Honors Organic Chemistry Name: ______
Unit 1 Packet: Lewis Structures, Resonance, Formal Charge, VSEPR, Hybridization, and Isomerism Honors Organic Chemistry Key Terms For Unit 1
General
Organic Chemistry Structural Isomerism
Isomerism Geometric Isomerism
Bonding
Anion Hund’s Rule Sigma bond (σ)
Bond Angle Hybridization sp hybrid orbital
Bond Length Ionic Bond sp2 hybrid orbital
Cation Line Angle sp3 hybrid orbital
Covalent Bond Non-polar covalent bond Tetrahedron
Double Bond Octet Rule Trigonal Planar
Electronegativity Pauli exclusion Principle Valence Electrons
Formal Charge Polar covalent bond Valence Shell
Full Octet Pi bond (π) Valence Shell Electron- Pair Repulsion Hindered Rotation Resonance hybrid
Nomenclature
Alcohol Carboxyl group Functional Group
Aldehyde Carboxylic Acid Ketone
Carbonyl group Ether
Lewis Structures
History: Honors Organic Chemistry
Purpose:
Process: - CH4 COCl2 NO3 1. Predict the Arrangement of the atoms:
2. Count up the valence electrons
3. Connect the surrounding atoms to the central atom with single bond (one shared pair)
4. Determine how many electron pairs you have left
5. Place lone pairs around terminal atoms to satisfy octet (stick any leftovers on central atom)
6. If the central atom has not achieved an octet, form multiple bonds to do so
Lewis Structures – Additional Practice Honors Organic Chemistry
2- H2O CO3
NH3 SOCl2
CH2O C2H4
Resonance Structures
Often, it is possible to draw more that one legal Lewis structure for a molecule.
2- e.g. SO4
Expanded Octet:
Each of these structures fulfills the requirements of a Lewis structure, therefore, they are valid resonance structures. No single one of these resonance structures gives a complete picture of what the ion looks like. A resonance structure is a lewis structure that contributes to the overall resonance hybrid of a molecule or polyatomic ion. Resonance Hybrids – What does a molecule really look like?
All of the resonance structures that can be drawn for a sulfate ion are not created equal – how do we decide which ones contribute most to the actual picture of what a molecule looks like? To do this, we have to minimize the formal charge of each atom.
CO2
By minimizing the formal charge on each atom, we can isolate the resonance structure that best represents what a molecule or ion looks like.
Try some others:
2- C2O4 Honors Organic Chemistry
2- SO3
General Guidelines for Resonance Structures
1. Try to draw structures that are as low in energy as possible 2. The best structures tend to have the maximum number of bonds and the most octets 3. When structures are equivalent in terms of bonds and octets, minimize formal charge to find the more stable structure 4. All structures must be valid. Only electrons may be moved to change between structures, bonding sequence of atoms must remain the same. 5. Use curved arrows to show the movement of electrons. Only move lone pairs and multiple bonds. 6. Separate resonance structures by a double headed arrow. 7. Resonance stabilization is very important when it delocalizes or spreads a charge over two or more atoms 8. Negative formal charges are more stable on atoms with higher electronegativities. Worksheet – Resonance and Formal Charge
1. For each of the following compounds, draw the important resonance structures. Indicate which structures are major and minor contributors or whether they have the same energy a. - [H2CNO2]
c. + [H2COH]
:O: || b. H – C – NH2
d. H2CNN Honors Organic Chemistry
:O: :O: || .. || g. H – C – CH – C – H
e. - [H2CCN]
:O: (-) .. || .. f. H2C – C – O – CH3 ..
2. Draw the important resonance structures for the following molecules and ions
a. + b. - H2C = CH – CH2 H2C = CH – CH2
Summary of Bonding Patterns
Atom Valence Positively Neutral Negatively Electrons Charged Charged
B
C Honors Organic Chemistry
N
O
Halogen
Important Note: The bonds shown do not always have to be single bonds
Ex:
VSEPR Theory
VSEPR:
VSEPR theory is used to predict the 3-D geometry of the terminal atoms around the central atom of a molecule – VSEPR theory tells us the shape of the molecule.
How to determine the 3-D geometry of a molecule from a Lewis Structure
Ex: H2O Honors Organic Chemistry
Parent Shape
1. Count the number of regions of electronLinear density around the central atom
Trigonal Planar This tells you the parent shape of the molecule (see below) 2. Use the number of bonded regions of density and the total regions of density to determine the actual shape of the molecule
Tetrahedron
Ex: SCl4 3. Remember that lone pairs repel more strongly than bonded pairs, so in a trigonal bipyramid, place them on the plane as opposed to the axis
Trigonal Bipyramid
Predict the parent shape and the 3-D geometry of the following molecules:
NH3 SiO2
IF3 IF5
Octahedron
Pentagonal Bipyramid Honors Organic Chemistry
Hybridization
Consider the molecule methane, CH4. One carbon atom bonded to four different hydrogen atoms.
