is a
condition that occurs
when more than one
valid Lewis structure
can be written for a
molecule or ion.
Ex: This figure shows
three correct ways to
draw the structure for
nitrate, NO31-.
• Two or more correct Lewis structures that
represent a single ion or molecule are
resonance structures.
• The molecule behaves as though it has only one
structure.
Exceptions to the Octet Rule
Some molecules do not obey the octet rule!
1. Incomplete Octet - a small group of molecules
might have an odd number of valence electrons.
2. Suboctet - a few compounds form stable
configurations with less than 8 electrons around
the atom.
3. Expanded Octet - atoms with more than eight
valence electrons. (Forms with elements in
period 3 or higher with d-orbitals and can form
more than 4 covalent bonds)
Assigning Formal Charges
Formal Charges
• For each atom, count the electrons in lone pairs and
half the electrons it shares with other atoms.
• Subtract that from the number of valence electrons
from that atom: the difference is its formal charge.
The BEST Lewis structure…
• …is the one with the fewest charges.
• …puts a negative charge on the most
electronegative atom.
Section 8.4 Molecular Shapes
VSEPR Model
• The shape of a molecule determines many of its
physical and chemical properties.
• Molecular geometry (shape) can be determined
with the Valence Shell Electron Pair Repulsion
model, or VSEPR model which minimizes the
repulsion of shared and unshared atoms around
the central atom.
VSEPR Model
The central
atom in this
molecule, A, has
four electron
domains.
• We can refer to the
electron pairs as
electron domains.
• In a double or triple
bond, all electrons
shared between those
two atoms are on the
same side of the central
atom; therefore, they
count as one electron
domain.
VSEPR Model - Electron Domain
Geometry
These are the
electron-domain
geometries for two
through six
electron domains
around a central
atom.
VSEPR Model (cont.)
• Electron pairs repel each other and cause
molecules to be in fixed positions relative to
each other.
• Unshared electron pairs also determine the
shape of a molecule.
• Electron pairs are located in a molecule as far
apart as they can be.
VSEPR Model (cont.)
VSEPR Model (cont.)
VSEPR Model (cont.)
VSEPR Model (cont.)
VSEPR Model (cont.)
Hybridization is a
process in which
atomic orbitals mix
and form new,
identical hybrid
orbitals.
Once you know the
electron-domain
geometry, you know
the hybridization state
of the atom.
Section 8.5 Electronegativity and
Polarity
Electronegativity and Bond Character
• Electronegativity measures the attraction for a shared
pair of electrons in bonded atoms.
Why aren’t values for the Noble Gases given???
EN Difference & Bond Character…
Polar Covalent Bonding
• Unequal sharing of electrons results in a polar covalent
bond.
• Bonding is often not clearly ionic or covalent.
• Polar Covalent Bonding in a Water Molecule
• Covalently bonded molecules are either polar or nonpolar.
• Non-polar molecules are not attracted by an electric
field, whereas polar molecules will always align with an
electric field.
• H2O and CCl4 both contain polar covalent bonds
between atoms, but only one of these molecules is a
polar covalent molecule. How can you tell?
Polar Covalent Bonds (cont.)
• Solubility is the property of a substance’s ability
to dissolve in another substance.
• Polar molecules and ionic substances are
usually soluble in polar substances.
• Non-polar molecules dissolve only in non-polar
substances.
• LIKE DISSOLVES LIKE!!!!!
Properties of Covalent Compounds
Many physical properties are due to intermolecular
forces.
• Low melting and boiling points of molecular
substances.
• Relatively soft solids.
• Molecules can align in a crystal lattice, similar to
ionic solids but with less attraction between
particles.
Properties of Covalent Compounds
Solids composed of only atoms interconnected by
a network of covalent bonds are called covalent
network solids.
• Quartz and diamonds are two common examples of
network solids.