Chemical Bonding and Molecular Geometry

Question: Using the standard enthalpy of formation data in Appendix G, determine which bond is stronger: the \({\rm{S - F}}\) bond in \({\rm{S}}{{\rm{F}}_{\rm{4}}}{\rm{(g)}}\) or in \({\rm{S}}{{\rm{F}}_{\rm{6}}}{\rm{(g)}}\)?

Question: Using the standard enthalpy of formation data in Appendix G, determine which bond is stronger: the \({\rm{P - Cl}}\) bond in \({\rm{PC}}{{\rm{l}}_{\rm{3}}}{\rm{(g)}}\) or in \({\rm{PC}}{{\rm{l}}_{\rm{5}}}{\rm{(g)}}\)?

Question: Complete the following Lewis structure by adding bonds (not atoms), and then indicate the longest bond:

Question: Use principles of atomic structure to answer each of the following: 

(a) The radius of the \({\rm{Ca}}\) atom is \({\rm{197 pm}}\); the radius of the \({\rm{C}}{{\rm{a}}^{{\rm{2 + }}}}\) ion is \({\rm{99 pm}}\). Account for the difference. 

(b) The lattice energy of \({\rm{CaO(s)}}\) is \({\rm{ - 3460 kJ/mol}}\); the lattice energy of \({{\rm{K}}_{\rm{2}}}{\rm{O}}\) is \({\rm{ - 2240 kJ/mol}}\). Account for the difference. 

(c) Given these ionization values, explain the difference between \({\rm{Ca}}\) and \({\rm{K}}\) with regard to their first and second ionization energies. 

(d) The first ionization energy of \({\rm{Mg}}\) is \({\rm{738 kJ/mol}}\) and that of \({\rm{Al}}\) is \({\rm{578 kJ/mol}}\). Account for this difference.

The lattice energy of \({\rm{LiF}}\) is \({\rm{1023 kJ/mol}}\), and the \({\rm{Li - F}}\) distance is \({\rm{200}}{\rm{.8 pm}}\). \({\rm{NaF}}\) crystallizes in the same structure as \({\rm{LiF}}\) but with a \({\rm{Na - F}}\) distance of \({\rm{231 pm}}\). Which of the following values most closely approximates the lattice energy of \({\rm{NaF}}\): \({\rm{510, 890, 1023, 1175,}}\) or \({\rm{4090 kJ/mol}}\)? Explain your choice.

For which of the following substances is the least energy required to convert one mole of the solid into separate ions? 

(a) \({\rm{MgO}}\) 

(b) \({\rm{SrO}}\) 

(c) \({\rm{KF}}\) 

(d) \({\rm{CsF}}\) 

(e) \({\rm{Mg}}{{\rm{F}}_{\rm{2}}}\)

The reaction of a metal, \({\rm{M}}\), with a halogen, \({{\rm{X}}_{\rm{2}}}\), proceeds by an exothermic reaction as indicated by this equation: \({\rm{M(s) + }}{{\rm{X}}_{\rm{2}}}{\rm{(g)}} \to {\rm{M}}{{\rm{X}}_{\rm{2}}}{\rm{(s)}}\). For each of the following, indicate which option will make the reaction more exothermic. Explain your answers.

(a) a large radius vs. a small radius for \({{\rm{M}}^{{\rm{ + 2}}}}\)

(b) a high ionization energy vs. a low ionization energy for \({\rm{M}}\) 

(c) an increasing bond energy for the halogen 

(d) a decreasing electron affinity for the halogen 

(e) an increasing size of the anion formed by the halogen

The lattice energy of \({\rm{LiF}}\) is \({\rm{1023 kJ/mol}}\), and the \({\rm{Li - F}}\) distance is \({\rm{201 pm}}\). \({\rm{MgO}}\) crystallizes in the same structure as \({\rm{LiF}}\) but with a \({\rm{Mg - O}}\) distance of \({\rm{205 pm}}\). Which of the following values most closely approximates the lattice energy of \({\rm{MgO}}\): \({\rm{256 kJ/mol, 512 kJ/mol, 1023 kJ/mol, 2046 kJ/mol,}}\) or \({\rm{4008 kJ/mol}}\)? Explain your choice.

