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Hybridization and MO Theory Cheat Sheet by

chapters 7 and 8 CHEM200

Hybrid­ization

Formal Charge
FC = (group #) - (loan pairs + bonds)
Bond Enthalpy
ΔHrxn = (sum of bonds broken) - (sum of bonds formed)
 
Weaker bonds broken provide more exothermic reactions. Weaker product bonds make for a less exothermic reaction.
Bond Order and Length
Shorter bond length = greater bond order
 
Single bonds are the longest and the weakest
 
Triple bonds are the shortest and the strongest
 
Non-in­teger bond order indicates resonance
Non-polar covalent bonds
ex: Cl-Cl
 
small energy difference in electr­one­gat­ivity
Polar Covalent Bonds
ex: H-Cl
 
medium energy difference
Ionic Bonds
ex: Li-Cl
 
large energy difference (over 1.7)
Average Bond Order
ABO = (# of bonds in the molecule) ÷ (# of resonance struct­ures)

MO Theory

MO diagram for F2, O2, Ne2, and all other molecules

MO Theory

Bond Order
(bonds­-an­tib­onds) ÷ 2
Bonds
σ, π
Anti-Bonds
σ, π
Sigma Bond
hybridized \
Pi Bond
unhybr­idized p orbital \
Loan Pair
Spin Paired \ --> X
 

VSEPR

Number of Electrons
Electron Geometry
Atoms + Loan Pairs
Molecular Geometry
2
linear
2+0
linear
3
trigonal planar
3+0
trigonal planar
  
2+1
bent
4
tetrah­edral
4+0
tetrah­edral
  
3+1
trigonal pyramidal
  
2+2
bent
5
trigonal bipyra­midal
5+0
trigonal bipyra­midal
  
4+1
see-saw
  
3+2
T-shaped
  
2+3
linear
6
octahedral
6+0
octahedral
  
5+1
square pyramidal
  
4+2
square planar

Polarity

Requir­ements for a Polar Molecule
Bonds must be polar
 
The molecule cannot have symmetry
 
A bond is polar if one side is more electr­one­gative than the other

MO Theory

Diagram for B2, C2, and N2
 

The Born-Haber Cycle

Sublim­ation
Na (s) + 1/2 Cl2 (g) --> Na (g) + Cl (g)
+107.32 kJ
Cl-Cl bond energy
Na (g) + Cl (g) --> Na (g) + 1/2 Cl2 (g)
+121.68 kJ
ionization energy of sodium
Na (g) + 1/2 Cl2 (g) --> Na+(g) + Cl (g) + e-
+496 kJ
Electron Affinity of Cl
Na+(g) + Cl (g) + e- --> Na+ (g) + Cl- (g)
-349 kJ
Lattice Energy of NaCl
Na+ (g) + Cl- (g) --> NaCl (s)
-786 kJ

Sigma and Pi Bonds

Valence Bond Theory
When two atoms are in close proximity to one another, they arrange themselves at the lowest possible energy
Sigma bonds
Formed by end-on overlap of orbitals along the intern­uclear axis
 
the electron density is highest right between the two atoms
Pi bonds
Formed by side on overlap of orbitals
 
there is no electron density between the atoms
 
Weaker than sigma bonds
Valence electron pairs
Electron Geometry
Hybrid­ization
2
linear
sp
3
trigonal planar
sp2
4
tetrah­edral
sp3
5
trigonal bipyra­midal
sp4
6
octahedral
sp5
Single Bonds
one sigma bond
Double Bonds
one sigma, one pi bond
Triple Bonds
one sigma, two pi bonds

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