Chapter 6
Chemical Bonding Section 6.1: Introduction to Chemical Bonding
Things That You Should Know •  What is a chemical bond?
•  Why do atoms form chemical bonds?
•  What is the difference between ionic and
covalent bonding?
•  Why are most chemical bonds neither purely ionic
nor purely covalent?
•  How can you determine the type of bonding that
will result between any 2 elements?
Why Bond? •  Atoms rarely exist singly; instead, they exist in
combinations with other atoms held together by
chemical bonds.
•  Chemical bonds are mutual, electrical attractions
between the nuclei and valence electrons of different
atoms that bind the atoms together.
•  As independent particles, atoms have relatively high
potential energy. However, nature prefers more
stable arrangements.
•  Chemical bonds provide the atoms a low energy (more
stable) arrangement.
Types of Bonding •  There are 3 main types of bonding between
atoms.
•  Ionic
•  Covalent
•  Metallic
•  When atoms bond, their valence electrons are
redistributed. This redistribution determines
which type of bond will result.
Types of Bonding (cont’d) •  Ionic bonding results from
electrical attraction between
cations (+ ions) and anions (ions).
•  Covalent bonding results from
the sharing of valence electrons
between atoms.
Ionic or Covalent??? •  Purely ionic or purely covalent bonds are
extremely rare due to the attractive forces
between atoms and electrons.
•  By using the attractiveness of atoms to
electrons (electronegativity), we can determine
whether a bond is ionic or covalent.
•  In particular, if we use the two elements’
electronegativities, we can predict bond type.
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Ionic or Covalent??? (cont’d) •  In order to predict bond type,
we need a table of
electronegativities. [Refer to
Figure 5.20 on page 151 for
such a table!]
•  Guidelines to Know!!
•  0.0 – 0.3 = Non-polar covalent
•  0.3 – 1.7 = Polar covalent
•  1.7 – 3.3 = Ionic
Non-polar vs. Polar •  In order for a bond to be classified as either
non-polar or polar, we must look at the
sharing of the valence electrons.
•  If there is an unequal sharing of electrons,
the bond will be polar. As a result, a partial
positive charge and partial negative charge
will develop on the molecule.
•  If there is an equal sharing of electrons,
the bond will be non-polar. In this instance,
the atoms are either the same or are very
similar.
What’s the Difference? •  Classify the type of bonding that will result between the
following pairs of elements.
•  Sulfur and hydrogen
•  Chlorine and calcium
•  Sodium and iodine
•  Hydrogen and fluorine
•  Cesium and chlorine
•  Oxygen and fluorine
Section 6.2: Covalent Bonding and Molecular
Compounds
Things You Should Know •  What is a molecule?
•  What is a molecular formula?
•  What are the relationships between potential
energy, distance between approaching atoms,
bond length, and bond energy?
•  What is the octet rule?
•  What are the 6 basic steps used to write Lewis
structures?
Molecules, Molecules, Molecules •  Many compounds that surround us and that we
encounter exist in molecular form.
•  Molecules are neutral groups of atoms that are held in
place by covalent bonds.
•  Molecules can be composed of either only one type of
atom or more than one type.
•  We use chemical formulas to tell what types and
numbers of atoms are in compounds.
•  Molecular formulas tell how many atoms and what
type of atom are in a molecular compound.
Formation of a Covalent Bond Formation of a Covalent Bond (cont’d) The Octet Rule When two atoms form a covalent bond,
their shared electrons form
overlapping orbitals.
This achieves a noble-gas
configuration.
The bonding of two hydrogen atoms
allows each atom to have the stable
electron configuration of helium, 1s2.
The Octet Rule (cont’d) •  Noble gas atoms are unreactive because their electron
configurations are especially stable.
–  This stability results from the fact that the noble-gas atoms’
outer s and p orbitals are completely filled by a total of eight
electrons.
•  Other atoms can fill their outermost s and p orbitals by sharing
electrons through covalent bonding.
•  Such bond formation follows the OCTET RULE: Chemical compounds
tend to form so that each atom, by gaining, losing, or sharing
electrons, has an octet of electrons in its highest energy level.
Are there any exceptions? •  Exceptions to the octet rule include those for atoms that cannot fit
eight electrons, and for those that can fit more than eight electrons,
into their outermost orbital.
–  Hydrogen forms bonds in which it is surrounded by only two
electrons.
–  Boron has just three valence electrons, so it tends to form bonds in
which it is surrounded by six electrons.
–  Main-group elements in Periods 3 and up can form bonds with
expanded valence, involving more than eight electrons.