Which compound in each of the following pairs has the larger lattice energy? Note: \({\rm{M}}{{\rm{g}}^{{\rm{2 + }}}}\) and \({\rm{L}}{{\rm{i}}^{\rm{ + }}}\) have similar radii; \({{\rm{O}}^{{\rm{2 - }}}}\) and \({{\rm{F}}^{\rm{ - }}}\) have similar radii. Explain your choices. 

(a) \({\rm{MgO}}\) or \({\rm{MgSe}}\) 

(b) \({\rm{LiF}}\) or \({\rm{MgO}}\) 

(c) \({\rm{L}}{{\rm{i}}_{\rm{2}}}{\rm{O}}\) or \({\rm{LiCl}}\) 

(d) \({\rm{L}}{{\rm{i}}_{\rm{2}}}{\rm{Se}}\) or \({\rm{MgO}}\)

Which compound in each of the following pairs has the larger lattice energy? Note: \({\rm{B}}{{\rm{a}}^{{\rm{2 + }}}}\) and \({{\rm{K}}^{\rm{ + }}}\) have similar radii; \({{\rm{S}}^{{\rm{2 - }}}}\) and \({\rm{C}}{{\rm{l}}^{\rm{ - }}}\) have similar radii. Explain your choices. 

(a) \({{\rm{K}}_{\rm{2}}}{\rm{O}}\) or \({\rm{N}}{{\rm{a}}_{\rm{2}}}{\rm{O}}\) 

(b) \({{\rm{K}}_{\rm{2}}}{\rm{S}}\) or \({\rm{BaS}}\) 

(c) \({\rm{KCl}}\) or \({\rm{BaS}}\) 

(d) \({\rm{BaS}}\) or \({\rm{BaC}}{{\rm{l}}_{\rm{2}}}\)

Which of the following compounds requires the most energy to convert one mole of the solid into separate ions? 

(a) \({\rm{MgO}}\) 

(b) \({\rm{SrO}}\) 

(c) \({\rm{KF}}\) 

(d) \({\rm{CsF}}\) 

(e) \({\rm{Mg}}{{\rm{F}}_{\rm{2}}}\)

Which of the following compounds requires the most energy to convert one mole of the solid into separate ions? 

(a) \({{\rm{K}}_{\rm{2}}}{\rm{S}}\) 

(b) \({{\rm{K}}_{\rm{2}}}{\rm{O}}\) 

(c) \({\rm{CaS}}\) 

(d) \({\rm{C}}{{\rm{s}}_{\rm{2}}}{\rm{S}}\) 

(e) \({\rm{CaO}}\)

The lattice energy of \({\rm{KF}}\) is \({\rm{794kJ/mol}}\), and the interionic distance is \({\rm{269 pm}}\). The \({\rm{Na - F}}\) distance in \({\rm{NaF}}\), which has the same structure as \({\rm{KF}}\), is \({\rm{231 pm}}\). Which of the following values is the closest approximation of the lattice energy of \({\rm{NaF}}\): \({\rm{682 kJ/mol, 794 kJ/mol, 924 kJ/mol, 1588 kJ/mol,}}\) or \({\rm{3175  kJ/mol}}\)? Explain your answer.

Explain why the \({\rm{HOH}}\) molecule is bent, whereas the \({\rm{HBeH}}\) molecule is linear.

What feature of a Lewis structure can be used to tell if a molecule’s (or ion’s) electron-pair geometry and molecular structure will be identical?

Explain the difference between electron-pair geometry and molecular structure.

Why is the \({\rm{H - N - H}}\) angle in \({\rm{N}}{{\rm{H}}_{\rm{3}}}\) smaller than the \({\rm{H - C - H}}\) bond angle in \({\rm{C}}{{\rm{H}}_{\rm{4}}}\)? Why is the \({\rm{H - N - H}}\) angle in \({\rm{NH}}_{\rm{4}}^{\rm{ + }}\) identical to the \({\rm{H - C - H}}\) bond angle in \({\rm{C}}{{\rm{H}}_{\rm{4}}}\)?

Explain how a molecule that contains polar bonds can be nonpolar.