Electron Configurations:
C: ______H: ___ 1s 2s 2p 1s
Hund’s Rule: Honors Organic Chemistry
Pauli Exclusion Principle:
We know that single bonds are formed by the overlap of two orbitals that each have one unpaired electron – to be able to form 4 bonds to carbon, one electron will have to be promoted from the 2s to the empty 2p orbital.
C: ______1s 2s 2p
At present, of the four bonds that carbon is making to hydrogen, there are three “1s overlapping 2p” bonds and one “1s overlapping 2s” bond. From your knowledge of s and p orbitals, draw a diagram of what this molecule would look like.
There are a couple of problems with the diagram above.
First, experimental evidence shows us that the bond angles for the above molecule are incorrect – all 4 hydrogen atoms should be equivalently spaced 109.5° from one another.
Second, all experimental evidence tells us that the four bonds in methane are equal in energy.
To take into consideration these two problems, a bonding theory called hybridization was devised
Hybridization:
Hybridization Continued sp hybrids: produced from one “s” and one “p” orbital. Two “p” orbitals remain unchanged and available for π bonding.
Ex: Beryllium in BeCl2 – two sp hybrid orbitals form two σ bonds. Drawing
______2p Electron 2p Hybridization 2p Honors Organic Chemistry ___ Promotion ___ ______2s 2s sp
Ex: Carbon in C2H2 – two sp hybrid orbitals form two σ bonds. Two “p” orbitals remain available for π bonding. Drawing
______2p Electron 2p Hybridization 2p ___ Promotion ___ ______2s 2s sp
sp2 hybrids: produced from one “s” and two “p” orbitals. One “p” orbital remains unchanged and available for π bonding.
2 Ex: Boron in BeF3 – three sp hybrid orbitals form three σ bonds. Drawing
______2p Electron 2p Hybridization 2p ___ Promotion ___ ______2s 2s sp2
2 Ex: Carbon in C2H4 – three sp hybrid orbitals form two σ bonds. One “p” orbital remains available for π bonding. Drawing
______2p Electron 2p Hybridization 2p ___ Promotion ___ ______2s 2s sp2
sp3 hybrids: produced from one “s” and three “p” orbitals.
3 Ex: Carbon in CH4 – four sp hybrid orbitals form four σ bonds. Drawing
______2p Electron 2p Hybridization ___ Promotion ___ ______2s 2s sp3
sp3 hybrids continued:
3 Ex: Oxygen in H2O – two sp hybrid orbitals with unpaired electrons will form two σ bonds. The two sets of paired electrons exist as lone pairs. Drawing
______There is no electron 2p Electron promotion because Hybridization Honors Organic Chemistry ___ Promotion all orbitals are occupied ______2s sp3
sp3d hybrids: produced from one “s”, three “p”, and one “d” orbitals.
3 Ex: Phosphorus in PCl5 – five sp d hybrid orbitals form five σ bonds.
______3d 3d ______3p Electron 3p Hybridization 3d ___ Promotion ___ ______3s 3s sp3d
3 Ex: Sulfur in SF4 – five sp d hybrid orbitals form four σ bonds. One lone pair remains.
______3d 3d ______3p Electron 3p Hybridization 3d ___ Promotion ___ ______3s 3s sp3d
3 Ex: Iodine in IF3 – five sp d hybrid orbitals form three σ bonds. Two lone pairs remain.
______3d 3d ______3p Electron 3p Hybridization 3d ___ Promotion ___ ______3s 3s sp3d
3 Ex: Xenon in XeF2 – five sp d hybrid orbitals form two σ bonds. Three lone pairs remain.
______3d 3d ______3p Electron 3p Hybridization 3d ___ Promotion ___ ______3s 3s sp3d
Worksheet: Hybridization and Lewis Structures
1. For each of the following, add lone pairs where needed to form octets, predict the hybridization and bond angles for the circled atoms. Honors Organic Chemistry
a) O b) H H c) CH3 || | | | H – O – C – O H – C – C – O CH3 – N – CH3 | | | H H CH3 d) H H e) H f) | | | H – C – C Cl – C = C – C = N – H H – C ≡ C – H | | | | H H H H
a. Hybridization: ______Bond Angle: ______
b. Hybridization: ______Bond Angle: ______
c. Hybridization: ______Bond Angle: ______
d. Hybridization: ______Bond Angle: ______e. i. Carbon - Hybridization: ______Bond Angle: ______
