Question

a. What is electron affinity? b. What signs are associated with electron affinity values, and what is the significance of each sign?

Short answer

Electron affinity is the energy change when an atom gains an electron. Negative values mean energy is released and the process is favorable, while positive values mean energy is required and the process is unfavorable.

Step-by-step solution

- Define Electron Affinity

Electron affinity is the amount of energy released when an atom in the gaseous state accepts an electron to form an anion.

- Meaning of the Sign of Electron Affinity

The sign of electron affinity can be either positive or negative. A negative electron affinity value means that energy is released when the atom gains an electron, which is common for most nonmetals. A positive electron affinity value means that energy must be added for the atom to gain an electron, which is less common.

- Significance of Negative Electron Affinity

Negative electron affinity values indicate that the addition of an electron is a favorable process and the atom becomes more stable after gaining an electron.

- Significance of Positive Electron Affinity

Positive electron affinity values indicate that the addition of an electron is unfavorable and requires energy input, implying that the atom is less stable after gaining an electron.

Key concepts

Energy Release

Electron affinity refers to the energy change when an atom gains an electron.
When we say energy is released, it signifies that the process is exothermic.
Most nonmetals release energy when they gain an electron since they reach a more stable state.
This release of energy can be represented as a negative value in electron affinity measurements.
For example, when a chlorine atom gains an electron, it releases energy, reaching a more stable configuration.

Anion Formation

During anion formation, an atom gains an extra electron.
When an atom in a gaseous state traps an electron, it becomes negatively charged, forming an anion.
This process is associated with electron affinity values.
Elements with high electron affinities are more likely to form anions because the process releases energy and increases stability.
For instance, fluorine easily gains an electron to form a fluoride anion, releasing energy in the process.

Gaseous State

Electron affinity measurements are conducted with atoms in the gaseous state.
In this state, atoms are isolated, free from interactions with other atoms or molecules.
This isolation allows us to accurately measure the energy change when an electron is added.
For instance, the electron affinity of chlorine is measured when chlorine exists as individual gaseous atoms, not in any bonded or liquid form.

Negative Electron Affinity

A negative electron affinity value means energy is released when an atom gains an electron.
This release signifies that the process is favorable and results in a more stable anion.
Most nonmetal atoms, such as oxygen and sulfur, have negative electron affinity values.
These atoms readily accept an electron, releasing energy and stabilizing themselves.

Positive Electron Affinity

A positive electron affinity value indicates energy input is required for an atom to gain an electron.
This requirement signifies that the process is unfavorable and results in a less stable anion.
Metals often have positive electron affinities, meaning they resist gaining electrons.
For instance, noble gases have positive electron affinity values due to their stable electron configurations that do not favor additional electrons.