As a general rule, \({\rm{M}}{{\rm{X}}_{\rm{n}}}\) molecules (where \({\rm{M}}\) represents a central atom and \({\rm{X}}\) represents terminal atoms; \({\rm{n = 2 - 5}}\)) are polar if there is one or more lone pairs of electrons on \({\rm{M}}\). \({\rm{N}}{{\rm{H}}_{\rm{3}}}\) (\({\rm{M = N, X = H, n = 3}}\)) is an example. There are two molecular structures with lone pairs that are exceptions to this rule. What are they?

Predict the electron pair geometry and the molecular structure of each of the following molecules or ions: 

(a) \({\rm{S}}{{\rm{F}}_{\rm{6}}}\)

(b) \({\rm{PC}}{{\rm{l}}_{\rm{5}}}\)

(c) \({\rm{Be}}{{\rm{H}}_{\rm{2}}}\)

(d) \({\rm{CH}}_{\rm{3}}^{\rm{ + }}\)

Predict the electron pair geometry and the molecular structure of each of the following ions:

1. \({{\rm{H}}_{\rm{3}}}{{\rm{O}}^{\rm{ + }}}\,\)
2. \({\rm{PC}}{{\rm{l}}_{\rm{4}}}{\rm{ - }}\)
3. \({\rm{SnC}}{{\rm{l}}_{\rm{3}}}^{\rm{ - }}\)
4. \({\rm{BrC}}{{\rm{l}}_{\rm{4}}}^{\rm{ - }}\)
5. \({\rm{IC}}{{\rm{l}}_{\rm{3}}}\)
6. \({\rm{Xe}}{{\rm{F}}_{\rm{4}}}\)
7. \({\rm{S}}{{\rm{F}}_{\rm{2}}}\)

Identify the electron pair geometry and the molecular structure of each of the following molecules:

1. \({\rm{CNIO}}\) (N is the central atom)
2. \({\rm{C}}{{\rm{S}}_{\rm{2}}}\)
3. \({\rm{C}}{{\rm{l}}_{\rm{2}}}{\rm{CO}}\)(C is the central atom)
4. \({\rm{C}}{{\rm{l}}_{\rm{2}}}{\rm{SO}}\)(S is the central atom)
5. \({\rm{S}}{{\rm{O}}_{\rm{2}}}{\rm{\;}}{{\rm{F}}_{\rm{2}}}\)(S is the central atom)
6. \({\rm{Xe}}{{\rm{O}}_{\rm{2}}}{\rm{\;}}{{\rm{F}}_{\rm{2}}}\)(Xe is the central atom)
7. \({\rm{ClOF}}_{\rm{2}}^{\rm{ + }}\)(Cl is the central atom)

Predict the electron pair geometry and the molecular structure of each of the following:

1. \({\rm{IO}}{{\rm{F}}_{\rm{5}}}\)(I is the central atom)
2. \({\rm{POC}}{{\rm{l}}_{\rm{3}}}\)(P is the central atom)
3. \({\rm{C}}{{\rm{l}}_{\rm{2}}}{\rm{SeO}}\)(Se is the central atom)
4. \({\rm{ClS}}{{\rm{O}}^{\rm{ + }}}\)(S is the central atom)
5. \({{\rm{F}}_{\rm{2}}}{\rm{SO}}\)(S is the central atom)
6. \({\rm{N}}{{\rm{O}}_{\rm{2}}}^{\rm{ - }}\)
7. \({\rm{SiO}}_{\rm{4}}^{{\rm{4 - }}}\)

Which of the following molecules and ions contain polar bonds? Which of these molecules and ions have dipole moments?

1. \({\rm{Cl}}{{\rm{F}}_{\rm{5}}}\)
2. \({\rm{Cl}}{{\rm{O}}_{\rm{2}}}{\rm{ - }}\)
3. \({\rm{TeC}}{{\rm{l}}_{\rm{4}}}^{{\rm{2 - }}}\)
4. \({\rm{PC}}{{\rm{l}}_{\rm{3}}}\)
5. \({\rm{Se}}{{\rm{F}}_{\rm{4}}}\)
6. \({\rm{P}}{{\rm{H}}_{\rm{2}}}^{\rm{ - }}\)
7. \({\rm{Xe}}{{\rm{F}}_{\rm{2}}}\)

Which of these molecules and ions contain polar bonds? Which of these molecules and ions have dipole moments?

