Chapters 1 & 2

MolecularRepresentations

General Chemistry ReviewElectronic Structure

and Bonding

Molecular Representations

Klein: 2.1, 2.2, 2.6

Molecular Representations

Empirical Formula, Molecular Formula, Structure: (Lewis, Kekule, Condensed, Line), Visual Model: wireframe, stick, ball & stick, space filling, electrostatic, energy surface

Draw bond-line structures for each of the four molecules.

1.

2.

3.

4.

ketone

O

1.

aldehyde

H

O

O

2.

NOT

carboxylic acid

C

O

O

H

C

O

2

H

O

H

O

or

or

3.

ester (carboxylic acid ester)

O

O

C

H

3

O

O

C

O

O

C

H

3

or

NOT

4.

Introduction to Organic Functions (Functional Groups)(Klein 2.3)

1.

2.

3.

4.

ketone

aldehyde

carboxylic acid

ester (carboxylic acid ester)

Worksheet 3: Organic Functional Groups (2 Sudoku)http://chemconnections.org/organic/chem226/226assign-12.html#Worksheets

Worksheet 4: Functions, Polarity, Formal Chargehttp://chemconnections.org/organic/chem226/226assign-12.html#Worksheets

Question 2.1

• The molecular formula of morpholine is:• A) C2HNO• B) C4HNO• C) C4H4NO• D) C4H5NO• E) C4H9NO

Question 2.2

• The respective number of bonded pairs of electrons and of unshared pairs of electrons in morpholine is:

• A) 7, 0• B) 7, 1• C) 15, 0• D) 15, 1• E) 15, 3

Formulas &Kekulé / Condensed / Bond-Line

Structures / Drawings

Molecular formula? Empirical Formula?

Bond-Line Structure?

C7H16O C7H16O

O

H

Question 2.3

• The bond-line representation for (CH3)2CHCH2CH2CHBrCH3 is

•• A) B)•

• C) D)

Select the best condensed structural formula for the following bond-line structure:

HHO OH

O

A. (CH3)2CHCH2COHOHCOHB. CH3CH3CHCH2C(OH)2CHOC. (CH3)2CHCH2C(OH)2CHOD. (CH3)2CHCH2C(OH)2COHE. CH3CHCH3CH2C(OH)2CHO

Question 2.4

Line Drawing and Ball & Stick

8.16 Å (0.816 nm)

http://chemconnections.org/COT/chemical-communication/ChemComm.html

Question 2.5While on-line, examine the jmol-structure on the left. Which one of the formulas or structural renderings that follow is correct?

C

H

3

C

H

2

O

H

C

H

2

C

O

O

H

C

H

3

O

O

H

O

H

O

C

2

H

3

O

B)

C)

D)

E)

A)

http://chemconnections.org/organic/chem226/Labs/VSEPR/acetic-acid.html

Worksheet 2: Structures, Formulas & Orbitalshttp://chemconnections.org/organic/chem226/226assign-12.html#Worksheets

Question 2.6

• How many constitutional alcohol isomers have the molecular formula C4H10O?

• A) two• B) three• C) four• D) five• E) sixSEE:http://m.wolframalpha.com/examples/Chemistry.html

More Molecular Representations

Empirical Formula, Molecular Formula, Structure: (Lewis, Kekule, Condensed, Line), Visual Model: wireframe, stick, ball & stick, space filling, electrostatic, energy surface

Worksheet: Organic Molecules 1http://chemconnections.org/COT/organic1/VSEPR/

Very Large Molecules:DNAhttp://www.umass.edu/microbio/chime/beta/pe_alpha/atlas/atlas.htm

Views & Algorithms

10.85 Å10.85 Å

Several formats are commonly used but all rely on plotting atoms in 3 dimensional space; .pdb is one of the most popular.

Very Large Moleculeshttp://info.bio.cmu.edu/courses/03231/ProtStruc/ProtStruc.htm

B-DNA: Size, Shape & Self Assembly

http://molvis.sdsc.edu/pdb/dna_b_form.pdb

46 Å

12 base sequence

(1953-2003)

Rosalind Franklin’sPhoto

Atomic OrbitalsValence Bond theory

Molecular Orbital Theory

Klein: 1.6 – 1.9

• Experimental data shows that electrons, like light and photons, behave as BOTH particles and waves.

