Midterm 2009
Chem 201/281: Inorganic Chemistry 1
Mar 17, 2009
Chem 201/281: Modern Inorganic Chemistry / Inorganic Chemistry 1 Midterm 2 Dr. Audrey H. Moores Tuesday March 17th, 6:00- 9.00 PM
Exam version
A
McGill ID
Student name
Instructions: 1. Please write your name and student i.d. on this cover page and write your exam version on your McGill Booklet. 2. At the end you will need to hand in all examination paper: the exam questions and all your McGill booklets, even unused ones. 3. This exam contains 9 pages. You may unstaple the sheets if you want to. 4. You have to follow the rules and policies of McGill University Academic Integrity.
Description of the exam: 1. There are two parts to the exam: the first part (A.) consists of exercises (answer directly on the sheet). The second part (B.) contains two problems (answer on the McGill booklets). 2. Question marks are written in bold the total is 100 points. 3. Appendices (p. 7-9) comprise A: the periodic tables of the elements B: Selected character tables C: point group assignment tree 4. In the whole midterm, I will use the Cram representation, unless specified otherwise. Make sure you keep this in mind and do the same in all your drawings 5. Make sure you always draw the skeleton of the molecule in all molecular and atomic orbitals. I want this:
not that:
Allowed and not allowed auxiliaries: 1. 2. 3. 4.
This is a closed book examination Calculators are not allowed. Translation dictionaries are not allowed Molecular models are allowed
Good luck!
Dr. Audrey H. Moores
1/9
Chem 201/281: Inorganic Chemistry 1
Mar 17, 2009
1. Exercises (please answer directly on the sheet) A. True/False (14 points) False True
Definition or statement 1)
A paramagnetic molecule is a molecule that possesses two unpaired electrons with parallel spins.
2)
Atomic orbital can only interact if they belong in the same representation
3)
4 electrons interactions lead to a global antibonding interaction because usually the 4 electrons come from different levels of energy. An MO of a molecule does not necessarily have to belong in a representation of the point group of the molecule.
4) 5)
is antibonding because the probability of finding an electron right in the middle of the two atoms is zero.
6)
The intensity of the stabilization and of the destabilization depends solely on the overlap between the interacting atomic orbitals
7)
In the MO diagramme of H He ,
is the destabilized orbital.
B. Molecular orbital representations (20 points) Here are 10 molecules and one of their MOs. For each of these molecules and MOs, answer the following questions. Please answer in the table below: a) What is the point group of the molecule? b) What is the representation of the MO? c) What is the dimension of this representation? d) If the representation is of dimension 2 or above, draw the other MO(s) involved in the same representation (limit yourself to the MO(s) of same energy). Otherwise leave blank. Here is a molecule and one of its MOs 1)
a)
b)
c)
d)
O H
H
Dr. Audrey H. Moores
2/9
Chem 201/281: Inorganic Chemistry 1 2)
Mar 17, 2009
H H
3)
B
H
H H
B
4)
H
N
H H
H
5)
H H
6)
H F
7)
O O
8)
C O
9)
H
H H
10)
H O
H
H
2. PROBLEMS (please answer on the McGill booklets) * marked questions are questions that are independent from previous answers. A. Be2 and O2 (33 points) x A
A
y
z
1) A2 diagramme Dr. Audrey H. Moores
3/9
Chem 201/281: Inorganic Chemistry 1
Mar 17, 2009
a) Draw the AOs you will use. * b) What is the point group of the molecule? * c) Using overlap considerations, build the MO diagramme of A2, neglecting the interaction between s and p orbitals. d) Take the second orbital from the bottom. Retrieve the character table of the point group found in b). For each operation of symmetry, apply the operation to the orbital and draw the result. e) Assign representation to each of the orbital you found in c). f) List two pairs of OMs that have a good symmetry to interact. In a new diagramme, picture these two interactions, placing the s OMs on one side and the p ones on the other. Draw the new MOs formed. 2) Be2 diagramme a) What is the consequence of the secondary interaction described in 1) f) on the order of the MOs in the case of Be2? Draw the final MO diagramme of Be2, with everything, levels and MOs. b) How many valence electrons are available in Be2? Fill out the MO diagramme with them. * c) Describe the bonding scheme of the molecule. What can you say about this molecule? 3) O2 diagramme a) What is the consequence of the secondary interaction described in 1) f) on the order of the MOs in the case of O2? Draw the final MO diagramme of O2, with everything, levels and MOs. b) How many electrons are available in O2? Fill out the MO diagramme with them.* c) Describe the bonding scheme of the molecule. What can you say about this molecule?