1. \({{\rm{H}}_{\rm{3}}}{{\rm{O}}^{\rm{ + }}}\)
2. \({\rm{PC}}{{\rm{l}}_{\rm{4}}}^{\rm{ - }}\)
3. \({\rm{SnCl}}_{\rm{3}}^{\rm{ - }}\)
4. \({\rm{BrCl}}_{\rm{4}}^{\rm{ - }}\)
5. \({\rm{IC}}{{\rm{l}}_{\rm{3}}}\)
6. \({\rm{Xe}}{{\rm{F}}_{\rm{4}}}\)
7. \({\rm{S}}{{\rm{F}}_{\rm{2}}}\)

Which of the following molecules have dipole moments?

1. \({\rm{C}}{{\rm{S}}_{\rm{2}}}\)
2. \({\rm{Se}}{{\rm{S}}_{\rm{2}}}\)
3. \({\rm{CC}}{{\rm{l}}_{\rm{2}}}{\rm{\;}}{{\rm{F}}_{\rm{2}}}\)
4. \({\rm{PC}}{{\rm{l}}_{\rm{3}}}{\rm{(P is the central atom)}}\)
5. \({\rm{ClNO (N is the central atom)}}\)

Write Lewis structures for the following: (a) \({{\rm{O}}_{\rm{2}}}\) (b) \({{\rm{H}}_{\rm{2}}}{\rm{CO}}\) (c) \({\rm{As}}{{\rm{F}}_{\rm{3}}}\) (d) \({\rm{ClNO}}\) (e) \({\rm{SiC}}{{\rm{l}}_{\rm{4}}}\) (f) \({{\rm{H}}_{\rm{3}}}{{\rm{O}}^{\rm{ + }}}\) (g) \({\rm{N}}{{\rm{H}}_{\rm{4}}}^{\rm{ + }}\) (h) \({\rm{B}}{{\rm{F}}_{\rm{4}}}^{\rm{ - }}\) (i) \({\rm{HCCH}}\) (j) \({\rm{CICN}}\) (k) \({{\rm{C}}_{\rm{2}}}^{{\rm{2 + }}}\) .

Write Lewis structures for the following: (a) \({\rm{CI}}{{\rm{F}}_{\rm{3}}}\) (b) \({\rm{PC}}{{\rm{I}}_{\rm{5}}}\) (c) \({\rm{B}}{{\rm{F}}_{\rm{3}}}\) (d) \({\rm{P}}{{\rm{F}}_{\rm{6}}}^{\rm{ - }}\) .

 Identify the molecules with a dipole moment:

1. \({\rm{S}}{{\rm{F}}_{\rm{4}}}\)
2. \({\rm{C}}{{\rm{F}}_{\rm{4}}}\)
3. \({\rm{C}}{{\rm{l}}_{\rm{2}}}{\rm{CCB}}{{\rm{r}}_{\rm{2}}}\)
4. \({\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{Cl}}\)
5. \({{\rm{H}}_{\rm{2}}}{\rm{CO}}\)

The molecule XF3 has a dipole moment. Is X boron or phosphorus?

The molecule \({\rm{XC}}{{\rm{l}}_{\rm{2}}}\)has a dipole moment. Is X beryllium or sulfur?

Is the \({\rm{C}}{{\rm{l}}_{\rm{2}}}{\rm{BBC}}{{\rm{l}}_{\rm{2}}}\)molecule polar or nonpolar?

There are three possible structures for \({\rm{PC}}{{\rm{l}}_{\rm{2}}}{\rm{\;}}{{\rm{F}}_{\rm{3}}}\)with phosphorus as the central atom. Draw them and discuss how measurements of dipole moments could help distinguish among them.

