Chapter 8
Bonding
Lewis Structures
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Diagram that shows
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American chemist Gilbert N. Lewis
Dots =
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Paired dots =
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Simple way of showing electrons
Most reactions involve only
Lewis Structures
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When drawing:
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Use electron configuration
Move in clockwise direction…
“12” = s orbital
“3, 6, 9” = p orbitals – fill each with ONE electron
before filling with pairs…
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Just like orbital filling diagram…
Examples: draw Lewis Structures of B, N, F, Ne
The Ionic Bond
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Ionic bond:
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Transfer of electrons from
Ions form with
Attraction between electrostatic charges is a
strong force
which holds
atoms together
The Ionic Bond
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NOT A
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Bond not just between
(for example) one
sodium and one
chloride
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The Ionic Bond
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Typically
Metals usually
Nonmetals usually
Predicting Formulas of Ionic
Compounds
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In almost all stable chemical compounds
of representative elements, each atom
attains a
This concept forms the basis for our
understanding of chemical bonding.
Predicting Formulas of Ionic
Compounds
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How many electrons must be gained or
lost to achieve noble gas configuration?
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Ba must lose
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S must gain
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Forms the ion
Forms the ion
So…must be ratio of
Predicting Formulas of Ionic
Compounds
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Elements in a family usually form
compounds with the same atomic ratios
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Because they have the same number of
valence electrons
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Must gain or lose the same number of electrons
See table 11.4 pg 233
Predicting Formulas of Ionic
Compounds
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The formula for sodium oxide is Na2O.
Predict the formula for
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Sodium sulfide
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Predicting Formulas of Ionic
Compounds
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Rubidium Oxide
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Rubidium
Oxygen
So…formula must be
This makes sense b/c rubidium is in same
family as sodium
The Covalent Bond
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A pair of
Most common type of bond
Stronger than
Electron orbital expands to include both nuclei
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most often found
between
Negative charges
allow positive nuclei
to be drawn close
to each other
The Covalent Bond
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Atoms may share more than one pair of
electrons
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Double bond –
Triple bond –
Multiple bonds are
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Covalent bonding between identical atoms
means electrons are shared
Covalent bonding between different atoms leads
to
Electronegativity
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The attractive force that an atom of an
element has for
Atoms have different electronegativities
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Electrons will spend more time near atom
with
So…one atom assumes a partial
 The other assumes a partial
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Electronegativity
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Electronegativity trends and periodic table
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See table 11.5 page 237
Generally increases from
Decreases
Highest is
Lowest is
Electronegativity
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Polarity is determined by difference in
electronegativity
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Nonpolar covalent
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Polar covalent
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Ionic compound
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Electronegativity
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If the electronegativity difference is
greater than
Above
Below
Electronegativity
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Polar bonds form between two atoms
Molecules can also be polar or nonpolar
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Dipole
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Polar
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Nonpolar
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Lewis Structures of Compounds
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Convenient way of showing ionic or
covalent bonds
Usually the single atom in a formula is the
central atom
The Ionic Bond
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LEWIS STRUCTURES of ionic bonds
The Covalent Bond
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LEWIS STRUCTURES of covalent bonds
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Use dashes instead of dots…
The Covalent Bond
Lewis Structures of Compounds
1)
Obtain the total number of valence
electrons
1)
2)
Add the valance electrons of all atoms
Ionic – add one electron for each negative
charge and subtract one electron for each
positive charge
Lewis Structures of Compounds
2)
3)
Write the skeletal arrangement of the
atoms and connect with a single covalent
vond
Subtract two electrons for each single
bond
1)
This gives you the net number of electrons
available for completing the structure
Lewis Structures of Compounds
4)
5)
Distribute pairs of electrons around each
atom to give each atom a noble gas
structure
If there are not enough electrons then
try to form double and triple bonds
Lewis Structures of Compounds
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Write the Lewis Structure for methane
CH4
Lewis Structures of Compounds
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Carbon Dioxide, CO2
Complex Lewis Structures
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Some molecules and polyatomic ions have
strange behaviors…
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No single Lewis structure is consistent
If multiple structures are possible the
molecule shows
Complex Lewis Structures
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Carbonate ion, CO32-
Compounds Containing
Polyatomic Ions
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Polyatomic ion:
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Behaves as a single unit in many chemical
reactions
Sodium carbonate (Na2CO3)
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