B. Methane (33 points): x H H
H H
y
z
1) Methane MO diagramme a) Draw the atomic orbitals at play in methane. * b) What is the point group of methane? * c) Assign representation to the AOs of the carbon atom d) Combine the orbitals on Hs to match the representations of the point group. e) Assign representation to the combined AOs found in d) f) Build the MO diagramme of methane. Hint: the level of the s of H is intermediate between the s of C and the p of C. g) How many valence electrons are available? * h) Fill out the MO diagramme with these electrons. i) Describe the bonding scheme of the molecule.
Dr. Audrey H. Moores
4/9
Chem 201/281: Inorganic Chemistry 1
Mar 17, 2009
2) Methane deprotonation Let’s consider the following reaction: -
CH3 +
H+
H H
H H
a) Draw the structure of CH3- using Lewis theory and VSEPR. * b) Build the MO diagramme of CH3-. Do it step by step following the general method we saw in class and we have been using for methane in 1). Note: Points will be given to each step, don’t miss any! Hint: the z axis is the principal axis of the molecule. c) How many valence electrons are available, fill out your MO diagramme and describe the bonding scheme. * d) What MO(s) of CH3- will interact with H+ to form methane?
Dr. Audrey H. Moores
5/9
Chem 201/281: Inorganic Chemistry 1
Mar 17, 2009
Appendix A: the periodic table of the elements:
Dr. Audrey H. Moores
6/9
Chem 201/281: Inorganic Chemistry 1
Mar 17, 2009
Appendix B: Character tables:
Dr. Audrey H. Moores
7/9
Chem 201/281: Inorganic Chemistry 1
Dr. Audrey H. Moores
Mar 17, 2009
8/9
Chem 201/281: Inorganic Chemistry 1
Mar 17, 2009
Appendix C: point group assignment tree Assign point group as : Td (tetrahedron) Oh (octahedron) Ih (icosahedron)
YES
Is the molecule a tetrahedron, an octahedron or an icosahedron?
NO YES
Does it have a mirror plane, σ?
Does it have an axis?
Cs
NO NO YES
Does it have a centre of symmetry, i?
Find the principal axis Cn*
YES
Ci
NO
C1 YES
Does it have nC2 axes perpendicular to Cn?
NO
Does it have a horizontal mirror plane, σh?
YES
NO
Does it have a horizontal mirror plane, σh?
Cnh YES
Cnv
Does it have a vertical mirror plane, σv? NO
Cn
NO YES
Does it have n vertical mirror planes, nσv?
Dnh Dnd
YES
NO
Dn * n can any number between (and including) 2 and ∞ |If three C2 axis, verify if one isn’t also improper
Dr. Audrey H. Moores
9/9
Mar 17, 2009
Chem 201/281: Modern Inorganic Chemistry / Inorganic Chemistry 1 Midterm 2 Dr. Audrey H. Moores Tuesday March 17th, 6:00- 9.00 PM
Exam version
A
McGill ID
Student name
Instructions: 1. Please write your name and student i.d. on this cover page and write your exam version on your McGill Booklet. 2. At the end you will need to hand in all examination paper: the exam questions and all your McGill booklets, even unused ones. 3. This exam contains 9 pages. You may unstaple the sheets if you want to. 4. You have to follow the rules and policies of McGill University Academic Integrity.
Description of the exam: 1. There are two parts to the exam: the first part (A.) consists of exercises (answer directly on the sheet). The second part (B.) contains two problems (answer on the McGill booklets). 2. Question marks are written in bold the total is 100 points. 3. Appendices (p. 7-9) comprise A: the periodic tables of the elements B: Selected character tables C: point group assignment tree 4. In the whole midterm, I will use the Cram representation, unless specified otherwise. Make sure you keep this in mind and do the same in all your drawings 5. Make sure you always draw the skeleton of the molecule in all molecular and atomic orbitals. I want this:
not that:
Allowed and not allowed auxiliaries: 1. 2. 3. 4.
This is a closed book examination Calculators are not allowed. Translation dictionaries are not allowed Molecular models are allowed
Good luck!
Dr. Audrey H. Moores
1/9
Chem 201/281: Inorganic Chemistry 1
Mar 17, 2009
1. Exercises (please answer directly on the sheet) A. True/False (14 points) False True
Definition or statement 1)
A paramagnetic molecule is a molecule that possesses two unpaired electrons with parallel spins.
2)
Atomic orbital can only interact if they belong in the same representation
3)
4 electrons interactions lead to a global antibonding interaction because usually the 4 electrons come from different levels of energy. An MO of a molecule does not necessarily have to belong in a representation of the point group of the molecule.
4) 5)
is antibonding because the probability of finding an electron right in the middle of the two atoms is zero.
6)
The intensity of the stabilization and of the destabilization depends solely on the overlap between the interacting atomic orbitals
7)
In the MO diagramme of H He ,
is the destabilized orbital.
