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Chapter 8: Problem 140

Although both \(\mathrm{Br}_{3}^{-}\) and \(\mathrm{I}_{3}^{-}\) ions are known, the \(\mathrm{F}_{3}-\) ion has not been observed. Explain.

Short Answer

Expert verified
The \(\mathrm{F}_{3}^-\) ion does not exist due to the high electronegativity of fluorine (F), which makes it difficult for it to gain an extra electron needed to form the ion. In contrast, the lower electronegativities of bromine (Br) and iodine (I) allow them to form stable \(\mathrm{Br}_{3}^-\) and \(\mathrm{I}_{3}^-\) ions.

Step by step solution

01

Understand electronegativity and stability of ions

Electronegativity is the measure of an atom's ability to attract shared electrons in a chemical bond. A high electronegative element tends to attract electrons more easily, making it less likely to form negative ions with additional electrons. Fluorine (F) is the most electronegative element, while iodine (I) and bromine (Br) have lower electronegativities.
02

Compare electronegativities of F, Br, and I

We can look up the electronegativity values of F, Br, and I on a periodic table or in a reference book: - Fluorine (F): 3.98 - Bromine (Br): 2.96 - Iodine (I): 2.66 As we can see, the electronegativity of F is significantly higher than those of Br and I, meaning it is more likely to attract electrons rather than giving up or accepting additional ones.
03

Relate the electron configurations

Each of the elements in the F, Br, and I triatomic ions has 7 valence electrons. In the case of the \(\mathrm{Br}_{3}^-\) and \(\mathrm{I}_{3}^-\) ions, these elements form a covalent bond with two other like atoms, creating a total of 6 shared electrons and one free electron. The extra free electron makes these ions negatively charged. In the case of the F atom, however, its high electronegativity makes it difficult to gain an extra electron needed to form the \(\mathrm{F}_{3}^-\) ion. This makes the formation of \(\mathrm{F}_{3}^-\) ion energetically unfavorable and unstable.
04

Conclusion

Although the \(\mathrm{Br}_{3}^-\) and \(\mathrm{I}_{3}^-\) ions are known and stable due to their lower electronegativity values, the \(\mathrm{F}_{3}^-\) ion is not observed because of the high electronegativity of the F atom. The F atom's strong tendency to attract electrons makes it difficult to gain an extra electron, which would be needed to form a stable \(\mathrm{F}_{3}^-\) ion.

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Most popular questions from this chapter

Use the following standard enthalpies of formation to estimate the \(\mathrm{N}-\mathrm{H}\) bond energy in ammonia: $\mathrm{N}(g), 472.7 \mathrm{kJ} / \mathrm{mol} ; \mathrm{H}(g),\( \)216.0 \mathrm{kJ} / \mathrm{mol} ; \mathrm{NH}_{3}(g),-46.1 \mathrm{kJ} / \mathrm{mol}$ . Compare your value to the one in Table \(8.5 .\)

For each of the following, write an equation that corresponds to the energy given. a. lattice energy of \(\mathrm{NaCl}\) b. lattice energy of \(\mathrm{NH}_{4} \mathrm{Br}\) c. lattice energy of \(\mathrm{MgS}\) d. \(\mathrm{O}=\mathrm{O}\) double bond energy beginning with \(\mathrm{O}_{2}(g)\) as a reactant

Consider the following reaction: $$A_{2}+B_{2} \longrightarrow 2 A B \quad \Delta H=-285 \mathrm{kJ}$$ The bond energy for \(\mathrm{A}_{2}\) is one-half the amount of the AB bond energy. The bond energy of \(\mathrm{B}_{2}=432 \mathrm{kJ} / \mathrm{mol}\) . What is the bond energy of \(\mathrm{A}_{2}\) ?

Oxidation of the cyanide ion produces the stable cyanate ion, \(\mathrm{OCN}^{-}\) . The fulminate ion, \(\mathrm{CNO}^{-}\), on the other hand, is very unstable. Fulminate salts explode when struck; \(\mathrm{Hg}(\mathrm{CNO})_{2}\) is used in blasting caps. Write the Lewis structures and assign formal charges for the cyanate and fulminate ions. Why is the fulminate ion so unstable? (C is the central atom in \(\mathrm{OCN}^{-}\) and \(\mathrm{N}\) is the central atom in \(\mathrm{CNO}^{-}\) )

Think of forming an ionic compound as three steps (this is a simplification, as with all models): (1) removing an electron from the metal; (2) adding an electron to the nonmetal; and (3) allowing the metal cation and nonmetal anion to come together. a. What is the sign of the energy change for each of these three processes? b. In general, what is the sign of the sum of the first two processes? Use examples to support your answer. c. What must be the sign of the sum of the three processes? d. Given your answer to part c, why do ionic bonds occur? e. Given your above explanations, why is NaCl stable but not $\mathrm{Na}_{2} \mathrm{Cl} ? \mathrm{NaCl}_{2} ?$ What about MgO compared to \(\mathrm{MgO}_{2} ? \mathrm{Mg}_{2} \mathrm{O} ?\)
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