CHE 166 Problem Set #10

Workshop CHE 166
Problem Set #10

1. Give the total number of valance electrons and the electron-pair and molecular geometries for the following:

(a) ClO₂^{^-}
(b) SO₃
(c) PCl₃
(d) BH₄^{^-}
(e) SO₃^²^{^-}
(f) ICl₃
(g) SCl₂
(h) ICl₂^{^-}
(i) TeF₄
(j) AsF₃
(k) PF₆^{^-}

2. The molecules NF₃, BF₃ and ClF₃ all have molecular formulas of the type XF₃, but the molecules have different geometries. Predict the shape of each molecule and explain the origin of the differing shapes.

3. Predict whether the following molecules are polar or nonpolar:

(a) CCl₄
(b) CS₂
(c) SO₃
(d) SF₄
(e) NF₃
(f) PF₅
(g) IF
(h) SO₂
(i) PCl₃
(j) SF₆

4. Despite the larger electronegativity difference between the bonded atoms, BeCl₂ _(g) has no dipole moment, whereas SCl₂ _(g)does possess one. Account for this difference in polarity.

5.

(a) Starting with a boron atom in its ground-state electron configuration, describe the steps needed to construct hybrid orbitals appropriate to describe the bonding in BF₃.
(b) What is the name given to the hybrid orbitals constructed in (a)?
(c) Are there any valence orbitals of B that are left unhybridized? If so, how are they oriented relative to the hybrid orbitals?

6. Indicate the hybrid orbital set used by the central atom in each of the following:

(a) BH₄^{^-}
(b) NH₃
(c) BI₃
(d) PF₆^{^-}
(e) SO₄^²^{^-}
(f) CS₂
(g) H₃O^⁺

7. The carbon atom in CH₄ can not participate in multiple bonding, whereas that in formaldehyde, H₂CO, does. Explain this observation by using the hybridization at the carbon atom.

8. From their Lewis structures, determine the number of s and p bonds in each of the following molecules or ions:

(a) CO₂
(b) NCS^{^-}
(c) SO₄^²^{^-}
(d) HCO(OH) which has a H and two oxygens attached to C.

9. Identify the types of intermolecular forces that are present in each of the following substances and select the substance in each pair that has the highest boiling point:

(a) C₆H₁₄ or C₈H₁₈
(b) C₃H₈ or CH₃OCH₃
(c) CH₃OH or CH₃SH
(d) NH₂NH₂ or CH₃CH₃

10. Molecular nitrogen, N₂, and carbon monoxide, CO, are isoelectronic and nearly equal in molecular mass. Explain why the boiling point of CO₍_l₎ is slightly higher than that of N₂ ₍_l₎.

11. The dipole moments of HCl and HI are 1.08 D and 0.44 D respectively.

(a) Which of these substances will have the greater dipole-dipole interactions?
(b) Which of these substances will have the greater London dispersion forces? Give explainations with your answers.

12. How do the strengths of dispersion forces vary with molecular size? Why?

13. Which member of each of the following pairs of substances would you expect to have the higher boiling point?

(a) N₂ or O₂
(b) CH₄ or SiO₂
(c) NaCl or CH₃Cl. Explain each answer.

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