Chapter 6: Chemical Bonding
Section 2: Covalent Bonding and
Molecular Compounds
Overview
• We will define molecule and molecular formula.
• We will explain the relationships between
potential energy, distance between approaching
atoms, bond length, and bond energy.
• We will state the octet rule.
• We will see how to write Lewis structures.
• We will explain why people use resonance
structures.
Molecule
• A neutral group of atoms that are held together by
covalent bonds.
• Molecular Compound – A chemical compound
whose simplest units are molecules.
• Chemical Formula – It indicates the number of
atoms by using atomic symbols and subscripts.
• Molecular Formula – Shows the types and
numbers of atoms in a single molecule.
• Diatomic Molecule – A molecule that has only two
atoms.
Forming Covalent Bonds
• Approaching electrons are attracted so there
is a decrease in potential energy.
• The nuclei also repel each other which
increases potential energy.
• See page 165, Figure 6-5
Covalent Bond Characteristics
• Bond Length – The distance between two
bonded atoms at their minimum potential
energy. AKA average distance between two
bonded atoms.
• Bond Energy – The energy required to
break a chemical bond or form neutral
isolated atoms.
Octet Rule
• Chemical compounds tend to form so that
each atom has an octet of electrons in its
highest energy level by gaining, losing, or
sharing electrons.
• Exceptions:
– Hydrogen and Helium only need two valence
electrons.
– Boron can have less than eight, others can have
more than eight.
Electron-Dot & Lewis Structures
• Electron Dot Notation – An atom’s atomic
symbol with only dots representing the
valence electrons.
• An unshared pair or lone pair is two
electrons that are not involved bonding.
• Lewis Structure – The electron dot notation
of a molecule showing bonds.
More Lewis Structures
• Structural Formula – It indicates the kind, number,
arrangement, and bond types, but not the unshared
pairs.
• Single Bond – A covalent bond with two electrons
being shared. (Single Line)
• Double Bond – A covalent bond with four
electrons being shared. (Two Lines)
• Triple Bond – A covalent bond with six electrons
being shared. (Three Lines)
• Multiple Bonds – A double or triple bond.
Resonance
• The bonding of molecules that cannot be
represented correctly by just one Lewis Structure.
• There is more than one way to assemble the same
number of elements the right way.
How do you make these?