Covalent Bonding
8.2 The Nature of Covalent Bonding
The Nora School
955 Sligo Avenue
Silver Spring, Maryland 20910
Chemistry
Period _______
Molecular Compound Review
• How are the melting points and boiling
points of molecular compounds usually
different from ionic compounds?
• What information does a molecular
formula provide?
• Give an example of a diatomic
molecule found in Earth’s atmosphere.
The Nora School
955 Sligo Avenue
Silver Spring, Maryland 20910
Chemistry
Period _______
The Octet Rule in Covalent
Bonding
• Recall that in forming ionic compounds,
electrons tend to be transferred so that
each ion acquires a noble gas
configuration.
• In forming covalent bonds, electron
sharing usually occurs so that atoms
attain the electron configuration of
noble gases.
The Nora School
955 Sligo Avenue
Silver Spring, Maryland 20910
Chemistry
Period _______
1
The Octet Rule in Covalent
Bonding
• Combinations of atoms of the
nonmetallic elements are likely to form
covalent bonds.
• In this case the atoms usually acquire a
total of eight electrons, or an octet.
• Therefore, the Octet rule applies to
covalent bonds too.
The Nora School
955 Sligo Avenue
Silver Spring, Maryland 20910
Chemistry
Period _______
Single Covalent Bonds
• Two atoms held together by sharing a pair of
electrons are joined by a single covalent
bond.
• An electron dot structure for a single
covalent bond is represented by two dots.
• A structural formula represents the
covalent bonds by dashes and shows
arrangement.
The Nora School
955 Sligo Avenue
Silver Spring, Maryland 20910
Chemistry
Period _______
Single Covalent Bonds
• A pair of valence electrons that is not
shared between atoms is called an
unshared pair, or lone/non-bounding
pair.
The Nora School
955 Sligo Avenue
Silver Spring, Maryland 20910
Chemistry
Period _______
2
Lets Practice
• Draw the electron dot structure and
structural formula for
– Ammonia (NH3)
– Methane (CH4)
– Hydrochloric Acid (HCl)
– Hydrogen Peroxide (H2O2)
– Phosphorus Chloride (PCl3)
The Nora School
Chemistry
955 Sligo Avenue
Silver Spring, Maryland 20910
Period _______
Double and Triple Covalent
Bonds
• Atoms form double or triple covalent
bonds if they can attain a noble gas
structure by sharing two pairs or three
pairs of electrons.
The Nora School
Chemistry
955 Sligo Avenue
Silver Spring, Maryland 20910
Period _______
Coordinate Covalent Bonds
• A coordinate covalent bond is a
covalent bond in which one atom
contributes both bonding electrons.
• The shared electron pair comes from
one of the bonding atoms.
The Nora School
955 Sligo Avenue
Silver Spring, Maryland 20910
Chemistry
Period _______
3
Bond Dissociation Energies
• When hydrogen atoms (H) form hydrogen
molecules (H2), a large amount of heat is
liberated. Indicator of stability.
• Bond Disassociation Energy is the
measure of energy needed to break apart a
covalent bond.
• For H2, the bond disassociation energy is
435 kJ/mol. (Bigger Stronger)
The Nora School
955 Sligo Avenue
Silver Spring, Maryland 20910
Chemistry
Period _______
Resonance
• Molecules which have more than one
configuration exists as hybrids, a mixtures of
both extreme resonance structures.
• A resonance structure is a structure that
occurs when it is possible to draw two or
more valid electron dot structures w/ the
same.
The Nora School
955 Sligo Avenue
Silver Spring, Maryland 20910
Chemistry
Period _______
Exceptions to the Octet Rule
• The octet rule cannot be satisfied in
molecules whose total number of
valence electrons is an odd number.
• There are also molecules in which an
atom has fewer, or more, than a
complete octet of valence electrons
The Nora School
955 Sligo Avenue
Silver Spring, Maryland 20910
Chemistry
Period _______
4
Exceptions to the Octet Rule
• Hydrogen, Beryllium and Boron have
two few valence electrons to ever
obtain a full octet.
• Elements in periods 3, 4, 5, 6 and 7 can
expand their octet to have 10, 12, or 14
valence electrons.
The Nora School
955 Sligo Avenue
Silver Spring, Maryland 20910
Chemistry
Period _______
5