November 16, 2009
•C h a p t e r 8
•Second
set of Chapt. 8 homework dates extended
until after break
•Lab Notes
•Today’s Topic:
Bond Properties (Sec. 8.4- there is no 8.3!)
Electron Distribution in Molecules (8.5)
What can we do with Lewis Structures?
 Bond Properties
1.
Polarity
2.
Bond Order
3.
Bond Length
4.
Bond Energy
RememberIt ALWAYS takes energy
to break a bond!
Making bonds releases
energy.
Bond Energy= The energy required
to separate two bonded atoms
The phosphate bond
in ATP is not
“broken”, it is
hydrolyzed, a multifaceted process that
does result in a net
release of energy.
However, it involves
more than the simple
breaking of one bond.
It ALWAYS requires energy to
BREAK a bond!
Bond Energy in Ionic Compounds: Lattice Energy
Energy to separate all the ions
NaCl(s)  Na+(g) + Cl-(g)
H = Lattice E = -790 kJ/mol
Lattice Energy
 Lattice energy = the energy it takes to pull ions in a
solid apart
Remember Coulomb’s Law!
 Depends on ion SIZE
 Depends on ion CHARGE

Which has the strongest lattice energy?
1. MgCl
2. BaCl
38%
30%
3. KCl
4. CsCl
21%
12%
1
2
3
4
Internal Properties of Molecules
 Resonance
 Formal Charge
 Oxidation Number
 Partial Charge
Resonance Structures
 A resonance structure is when more than one
arrangement of electrons is possible (i.e., there is
more than one reasonable Lewis structure)
Resonance and Bond Order
 Bond order will not equal the # of bonds if there is
more than one possible structure
 What is the bond order of the C-O bond in the
carbonate ion?
What is the bond order in SO2?
1. 1
49%
2. 1.25
3. 1.33
4. 1.5
5. 1.67
17%
6. 2.0
6%
6%
1
2.
16%
5%
3.
4.
5.
6.