Questions: Skill #3 - Electron Affinity, Multiple Choice Which of the following gas phase reactions will produce a positive electron affinity? I. O(g) + e^- -> O^-(g) II. Mg(g) + e^- -> Mg^-(g) III. Ar(g) + e^- -> Br(g) IV. F(g) + e^- -> F^-(g) V. S(g) + e^- -> S^-(g) A. I, IV and V B. III only C. II and III D. I and IV

Skill #3 - Electron Affinity, Multiple Choice
Which of the following gas phase reactions will produce a positive electron affinity?
I. O(g) + e^- -> O^-(g)
II. Mg(g) + e^- -> Mg^-(g)
III. Ar(g) + e^- -> Br(g)
IV. F(g) + e^- -> F^-(g)
V. S(g) + e^- -> S^-(g)
A. I, IV and V
B. III only
C. II and III
D. I and IV

Transcript text: Skill #3 - Electron Affinity, Multiple Choice Which of the following gas phase reactions will produce a positive electron affinity? I. $\mathrm{O}_{(\mathrm{g})}+\mathrm{e}^{-} \rightarrow \mathrm{O}^{-}$ (g) II. $\mathrm{Mg}_{(\mathrm{g})}+\mathrm{e}^{-} \rightarrow \mathrm{Mg}_{(\mathrm{g})}^{-}$ III. $\mathrm{Ar}_{(\mathrm{g})}+\mathrm{e}^{-} \rightarrow \mathrm{Br}_{(\mathrm{g})}$ IV. $F_{(g)}+e^{-} \rightarrow F^{-}(g)$ V. $\mathrm{S}_{(\mathrm{g})}+\mathrm{e}^{-} \rightarrow \mathrm{S}_{(\mathrm{g})}^{-}$ A. I, IV and V B. III only C. II and III D. I and IV

Solution

Solution Steps

Step 1: Understanding Electron Affinity

Electron affinity is the energy change that occurs when an electron is added to a neutral atom in the gas phase to form a negative ion. A positive electron affinity means that energy is released when the electron is added.

Step 2: Analyzing Each Reaction

Reaction I: $ O_{(g)} + e^- \rightarrow O^-_{(g)} $ Oxygen has a high electron affinity because it is highly electronegative and readily accepts an electron.
Reaction II: $ Mg_{(g)} + e^- \rightarrow Mg^-_{(g)} $ Magnesium, being an alkaline earth metal, has a low electron affinity because it prefers to lose electrons rather than gain them.
Reaction III: $ Ar_{(g)} + e^- \rightarrow Ar^-_{(g)} $ Argon is a noble gas with a complete valence shell, so it has a very low electron affinity.
Reaction IV: $ F_{(g)} + e^- \rightarrow F^-_{(g)} $ Fluorine has a very high electron affinity because it is highly electronegative and readily accepts an electron.
Reaction V: $ S_{(g)} + e^- \rightarrow S^-_{(g)} $ Sulfur has a relatively high electron affinity, though not as high as oxygen or fluorine, it still releases energy when gaining an electron.