1 1.2 Ionic bonding Electrons Transferred Big differences in E.N. - - PDF document

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Mar 10, 2024 470 likes •676 views

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

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1 1.3 Covalent Bonding ‐ Electrons Shared

1.2-1.3 Bonding

1.2 Ionic Bonding ‐ Electrons Transferred

type of bond that is formed is dictated by the relative electronegativities of the elements involved Atoms trying to attain the stable configuration of a noble (inert) gas ‐ often referred to as the octet rule

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the attraction of an atom for electrons

Electronegativity

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1.2 Ionic bonding Electrons Transferred

 Big differences in E.N. values;  Metals reacting with non‐metals

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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

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1.3 Lewis Dot Structures of Molecules

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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

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1.5 Polar covalent bonds and electronegativity

H2 HF H2O CH4 CH3Cl Based on electronegativity differences

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1.6 Structural Formula - Shorthand in Organic Chemistry

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1.6 Constitutional Isomers

Same molecular formula, completely different chemical and physical properties

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1.7 Formal Charge group number ‐ number of bonds ‐ number of unshared electrons Formal charge

O N O O H

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1.8 Resonance Structures - Electron Delocalization

Table 1.6 – formal rules for resonance

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1.9 Shapes of Molecules Shapes of molecules are predicted using VSEPR theory

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1.9 Shape of a molecule in terms of its atoms

Table 1.7 – VSEPR and molecular geometry

Figure 1.9

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Table 1.7 VSEPR & Molecular Geometry

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Trigonal planar geometry of bonds to carbon in H2C=O

Linear geometry of carbon dioxide

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1.10 Molecular dipole moments

Figure 1.7

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1.11 Curved Arrows – Extremely Important

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Many reactions involve both bond breaking and bond formation. More than one arrow may be required. Curved Arrows to Describe a Reaction

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Many reactions involve both bond breaking and bond formation. More than one arrow may be required. Curved Arrows to Describe a Reaction

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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.

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1.13 A Brønsted-Lowry Acid-Base Reaction

A proton is transferred from the acid to the base

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1.13 A Brønsted-Lowry Acid-Base Reaction

Definitions to describe species on each side of equation

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1.13 A Brønsted-Lowry Acid-Base Reaction

Curved arrows describe how bonds are formed and broken

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Proton Transfer from HBr to Water

Hydronium ion

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Proton Transfer from HBr to Water

Hydronium ion

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Proton Transfer from HBr to Water

Hydronium ion

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Equilibrium Constants for Chemical Reactions

G = H – TS G = ‐ RTlnK

Reactants Products

Equilibrium Constant (K) = [Products] [Reactants]

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Equilibrium Constants for Chemical Reactions

G = ‐ RTlnK Equilibrium Constant (K) = [Right‐Side] [Left‐Side]

Left-Side Right-Side

K > 1, RHS favoured; K ~ 1, equal; K < 1, LHS favoured

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Equilibrium Constant for Proton Transfer

Br H O + Br + H H O H H H [H3O+] [Br-] [HBr] Ka = pKa = - log10Ka

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Acids and Bases: Arrow Pushing

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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

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1.14 What happened to pKb?

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A separate “basicity constant” Kb is not necessary

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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 Not at all acidic Corresponding base Extremely strong

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1.15 How Structure Affects Acid/Base Strength

HF HF HCl HCl HBr HBr HI HI p pK Ka

3.1 3.1

3.9

5.8

10.4

10.4 weakest acid strongest acid strongest H—X bond weakest H—X bond

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Inductive Effects

Electronegative groups/atoms remote from the acidic H can effect the pKa

f the acid.

pKa = 16 pKa = 11.3

CH3CH2O H CF3CH2O H

 O – H bond in CF3CH2OH is more polarized by EWG  CF3CH2O‐ anion is stabilized by EW fluorine atoms YSU YSU

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). pKa ~16 pKa ~5

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1.16 Acid-Base Reactions - Equilibria

The equilibrium will lie to the side of the weaker conjugate base

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1.17 Lewis acids and Lewis bases

Product is a stable substance. It is a liquid with a boiling point of 126 °C. Of the two reactants, BF3 is a gas and CH3CH2OCH2CH3 has a boiling point of 34 °C.