Comparison of Ionic, Polar Covalent, and Nonpolar Covalent Bonds.
Polar Covalent Bonds; Acids and Bases
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Transcript of Polar Covalent Bonds; Acids and Bases
Polar Covalent Bonds;Acids and Bases
Bond Moments and Dipole Moments
Formal Charge
Resonance
Bronsted-Lowry Acid/Base
Lewis Acid/Base
Bonding Pattens for C, N, and Osp3 sp2 sp
C CC
C
N N N
O O
tetrahedral geometry trigonal planar linear
Quick Review
Common Cationic, Neutral and Anionic Forms
Pauling Electronegativity Scale
Electronegativity Trends Ability to Attract the Electrons in a Covalent Bond
Electrostatic Potential Map Cholormethane
Opposite polarity in CH3Li
Methanol
Dipole Moment () is sum of the Bond Moments
Nonpolar CompoundsBond Moments Cancel Out
NCl3 and BCl3
NClCl
Cl B
Cl
= 0
Cl Cl
N-Cl bond momentsdo not cancel N
sp3 sp2
pyramidal trigonal planar
Nitromethane has 2 Formal Charges
CH3NO2 C N
O
O
H
HH
Formal Charge = [Group #] - [# bonds] - [# non-bonding electrons]
N = 5-4-0 = +1
O = 6-1-6 = -1
Both Resonance Structures Contribute to the Actual Structure
CH3NO2
C N
O
O
H
H
HHH
H
N
O
O
C
2 Equivalent Resonance Structures
Dipole Moment reflects Both Resonance Structures
C N
O
O
H
H
HHH
H
N
O
O
C
Resonance Hybrid
C
H
HH
O
O
N
Curved Arrow Formalism Shows flow of electrons
C N
O
O
H
H
HHH
H
N
O
O
C
Arrows depict electron pairs moving
Resonance Rules
• Cannot break single (sigma) bonds
• Only electrons move, not atoms
3 possibilities:– Lone pair of e- to adjacent bond position
• Forms bond
bond to adjacent atom
bond to adjacent bond position
Resonance Stabilization of IonsPositve charge is “delocalized”
CH
HC
C
H
H
H
C
C
H
H
H
H
HC
H
HC
H
H
H
CC
resonance hybrid
Definitions of Acids/Bases
Arrhenius acid - forms H3O+ in H2O
Bronsted-Lowry acid - donates a H+ (proton)
Lewis acid - accepts an electron pair to form a new bond
Arrhenius base - forms OH - in H2O
Bronsted-Lowry base - accepts a H + (proton)
Lewis base - donates an electron pair to form a new bond
Dissociation in H2OArrhenius Acid forms H3O+
Bronsted-Lowry Acid donates a H+
Reaction Described with Arrows
H Cl + OHH O
H
HH+ Cl
Lewis Acids and Bases
B H B H
base acid complex
arrow always goes from the base to the acid always originate your arrow at the e- donor
Equilibrium Reactions
Measuring Acid StrengthKa
Acid Strength defined by pKa
HCl + H2O H3O + Cl
Keq = [H3O ][Cl ]
[HCl][H2O]
Ka = Keq[H2O] =[H3O ][Cl ]
[HCl]= 10
7
pKa = -log(Ka) = -7
Resonance in Acetate Anion
Resonance Stabilization
C C
O
OH
H
HH
pKa 4.7
+ NaHCO3 HH
H
C
O
OC
HH
H
C
O
OC
H2CO3 + Na
HH
H
C C
O
O
resonance hybrid
Na
The Effect of Resonance on pKa
Draw the Conjugate Acid and Base
CH3CH2CH2OH + H2SO4
Propanol is a Base
base acid+ HSO4
H
CH3CH2CH2OHH2SO4+CH3CH2CH2OH
Draw the Conjugate Acid and Base
CH3CH2CH2OH + Na NH2
Propanol is an Acid
CH3CH2CH2O + Na NH2H CH3CH2CH2O Na
+ NH3
acid base
c.a.
c.b.
Some Acid-Base Reactions
What if there are no acidic protons?
B
H
HH+ N
HH
H
Lewis BaseLewis Acid
e- pair acceptor e- pair donor
B N
H
HH
H
HH
acid-base complex
Lewis Base = NucleophileLewis Acid = Electrophile
Functional groups
Functional groups determine chemistry
What will most likely happen if I add Br2?
What will most likely happen if I add HCl?