Chapter 15, Problem 18STP

Interpretation Introduction

Interpretation: The pair which is most likely to form an ionic bond is to be determined.

Concept introduction: The bond which has maximum electronegativity difference is most likely to form an ionic bond. The electronegativity of the bond is calculated by taking the difference of electro negativity of the elements forming the bond.

  $\begin{array}{l}{\text{χ}}_{\text{A}-\text{B}}={\text{χ}}_{\text{A}}-{\text{χ}}_{\text{B}}\end{array}$

  $\begin{array}{c}\text{w}\text{h}\text{e}\text{r}\text{e}{\text{χ}}_{\text{A}}\text{i}\text{s}\text{g}\text{r}\text{e}\text{a}\text{t}\text{e}\text{r}\text{t}\text{h}\text{a}\text{n}{\text{χ}}_{\text{B}}\end{array}$

Answer to Problem 18STP

D

Explanation of Solution

For each bond, the difference in electronegativity is calculated as follows:

$\begin{array}{l}{\text{χ}}_{\text{C}-\text{S}}={\text{χ}}_{\text{S}}-{\text{χ}}_{\text{C}}\end{array}$

  $\begin{array}{c}=2.6-2.6\end{array}$

  $\begin{array}{c}=0\end{array}$

$\begin{array}{c}{\text{χ}}_{\text{A}\text{l}-\text{M}\text{g}}={\text{χ}}_{\text{A}\text{l}}-{\text{χ}}_{\text{M}\text{g}}\end{array}$

   $\begin{array}{c}=1.6-1.3\end{array}$

   $\begin{array}{c}=0.3\end{array}$

$\begin{array}{c}{\text{χ}}_{\text{C}\text{u}-\text{S}}={\text{χ}}_{\text{S}}-{\text{χ}}_{\text{C}\text{u}}\end{array}$

   $\begin{array}{c}=2.6-1.9\end{array}$

   $\begin{array}{c}=0.7\end{array}$

$\begin{array}{c}{\text{χ}}_{\text{M}\text{g}-\text{F}}={\text{χ}}_{\text{F}}-{\text{χ}}_{\text{M}\text{g}}\end{array}$

   $\begin{array}{c}=4-1.3\end{array}$

   $\begin{array}{c}=3.7\end{array}$

$\begin{array}{c}{\text{χ}}_{\text{A}\text{l}-\text{C}}={\text{χ}}_{\text{C}}-{\text{χ}}_{\text{A}\text{l}}\end{array}$

   $\begin{array}{c}=2.6-1.6\end{array}$

   $\begin{array}{c}=1.0\end{array}$

Therefore, Mg-F bond is most electronegative and most likely to form ionic bond.

Conclusion

Calculations show that option D is correct. Thus, other options are wrong.