Chapters 1 & 2 General Chemistry Review Electronic Structure and Bonding Molecular Representations
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
ketone aldehyde carboxylic acid ester (carboxylic acid ester) Draw bond-line structures for each of the four molecules. 1. 2. 3. 4.
Introduction to Organic Functions (Functional Groups) (Klein 2.3) ketone 1. aldehyde 2. carboxylic acid 3. ester (carboxylic acid ester) 4. Worksheet 3: Organic Functional Groups (2 Sudoku) http://chemconnections.org/organic/chem226/226assign-12.html#Worksheets Worksheet 4: Functions, Polarity, Formal Charge http://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-LineStructures / Drawings Empirical Formula? Molecular formula? C7H16O C7H16O Bond-Line Structure?
Question 2.3 • The bond-line representation for (CH3)2CHCH2CH2CHBrCH3 is • A) B) • C) D)
Question 2.4 Select the best condensed structural formula for the following bond-line structure: • (CH3)2CHCH2COHOHCOH • CH3CH3CHCH2C(OH)2CHO • (CH3)2CHCH2C(OH)2CHO • (CH3)2CHCH2C(OH)2COH • CH3CHCH3CH2C(OH)2CHO
Line Drawing and Ball & Stick 8.16 Å (0.816 nm) http://chemconnections.org/COT/chemical-communication/ChemComm.html
Question 2.5 While on-line, examine the jmol-structure on the left. Which one of the formulas or structural renderings that follow is correct? http://chemconnections.org/organic/chem226/Labs/VSEPR/acetic-acid.html
Worksheet 2: Structures, Formulas & Orbitals http://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) six SEE: 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 1 http://chemconnections.org/COT/organic1/VSEPR/
Very Large Molecules:DNA http://www.umass.edu/microbio/chime/beta/pe_alpha/atlas/atlas.htm Views & Algorithms 10.85 Å 10.85 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 Molecules http://info.bio.cmu.edu/courses/03231/ProtStruc/ProtStruc.htm B-DNA: Size, Shape & Self Assembly 46 Å Rosalind Franklin’s Photo 12 base sequence (1953-2003) http://molvis.sdsc.edu/pdb/dna_b_form.pdb
AtomicOrbitalsValence Bond theoryMolecular Orbital Theory Klein: 1.6 – 1.9
Atomic Orbitals • 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 = 0is referred to as a Node or nodal plane. • The sign of mℓ is important in considering orbital overlap and bond formation.
Atomic Orbitals s 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 sorbitals
MO & Valence Bond Theories • A bond occurs when certain atomic orbitals overlap. These overlapping orbitals are like waves. • Only constructive interference results in a bond.
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).
Mixing Atomic Orbitals Hybridization 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 p and 1 s bond. A double bond is shorter and stronger than a single bond. Practice: CONCEPTUAL CHECKPOINT 1.20
Ethene: Molecular Orbitals • MO theory provides a similar theoretical picture: • NOTE: the red and blue regions are part of the same orbital.
An sp2-Hybridized Carbon • The bond angle in the sp2 carbon is 120° • The sp2 carbon is the trigonal planar carbon http://chemconnections.org/organic/Movies%20Org%20Flash/HybridizationofCarbon.swf
Ethyne: A Triple Bond sp-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
Hybridization & Bond Strength • Being able to explain the different strengths and lengths: CONCEPTUAL CHECKPOINT 1.24.
ReactiveCarbon Atoms Klein: 2.4
Reactive Intermediates Carbocation
Reactive Intermediates Radical
Reactive Intermediates Carbanion