SLIDE 1
1.2-1.3 Bonding Atoms trying to attain the stable configuration of a - - PowerPoint PPT Presentation
1.2-1.3 Bonding Atoms trying to attain the stable configuration of a - - PowerPoint PPT Presentation
1.2-1.3 Bonding Atoms trying to attain the stable configuration of a noble (inert) gas - often referred to as the octet rule 1.2 Ionic Bonding - Electrons Transferred 1.3 Covalent Bonding - Electrons Shared type of bond that is formed is dictated
SLIDE 2
SLIDE 3
1.2 Ionic bonding Electrons Transferred Big differences in E.N. values Metals reacting with non-metals
SLIDE 4
Important Electronegativity Values H 2.1 Li Be B C N O F 1.0 2.0 2.5 3.0 3.5 4.0 Cl 3.0 Br 2.8 I 2.5
SLIDE 5
1.3 Covalent Bonding - Similar electronegativities
H . + H . H : H
Hydrogen atoms Hydrogen molecule
C
+ 4 H C H H H H
Lewis dot representations of molecules
B.D.E +104 kcal/mol B.D.E +104 kcal/mol
B.D.E. = bond dissociation energy
SLIDE 6
1.3 Lewis Dot Structures of Molecules
SLIDE 7
1.4 Double bonds and triple bonds
H C C H H : C : : : C : H C : : C H H H H C C H H H H
Double bonds - alkenes Triple bonds - alkynes
SLIDE 8
1.5 Polar covalent bonds and electronegativity
H2 HF H2O CH4 CH3Cl
Based on electronegativity
Li Li H H δ δ− − δ δ+ + F F: : .. .. .. .. H H δ+ δ+ δ− δ−
SLIDE 9
1.6 Structural Formula - Shorthand in Organic Chemistry
CH3CH2CH2CH3 H H H H H H H H H H
CH3CH2CH2CH2OH OH
H Cl H H H H H H H H H H Cl
SLIDE 10
1.6 Constitutional Isomers
H C H H O C H H H H C C O H H H H H
Same molecular formula, completely different chemical and physical properties
SLIDE 11
1.7 Formal Charge Formal charge = group number
- number of bonds
- number of
unshared electrons
O N O O H
O O O
SLIDE 12
1.8 Resonance Structures - Electron Delocalization
O O O O O O CH3 C O O CH3 C O O
Table 1.6 – formal rules for resonance
SLIDE 13
1.9 Shapes of Molecules
Shapes of molecules are predicted using VSEPR theory
SLIDE 14
1.9 Shape of a molecule in terms of its atoms
Figure 1.9
Table 1.7 – VSEPR and molecular geometry
SLIDE 15
SLIDE 16
Trigonal planar geometry of bonds to carbon in H2C=O Linear geometry of carbon dioxide
SLIDE 17
1.10 Molecular dipole moments Figure 1.7
SLIDE 18
- Curved arrows are used to track the flow of
electrons in chemical reactions.
- Consider the reaction shown below which shows
the dissociation of AB: 1.11 Curved Arrows – Extremely Important
A B A+ + B-
SLIDE 19
Many reactions involve both bond breaking and bond formation. More than one arrow may be required. Curved Arrows to Describe a Reaction
H O + C H H H Br C H O H H H + Br-
SLIDE 20
1.12 Acids and Bases - Definitions Arrhenius An acid ionizes in water to give protons. A base ionizes in water to give hydroxide ions. Brønsted-Lowry An acid is a proton donor. A base is a proton acceptor. Lewis An acid is an electron pair acceptor. A base is an electron pair donor.
SLIDE 21
H A B . . B H A– . . + 1.13 A Brønsted-Lowry Acid-Base Reaction A proton is transferred from the acid to the base. + + base acid conjugate acid conjugate base
SLIDE 22
hydronium hydronium ion (H ion (H3
3O
O+
+)
) H H Br Br O O H H H H . . . . . . . . H H H H . . . . O O H H Br Br – – . . . . . . . . .. .. .. .. .. .. .. .. . . . . + + Proton Transfer from HBr to Water base base acid acid conjugate conjugate conjugate conjugate acid acid base base + + + +
SLIDE 23
[H3O+][Br–] [HBr] Ka = H Br O H H . . . . H H . . O H Br – . . . . .. .. .. .. . . + + + pKa = – log10 Ka Equilibrium Constant for Proton Transfer
SLIDE 24
H O H + H Br H O H + Br H ?
Acids and Bases: Arrow Pushing
H O H + H Br H O H + Br H H O H + H Br H O H + Br H
[H3O+][Br–] [HBr] Ka = ~ 106 for HBr, pKa = - 5.8
SLIDE 25
SLIDE 26
SLIDE 27
Need to know by next class:
pKa = -log10Ka STRONG ACID = LOW pKa WEAK ACID = HIGH pKa HI, HCl, HNO3, H3PO4 pKa -10 to -5 Super strong acids H3O+ pKa – 1.7 RCO2H pKa ~ 5 acids PhOH pKa ~ 10 get H2O, ROH pKa ~ 16 weaker RCCH (alkynes) pKa ~ 26 RNH2 pKa ~ 36 Extremely weak acid RCH3 pKa ~ 60 Not acidic at all
SLIDE 28
1.14 What happened to pKb?
- A separate “basicity constant” Kb is not necessary.
- Because of the conjugate relationships in the
Brønsted-Lowry approach, we can examine acid- base reactions by relying exclusively on pKa values.
C H H H H C H H H
pKa ~60 Essentially not acidic Corresponding base Extremely strong
SLIDE 29
1.15 How Structure Affects Acid/Base Strength
Bond Strength
- Acidity of HX increases (HI>HBr>HCl>HF) down the periodic table as
H-X bond strength decreases and conjugate base (X:- anion) size increases (basic strength of anion decreases).
strongest H—X bond weakest H—X bond
SLIDE 30
Electronegativity Acidity increases across periodic table as the atom attached to H gets more electronegative (HF>H2O>H2N>CH4).
least electronegative most electronegative
SLIDE 31
Inductive Effects Electronegative groups/atoms remote from the acidic H can effect the pKa of the acid.
pKa = 16 pKa = 11.3
CH3CH2O H CF3CH2O H
- O – H bond in CF3CH2OH is more polarized
- CF3CH2O- is stabilized by EW fluorine atoms
SLIDE 32
Resonance Stabilization in Anion Delocalization of charge in anion (resonance) makes the anion more stable and thus the conjugate acid more acidic e.g. (CH3CO2H > CH3CH2OH).
CH3 C O O CH3 C O O CH3 C OH O CH3 CH2 OH CH3 CH2 O
pKa ~16 pKa ~5
SLIDE 33
1.16 Acid-base reactions - equilibria
H Cl NaOH NaCl + H2O +
H3C O OH NaOH H3C O ONa H2O
+ +
H2O CH3ONa NaOH CH3OH
+ +
The equilibrium will lie to the side of the weaker conjugate base
SLIDE 34
1.17 Lewis acids and Lewis bases
F F3
3B
B + + O O CH CH2
2CH
CH3
3
CH CH2
2CH
CH3
3
- –
– + + F F3
3B
B O O CH CH2
2CH
CH3
3
CH CH2
2CH
CH3
3
- Lewis acid