Question

The process requiring absorption of energy is (1) \(\mathrm{F} \rightarrow \mathrm{F}^{-}\) (2) \(\mathrm{H} \rightarrow \mathrm{H}^{-}\) (3) \(\mathrm{Cl} \rightarrow \mathrm{Cl}^{-}\) (4) \(0 \rightarrow O^{2-}\)

Short answer

\(O \rightarrow O^{2-}\)

Step-by-step solution

Understand the Process

We need to determine which of the given processes require the absorption of energy. This means we are looking for processes that are endothermic.

Define Electron Affinity

Electron affinity is the amount of energy released when an electron is added to a neutral atom in the gaseous state. Most elements release energy (exothermic) when gaining an electron to form a negative ion.

Compare Options

Consider each of the given processes: (1) \ \ \(\text{F} \rightarrow \text{F}^{-}\)\ (2) \ \ \(\text{H} \rightarrow \text{H}^{-}\)\ (3) \ \ \(\text{Cl} \rightarrow \text{Cl}^{-}\)\ (4) \ \ \(\text{O} \rightarrow \text{O}^{2-}\).\

Evaluate Each Process

1. \(\text{F} \rightarrow \text{F}^{-}\) releases energy because it is exothermic.

Conclusion

The most significant energy-absorbing process is \(O \rightarrow O^{2-}\).

Key concepts

Electron Affinity

Electron affinity refers to the amount of energy released when an electron is added to a neutral atom in the gaseous state. This process usually releases energy, making it exothermic. For example, if you add an electron to a fluorine (F) atom, it becomes a fluoride ion (F⁻), and energy is released. This released energy suggests that the atom readily accepts the electron, which is common for elements like fluorine and chlorine.
However, understanding electron affinity helps us identify whether a process will absorb or release energy when forming negative ions. Not all processes are exothermic; some require energy absorption, making them endothermic.

Energy Absorption

Energy absorption occurs when a process requires added energy for completion. In the context of forming negative ions, energy absorption implies that the atom does not easily accept the additional electrons. This is often the case with atoms needing more than one additional electron to reach a stable state. For instance, converting an oxygen (O) atom into an oxide ion (O²⁻) requires adding two electrons.
This process demands more energy input than simpler processes. The extra electrons added to the O atom repel each other, making the entire process energetically unfavorable. Hence, converting O to O²⁻ is endothermic because it absorbs energy.

Negative Ion Formation

Negative ion formation involves an atom gaining one or more electrons. When atoms accept electrons, they become negatively charged ions. Many elements easily form negative ions by gaining a single electron, releasing energy in the process. However, when forming ions that require gaining multiple electrons, the process may become energy-intensive. For example, hydrogen (H) forms a hydride ion (H⁻) by gaining one electron, releasing a small amount of energy. Likewise, chlorine (Cl) forms a chloride ion (Cl⁻) similarly.
In contrast, forming ions like O²⁻ from oxygen involves complex interactions due to adding more electrons than usual, causing energy absorption. This complexity underscores the importance of understanding which processes are energetically favorable and which are not, helping students discern between endothermic and exothermic processes.