ii. Nitrogen - Hybridization: ______Bond Angle: ______
f. Hybridization: ______Bond Angle: ______
2. From question #1, which structures are ions?
3. What type of orbitals are overlapping between the atoms in the following? a) b) c)
H H H H | .. | | | .. H – C = O: H – C = C = C – H H – C – O: | | H H
4. Draw Lewis Structures for the following. Remember, hydrogen and halogens do not make double bonds. Honors Organic Chemistry
+ a. CO2 d. N2H4 g. NO2
b. SeCl4 e. ICl3 h. BF3
+ -2 c. NH4 f. SiO3
5. State the hybridization of each central atom from Question #4
a. ______d. ______g. ______
b. ______e. ______h. ______
c. ______f. ______
.. 6. Use wedges and dashes for σ bonds to draw an orbital diagram of CH3 – C – O: Draw any “p” orbitals, label bond angles. || | :O: H
Worksheet – Bonding and Hybridization
1. For each of the following compounds: a. Give the hybridization for each atom except hydrogen b. Give the approximate bond angles for each atom except hydrogen c. Draw an orbital diagram using lines, wedges and dashed lines for sigma bonds. Draw the “p” orbital interaction for pi bonds
I. + III. H3O CH3 – C = N – H | H
II. + IV. (CH3)4N CH2O
2. For each of the following: a. Draw the Lewis structure b. Indicate what type of orbitals are overlapping to form each bond c. Give approximate bond angles for each atom except hydrogen
I. CH3 – C ≡ C – CHO II. H2N – CH2 – CN Honors Organic Chemistry
III. (CH3)2NH IV. CH3 – CH = C(CH3)2
3. Predict the hybridization and geometry of each carbon atom in the following anion:
O (-) || .. CH3 – C – CH2
4. On a separate sheet of paper, draw orbital diagrams of the pi bonding in the following compounds. Use lines, dashes and wedges to show sigma bonds a. CH3COCH3 b. CH3 – C ≡ C – CHO c. Cis CH3 – CH = CH – CH2CH3 (circle the six coplanar atoms in this molecule) Worksheet – Bonding Part 2
1. 2-pentyne has the formula CH3CCCH2CH3. Use dashed lines and wedges to draw a 3-D diagram of this molecule. Draw p orbitals as clouds. Circle the four atoms that are in a straight line.
2. Which of the following show geometric isomerism? Draw the cis and trans isomers of the ones that do.
a. CH2=C(CH3)2
b. CH3CH=CHCH3
c. CH3C≡CCH3 Honors Organic Chemistry
d. e. CH3CH = C – CH2CH3 | CH2CH3
Worksheet – Bonding Part 2 (cont.)
3. State the relationships between the following pairs of structures. Your choices are: identical compound, geometric isomers, structural isomers, totally different molecules.
a. CH3CH2CH2CH3 and (CH3)3CH
b. CH2 = CH – CH2Cl and CHCl = CHCH3
c. CH3 CH3 CH3 \ / and \ CH = CH CH = CH \ CH3
d. CH3 CH3 CH2 \ / and || CH = CH CH3 – C – CH3
e. and
f. and
g. and Honors Organic Chemistry
Material Covered on the Unit 1 Test
1. Be able to define and give examples of the all of the key terms on page 2 of this packet
2. Know the structure and names of all functional groups mentioned in page 2 of this packet
3. Be able to draw valid Lewis structures for polyatomic ions and organic molecules
4. Be able to assign formal charges to atoms in Lewis structures and also be able to determine which structures are the major and minor contributors to the resonance hybrid
5. Be able to predict bond angles and molecular geometry (shape) from Lewis structures
6. Be able to determine the hybridization that carbon, nitrogen, oxygen and sulfur atoms have undergone in a molecule or ion
7. Memorize the relative order of electronegativities of the following elements: F, O, Cl, N, Br, S, I, C, P, H.
8. Be able to assign polarity to bonds in Lewis structures
9. Be able to draw Lewis structures and line-angle diagrams for structural isomers if given a molecular formula
10. Be proficient in the use of curved arrows to show electron movement when drawing contributing resonance structures
11. Be able to write and interpret condensed structural formulas
12. Draw orbital diagrams of sigma and pi bonding
13. Be able to draw representations of 3-D molecules by using wedges and dashed lines