The Nature of Covalent Bonding
8.2
Page 217
The Octet Rule in Covalent Bonding
• In forming covalent bonds, electron sharing
usually occurs so that atoms attain the
electron configurations of noble gases.
• A pair of hydrogen atoms share 2 electrons
giving the electron configuration of helium.
• Combinations of atoms of the nonmetallic
elements in Groups 4A, 5A, 6A, and 7A are
likely to form covalent bonds.
Single Covalent Bonds
• Two atoms held together by sharing a pair of
electrons are said to be joined by a single
covalent bond.
Single Covalent Bonds
• The pair of shared electrons
forming the covalent bond
is often represented as a
dash.
• A structural formula
represents the covalent
bonds by dashes and shows
the arrangement of
covalently bonded atoms.
• The molecular formula
indicates only the number
of hydrogen atoms in each
molecule
Single Bonds of the Halogens
• Halogens form single
covalent bonds in their
diatomic molecules.
• These atoms have seven
valence electrons,
needing only one
additional electron to
obtain the configuration
of a noble gas.
Single Covalent Bonds
• A pair of valence
electrons that is not
shared between atoms
is called an unshared
pair, also know as, a
lone pair or a
nonbonding pair.
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.
• Single, double, and triple covalent bonds also
exist between unlike atoms.
Coordinate Covalent Bonds
• In a coordinate covalent bond, the shared
electron pair comes from one of the bonding
atoms.
• One atom contributes both bonding electrons.
• Once formed, a coordinate covalent bond is
like any other covalent bond.
Polyatomic Ions
• Tightly bound group of atoms that has a
positive or negative charge and behaves as a
unit.
• Most polyatomic cations and anions contain
both covalent and coordinate covalent bonds.
• Therefore, compounds containing polyatomic
ions include both ionic and covalent bonding.
Polyatomic Ion
Bond Dissociation Energies
• The energy required to break the bond
between two covalently bonded atoms.
• Usually expressed as the energy needed to
break one mole of bonds.
• A large bond dissociation energy corresponds
to a strong covalent bond.
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.
– ClO2
– NO
– Read page 228-229