Homework answers / question archive / Q1 (10 points) Select/Circle all that apply (questions have more than 1 correct choice) Molecule(s) with at least one atom with tetrahedral geometry CCl2F2             CH3CHCH2     H2S      CH3COCH3     ClF5 Planar molecule(s) CO2 H2S AsCl3 BrF3 ICl2- CH3COCH3 Molecules that have intermolecular hydrogen bonding NF3         H2S      CH3NH2          HF       HCN Molecules with a dipole moment NBr3      H2S      CH3NH2          HF       CO2 Q2 (10 points) Arrange the following From lowest to highest number of lone pairs of electron on the central atom H2O, XeF2, CO2, BeCl2, IF5 From lowest to highest formal charge on N i

Q1 (10 points) Select/Circle all that apply (questions have more than 1 correct choice) Molecule(s) with at least one atom with tetrahedral geometry CCl2F2             CH3CHCH2     H2S      CH3COCH3     ClF5 Planar molecule(s) CO2 H2S AsCl3 BrF3 ICl2- CH3COCH3 Molecules that have intermolecular hydrogen bonding NF3         H2S      CH3NH2          HF       HCN Molecules with a dipole moment NBr3      H2S      CH3NH2          HF       CO2 Q2 (10 points) Arrange the following From lowest to highest number of lone pairs of electron on the central atom H2O, XeF2, CO2, BeCl2, IF5 From lowest to highest formal charge on N i

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Q1 (10 points)

Select/Circle all that apply (questions have more than 1 correct choice)

1. Molecule(s) with at least one atom with tetrahedral geometry

CCl₂F₂             CH₃CHCH₂     H₂S      CH₃COCH₃     ClF₅

2. Planar molecule(s)

CO₂ H₂S AsCl₃ BrF₃ ICl₂^- CH₃COCH₃

3. Molecules that have intermolecular hydrogen bonding

NF₃         H₂S      CH₃NH₂          HF       HCN

4. Molecules with a dipole moment

NBr₃      H₂S      CH₃NH₂          HF       CO₂

Q2 (10 points)

Arrange the following

1. 1. From lowest to highest number of lone pairs of electron on the central atom

H₂O, XeF₂, CO₂, BeCl₂, IF₅

1. 2. From lowest to highest formal charge on N

i.   ii.

iii.iv

1. 3. From lowest to highest boiling point

 

2

2

2

H₃C CH CH CH₂             H₃C CH CH CH₃

 

i.          CH3       ii.           CH3         iii.

1. 4. From weakest to strongest intermolecular force present in water (H₂O) molecules.

Write down the intermolecular forces and arrange them from weakest to strongest.

Q3) 10 Points

1. 6 points Draw the Lewis structure(s) for H₂SO₃ and SO₃^2-. Include lone pairs in your answer. Indicate all non zero formal charge on the atoms.
2. 4 points Which of the two (H₂SO₃ or SO₃^2-) has resonance structures? Show all equivalent resonance structures for that molecule

Q4 (20 points)

10 points

1. Draw the molecular orbital diagram for BC (Boron Carbide). (Label increasing energy using an arrow next to the diagram. Label each atomic and each molecular orbital)
   5. points
2. Write the molecular orbital configuration for the valence electrons in BC and BC^-.
   5. points
3. Which of the two has a stronger bond, BC or BC^-? Explain your answer.

Q5 (14 points)

5 points

An important industrial route to extremely pure ethanoic acid (acetic acid) is the reaction of methanol with carbon monoxide:

Use bond energies to calculate the heat of reaction.

Bond	kJ/mol
C?H	413
C?C	347
C?O	745
C?O	358
O?H	467
C≡O	1070

3 points

a) Which of the following would have the highest lattice energy? Why?

NaF     CsCl    MgO    MgS

6 points

b) Calculate the lattice energy (kJ/mol) of MgF₂ using the following data:

?H° (kJ/mol)

Mg(s)   Mg(g)   148 F₂(g)   2F(g)     159

Mg(g)              Mg²⁺(g) +2e^-     2188

F(g)   +   e^–         F^–(g)    –328

Mg(s)   +   F₂(g)          MgF₂(s)          –1123

Q6 (16 points)

1. Guanine and Cytosine are two DNA nucleobases. Below are the most stable Lewis structures for guanine and cytosine. Determine the hybridization and geometry around the atoms indicated with an arrow. (Lone pairs are  not  shown). Indicate the orbitals involved in each bond around the atom (distinguish sigma and pi bonds)

 

N

C

N

C

NH

2

HC

 

HC

 

NH

C

C

C

C

N

HC

N

O

H  N          NH₂      H         ^O

 

Guanine        Cytosine

Guanine (picture on left)

a.   C atom

1. Hybridization
2. Geometry
3. Orbitals involved in bonds

2. N atom

1. Hybridization
2. Geometry
3. Orbitals involved in bonds

Cytosine (picture on right)

3. N atom

1. Hybridization
2. Geometry
3. Orbitals involved in bonds

4. C atom

1. Hybridization
2. Geometry
3. Orbitals involved in bonds

Q7) 12 points

 

Determine the geometry (using the most stable Lewis structure) around the underlined atom, and draw the molecule with the correct geometry (show solid wedge and dashed bonds where appropriate). Circle if the molecule is polar or non polar

 

1. SF₄

 

 

 

 

Polar                           Non polar

 

2. CH₃COOH

 

 

 

 

 

Polar                           Non polar

 

 

3. CH₃NH₂

 

 

 

 

Polar                            Non polar

             

Q8) 8 points

Briefly compare in pictures the probability density between two nuclei for a sigma _{1s (σ 1s)} orbital with that of a sigma* _(σ*1s) orbitals. Show and label the atomic orbitals and the molecular orbitals.

 

 

 

 

 

 

 

 

 

Briefly compare in pictures the probability density between two nuclei for a pi _{2p (π 2p)} orbital with that of a pi* _(π*2p) orbitals. Show and label the atomic orbitals and the molecular orbitals. (Consider x as the bond axis)