• Orbital theory that was developed from this observation offers the ability to make fairly accurate predictions. Like a lake’s wave, an electron’s wavefunction can be (+), (-), or

ZERO.

Atomic Orbitals

• Orbitals are mathematically derived from wavefunctions. (Solutions for values of ℓ.)

Remember the four q.n.: n (principal), ℓ (orbital), mℓ (magnetic), ms (spin)

• Orbital regions can be (-), (+), or ZERO based on mℓ .

• In the example on the right of a p-orbital, ℓ = 1, there are three possible values for mℓ . The point where mℓ = 0 is referred to as a Node or nodal plane.

• The sign of mℓ is important in considering orbital overlap and bond formation.

Atomic Orbitals

Atomic Orbitalss and p orbitals

Atomic Orbitals Molecular Orbital (MO)

• Atomic orbitals mix to form molecular orbitals

• The total number of molecular orbitals (bonding + non- and anti bonding orbitals) equal the total number of atomic orbitals

• s bond is formed by overlapping of two s orbitals

• A bond occurs when certain atomic orbitals overlap. These overlapping orbitals are like waves.

• Only constructive interference results in a bond.

MO & Valence Bond Theories

In-phase overlap of s atomic orbitals form a bonding MO (no node);

Out-of-phase overlap forms an antibonding MO (has node)

A single bond is a s bond with a bond order of 1.

A sigma bond (s) is also formed by end-on overlap of two p orbitals

Double bonds have 1 s and 1 p bond with a bond order of 2.A p bond is weaker than a s bond.A double bond is shorter and stronger than a single bond.

Molecular Orbital Theory• Consider the MOs for CHBr3:

There are many areas of atomic orbital overlap. Notice how the MOs extend over the entire molecule. Each image represents ONE orbital, which depending on

its energy can be bonding (lowest) or non-bonding (higher) or anti-bonding (highest).

Pi bond (p) is formed by sideways overlap of two parallel p orbitals

Mixing Atomic OrbitalsHybridization of s and p orbitals

Single Bonds (Methane)

Hybridization of s and p atomic orbitals:

The atomic orbitals used in bond formation determine the bond angles

• Tetrahedral bond angle: 109.5°

• Electron pairs spread themselves into space as far from each other as possible

Hybrid Orbitals of Ethane

Practice:CONCEPTUAL CHECKPOINT 1.19

Bonding in Ethene: A Double Bond

Double bonds have 1 pand 1 s bond. A double bond is shorter and stronger than a single bond.

Practice: CONCEPTUAL CHECKPOINT 1.20

• MO theory provides a similar theoretical picture: NOTE: the red and blue regions are part of the same

orbital.

Ethene: Molecular Orbitals

• The bond angle in the sp2 carbon is 120°

• The sp2 carbon is the trigonal planar carbon

An sp2-Hybridized Carbon

http://chemconnections.org/organic/Movies%20Org%20Flash/HybridizationofCarbon.swf

Ethyne: A Triple Bondsp-Hybridized Carbon

• A triple bond consists of one s bond and two p bonds with a bond order of 3.

• Triple bonds are shorter and stronger than double bonds

• There is a bond angle of the sp carbon: 180°

Question 2.7• What is the molecular shape of each of the

carbons of tetrachloro ethene (Cl2CCCl2)?• A) tetrahedral• B) bent• C) trigonal planar• D) linear• E) trigonal pyramidal

http://chemconnections.org//organic/Movies Org Flash/hybridization.swf

Summary• A p bond is weaker than a s bond• The greater the electron density in the region of orbital overlap, the stronger is the bond• The more s character, the shorter and stronger is the bond• The more s character, the larger is the bond angle

• Being able to explain the different strengths and lengths: CONCEPTUAL CHECKPOINT 1.24.

Hybridization & Bond Strength

Reactive Carbon Atoms

Klein: 2.4

Reactive IntermediatesCarbocation

Reactive IntermediatesRadical

Reactive IntermediatesCarbanion