Chapter 7: Q101E (page 405)
The molecule XF3 has a dipole moment. Is X boron or phosphorus?
The molecular structure of \({\rm{P}}{{\rm{F}}_{\rm{3}}}\)is not symmetrical and hence dipole does not cancels out.
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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
Determine the formal charge of each element in the following:
(a) \({{\rm{H}}_{\rm{3}}}{{\rm{O}}^{\rm{ + }}}\)
(b) \({\rm{SO}}_{\rm{4}}^{{\rm{2 - }}}\)
(c) \({\rm{N}}{{\rm{H}}_{\rm{3}}}\)
(d) \({\rm{O}}_{\rm{2}}^{{\rm{2 - }}}\)
(e) \({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}\)
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?
Question: Using the standard enthalpy of formation data in Appendix G, show how the standard enthalpy of formation of \({\rm{HCl(g)}}\) can be used to determine the bond energy.
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.
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