Describe the molecular structure around the indicated atom or atoms:

1. The sulfur atom in sulfuric acid, H₂SO₄ [ (HO)₂ SO₂]

2. The chlorine atom in chloric acid, HClO₃ [HOClO₂]

3. The oxygen atom in Hydrogen peroxide, HOOH

4. The nitrogen atom in nitric acid, HNO₃ [HONO₂]

5. The oxygen atom in OH group in nitric acid, HNO₃ [HONO₂]

6. The central oxygen atom in the ozone molecule, O₃ 

7. Each of the carbon atoms in the propyne, CH₃ CCH

8. The carbon atom in Freon, CCl₂ F₂

9. each of the carbon atoms in allene H₂CCCH₂

Draw the Lewis structures and predict the shape of each compound or ion:

(a) \({\rm{C}}{{\rm{O}}_{\rm{2}}}\) 

(b) \({\rm{NO}}_{\rm{2}}^{\rm{ - }}\) 

(c) \({\rm{S}}{{\rm{O}}_{\rm{3}}}\) 

(d) \({\rm{S}}{{\rm{O}}_{\rm{3}}}^{{\rm{2 - }}}\)

A molecule with the formula\({\rm{A}}{{\rm{B}}_{\rm{2}}}\), in which A and B represent different atoms, could have one of three different shapes. Sketch and name the three different shapes that this molecule might have. Give an example of a molecule or ion for each shape.

A molecule with the formula\({\rm{A}}{{\rm{B}}_{\rm{3}}}\), in which A and B represent different atoms, could have one of three different shapes. Sketch and name the three different shapes that this molecule might have. Give an example of a molecule or ion that has each shape.

Draw the Lewis electron dot structures for these molecules, including resonance structures where appropriate:

(a) \({\rm{CS}}_{\rm{3}}^{{\rm{2 - }}}\) 

(b) \({\rm{C}}{{\rm{S}}_{\rm{2}}}\) 

(c) \({\rm{CS}}\) 

(d) predict the molecular shapes for \({\rm{C}}{{\rm{S}}_{\rm{3}}}^{{\rm{2 - }}}\) and \({\rm{C}}{{\rm{S}}_{\rm{2}}}\)and explain how you arrived at your predictions

What is the molecular structure of the stable form of \({\rm{FN}}{{\rm{O}}_{\rm{2}}}\) ? (\({\rm{N}}\)is the central atom.)

A compound with a molar mass of about \({\rm{42\;g/mol}}\) contains \({\rm{85}}{\rm{.7\% }}\)carbon and \({\rm{14}}{\rm{.3\% }}\) hydrogen. What is its molecular structure?

The arrangement of atoms in several biologically important molecules is given here. Complete the Lewis structures of these molecules by adding multiple bonds and lone pairs. Do not add any more atoms.

Use the simulation (http://openstaxcollege.org/l/16MolecPolarity) to perform the following exercises for a two-atom molecule: (a) Adjust the electronegativity value so the bond dipole is pointing toward B. Then determine what the electronegativity values must be to switch the dipole so that it points toward A. (b) With a partial positive charge on A, turn on the electric field and describe what happens. (c) With a small partial negative charge on A, turn on the electric field and describe what happens. (d) Reset all, and then with a large partial negative charge on A, turn on the electric field and describe what happens.

Use the simulation (http://openstaxcollege.org/l/16MolecPolarity) to perform the following exercises for a real molecule. You may need to rotate the molecules in three dimensions to see certain dipoles. (a) Sketch the bond dipoles and molecular dipole (if any) for O3. Explain your observations. (b) Look at the bond dipoles for NH3. Use these dipoles to predict whether N or H is more electronegative. (c) Predict whether there should be a molecular dipole for NH3 and, if so, in which direction it will point. Check the molecular dipole box to test your hypothesis.

Use the Molecule Shape simulator (http://openstaxcollege.org/l/16MolecShape) to build a molecule. Starting with the central atom, click on the double bond to add one double bond. Then add one single bond and one lone pair. Rotate the molecule to observe the complete geometry. Name the electron group geometry and molecular structure and predict the bond angle. Then click the check boxes at the bottom and right of the simulator to check your answers.

Use the Molecule Shape simulator (http://openstaxcollege.org/l/16MolecShape) to explore real molecules. On the Real Molecules tab, select H2O. Switch between the “real” and “model” modes. Explain the difference observed.

Use the Molecule Shape simulator (http://openstaxcollege.org/l/16MolecShape) to explore real molecules. On the Real Molecules tab, select “model” mode and S₂O. What is the model bond angle? Explain whether the “real” bond angle should be larger or smaller than the ideal model angle.