Formal Charge

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Formal Charge
Formal charge is the difference between the
number of valence electrons in a free
(uncombined) atom and the number of electrons
assigned to that atom when bonded to other atoms
in a Lewis structure
EOS
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Formal Charge
Usually, the most plausible Lewis structure is
one with no formal charges
When formal charges are required, they should be
as small as possible and negative formal charges
should appear on the most electronegative atoms
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Resonance Delocalized Bonding
Resonance theory states that whenever a molecule
or ion can be represented by two or more
plausible Lewis structures that differ only in
the distribution of electrons, the true structure
is a composite, or hybrid, of them Resonance
structures
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Molecules that Dont Followthe Octet Rule
Molecules with an odd number of valence electrons
have at least one of them unpaired and are called
free radicals
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Molecules that Dont Followthe Octet Rule
Some molecules have incomplete octets. These are
usually compounds of Be, B, and Al, generally
have some unusual bonding characteristics, and
are often quite reactive
EOS
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Molecules that Dont Followthe Octet Rule
Some compounds have expanded valence shells,
which means that the central atom has more than
eight electrons around it
EOS
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Molecules that Dont Followthe Octet Rule
An expanded valence shell may also need to
accommodate lone-pair electrons as well as
bonding pairs
EOS
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Bond Lengths
Bond order indicates whether a covalent bond is
single (b.o. 1), double (b.o. 2), or triple
(b.o. 3)
BondFormation
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Bond Energies (BE)
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Lewis Structure and Hydrocarbons
Hydrocarbons with double or triple bonds between
carbon atoms are called unsaturated hydrocarbons
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Lewis Structure and Hydrocarbons
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Polymers
Polymers are compounds in which many identical
molecules have been joined together
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Summary of Concepts

• Lewis symbols of main-group elements are related
  to their location in the periodic table
• The net energy decrease in the formation of an
  ionic crystal from its gaseous ions is the
  lattice energy
• A covalent bond forms by the sharing of an
  electron pair between atoms

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Summary of Concepts

• Electronegativity values are related to positions
  of the elements in the periodic table
• In some covalent bonds, one atom appears to
  provide both electrons in the bonding pair the
  bond is coordinate covalent
• Writing plausible Lewis structures for molecules
  or polyatomic ions involves writing the skeletal
  structure and distributing the valence electrons
  appropriately