B. Molecular orbital representations (20 points) Here are 10 molecules and one of their MOs. For each of these molecules and MOs, answer the following questions. Please answer in the table below: a) What is the point group of the molecule? b) What is the representation of the MO? c) What is the dimension of this representation? d) If the representation is of dimension 2 or above, draw the other MO(s) involved in the same representation (limit yourself to the MO(s) of same energy). Otherwise leave blank. Here is a molecule and one of its MOs 1)
a)
b)
c)
d)
O H
H
Dr. Audrey H. Moores
2/9
Chem 201/281: Inorganic Chemistry 1 2)
Mar 17, 2009
H H
3)
B
H
H H
B
4)
H
N
H H
H
5)
H H
6)
H F
7)
O O
8)
C O
9)
H
H H
10)
H O
H
H
2. PROBLEMS (please answer on the McGill booklets) * marked questions are questions that are independent from previous answers. A. Be2 and O2 (33 points) x A
A
y
z
1) A2 diagramme Dr. Audrey H. Moores
3/9
Chem 201/281: Inorganic Chemistry 1
Mar 17, 2009
a) Draw the AOs you will use. * b) What is the point group of the molecule? * c) Using overlap considerations, build the MO diagramme of A2, neglecting the interaction between s and p orbitals. d) Take the second orbital from the bottom. Retrieve the character table of the point group found in b). For each operation of symmetry, apply the operation to the orbital and draw the result. e) Assign representation to each of the orbital you found in c). f) List two pairs of OMs that have a good symmetry to interact. In a new diagramme, picture these two interactions, placing the s OMs on one side and the p ones on the other. Draw the new MOs formed. 2) Be2 diagramme a) What is the consequence of the secondary interaction described in 1) f) on the order of the MOs in the case of Be2? Draw the final MO diagramme of Be2, with everything, levels and MOs. b) How many valence electrons are available in Be2? Fill out the MO diagramme with them. * c) Describe the bonding scheme of the molecule. What can you say about this molecule? 3) O2 diagramme a) What is the consequence of the secondary interaction described in 1) f) on the order of the MOs in the case of O2? Draw the final MO diagramme of O2, with everything, levels and MOs. b) How many electrons are available in O2? Fill out the MO diagramme with them.* c) Describe the bonding scheme of the molecule. What can you say about this molecule?
B. Methane (33 points): x H H
H H
y
z
1) Methane MO diagramme a) Draw the atomic orbitals at play in methane. * b) What is the point group of methane? * c) Assign representation to the AOs of the carbon atom d) Combine the orbitals on Hs to match the representations of the point group. e) Assign representation to the combined AOs found in d) f) Build the MO diagramme of methane. Hint: the level of the s of H is intermediate between the s of C and the p of C. g) How many valence electrons are available? * h) Fill out the MO diagramme with these electrons. i) Describe the bonding scheme of the molecule.
Dr. Audrey H. Moores
4/9
Chem 201/281: Inorganic Chemistry 1
Mar 17, 2009
2) Methane deprotonation Let’s consider the following reaction: -
CH3 +
H+
H H
H H
a) Draw the structure of CH3- using Lewis theory and VSEPR. * b) Build the MO diagramme of CH3-. Do it step by step following the general method we saw in class and we have been using for methane in 1). Note: Points will be given to each step, don’t miss any! Hint: the z axis is the principal axis of the molecule. c) How many valence electrons are available, fill out your MO diagramme and describe the bonding scheme. * d) What MO(s) of CH3- will interact with H+ to form methane?
Dr. Audrey H. Moores
5/9
Chem 201/281: Inorganic Chemistry 1
Mar 17, 2009
Appendix A: the periodic table of the elements:
Dr. Audrey H. Moores
6/9
Chem 201/281: Inorganic Chemistry 1
Mar 17, 2009
Appendix B: Character tables:
Dr. Audrey H. Moores
7/9
Chem 201/281: Inorganic Chemistry 1
Dr. Audrey H. Moores
Mar 17, 2009
8/9
Chem 201/281: Inorganic Chemistry 1
Mar 17, 2009
Appendix C: point group assignment tree Assign point group as : Td (tetrahedron) Oh (octahedron) Ih (icosahedron)
YES
Is the molecule a tetrahedron, an octahedron or an icosahedron?
NO YES
Does it have a mirror plane, σ?
Does it have an axis?
Cs
NO NO YES
Does it have a centre of symmetry, i?
Find the principal axis Cn*
YES
Ci
NO
C1 YES
Does it have nC2 axes perpendicular to Cn?
NO
Does it have a horizontal mirror plane, σh?
YES
NO
Does it have a horizontal mirror plane, σh?
Cnh YES
Cnv
Does it have a vertical mirror plane, σv? NO
Cn
NO YES
Does it have n vertical mirror planes, nσv?
Dnh Dnd
YES
NO
Dn * n can any number between (and including) 2 and ∞ |If three C2 axis, verify if one isn’t also improper
Dr. Audrey H. Moores
9/9
