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Formal Charge
|
FC = (group #) - (loan pairs + bonds)
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|
Bond Enthalpy
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ΔHrxn = (sum of bonds broken) - (sum of bonds formed)
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|
Weaker bonds broken provide more exothermic reactions. Weaker product bonds make for a less exothermic reaction.
|
|
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Bond Order and Length
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Shorter bond length = greater bond order
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|
Single bonds are the longest and the weakest
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|
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Triple bonds are the shortest and the strongest
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|
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Non-integer bond order indicates resonance
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|
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Non-polar covalent bonds
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ex: Cl-Cl
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|
small energy difference in electronegativity
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|
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Polar Covalent Bonds
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ex: H-Cl
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|
medium energy difference
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|
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Ionic Bonds
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ex: Li-Cl
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|
large energy difference (over 1.7)
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|
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Average Bond Order
|
ABO = (# of bonds in the molecule) ÷ (# of resonance structures)
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Bond Order
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(bonds-antibonds) ÷ 2
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Bonds
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σ, π
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|
Anti-Bonds
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σ, π
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Sigma Bond
|
hybridized \
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|
Pi Bond
|
unhybridized p orbital \
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Loan Pair
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Spin Paired \ --> X
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|
Number of Electrons
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Electron Geometry
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Atoms + Loan Pairs
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Molecular Geometry
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|
2
|
linear
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2+0
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linear
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3
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trigonal planar
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3+0
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trigonal planar
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2+1
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bent
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||
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4
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tetrahedral
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4+0
|
tetrahedral
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3+1
|
trigonal pyramidal
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||
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2+2
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bent
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||
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5
|
trigonal bipyramidal
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5+0
|
trigonal bipyramidal
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4+1
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see-saw
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||
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3+2
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T-shaped
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||
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2+3
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linear
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||
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6
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octahedral
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6+0
|
octahedral
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|
5+1
|
square pyramidal
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||
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4+2
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square planar
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Requirements for a Polar Molecule
|
Bonds must be polar
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The molecule cannot have symmetry
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|
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A bond is polar if one side is more electronegative than the other
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Sublimation
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Na (s) + 1/2 Cl2 (g) --> Na (g) + Cl (g)
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+107.32 kJ
|
|
Cl-Cl bond energy
|
Na (g) + Cl (g) --> Na (g) + 1/2 Cl2 (g)
|
+121.68 kJ
|
|
ionization energy of sodium
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Na (g) + 1/2 Cl2 (g) --> Na+(g) + Cl (g) + e-
|
+496 kJ
|
|
Electron Affinity of Cl
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Na+(g) + Cl (g) + e- --> Na+ (g) + Cl- (g)
|
-349 kJ
|
|
Lattice Energy of NaCl
|
Na+ (g) + Cl- (g) --> NaCl (s)
|
-786 kJ
|
|
Valence Bond Theory
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When two atoms are in close proximity to one another, they arrange themselves at the lowest possible energy
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|
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Sigma bonds
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Formed by end-on overlap of orbitals along the internuclear axis
|
|
|
the electron density is highest right between the two atoms
|
||
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Pi bonds
|
Formed by side on overlap of orbitals
|
|
|
there is no electron density between the atoms
|
||
|
Weaker than sigma bonds
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||
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Valence electron pairs
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Electron Geometry
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Hybridization
|
|
2
|
linear
|
sp
|
|
3
|
trigonal planar
|
sp2
|
|
4
|
tetrahedral
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sp3
|
|
5
|
trigonal bipyramidal
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sp4
|
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6
|
octahedral
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sp5
|
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Single Bonds
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one sigma bond
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|
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Double Bonds
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one sigma, one pi bond
|
|
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Triple Bonds
|
one sigma, two pi bonds
|
|
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