Which correctly summarizes the trend in electron affinity? It tends to be very high for Group 2. It tends to be more negative across a period. It tends to remain the same across periods. It tends to be more negative down a group.
The Correct Answer and Explanation is:
Correct Answer: It tends to be more negative across a period.
Explanation
Electron affinity refers to the amount of energy released (or sometimes absorbed) when an atom in the gaseous state gains an electron to form a negative ion. A more negative electron affinity means that the atom more readily accepts an electron, releasing more energy in the process.
The trend in electron affinity across a period (left to right on the periodic table) generally becomes more negative. This is because atoms have increasing nuclear charge (more protons in the nucleus), which leads to a stronger attraction between the nucleus and any added electrons. As a result, elements on the right side of the periodic table, particularly the halogens in Group 17, have highly negative electron affinities. For example, chlorine has one of the most negative electron affinities because it is just one electron away from a full octet and readily gains an electron to become stable.
In contrast, moving down a group (top to bottom), electron affinity tends to become less negative. This is because the added electron is farther from the nucleus due to increased atomic size and shielding from inner electrons. The attraction between the nucleus and the incoming electron is weaker, so less energy is released. For instance, fluorine has a more negative electron affinity than iodine.
It is not correct to say electron affinity is high for Group 2 elements (alkaline earth metals), as these elements have filled s-orbitals and are relatively stable. They do not easily gain electrons, and their electron affinities are low or even slightly positive.
Similarly, it’s incorrect to say electron affinity remains the same across a period—it varies significantly due to changing nuclear charge and electron configurations.
Thus, the most accurate summary is: Electron affinity tends to become more negative across a period.
