Which correctly summarizes the trend in electron affinity?
A. t tends to be very high for group
B. It tends to be more negative across a period.
C. It tends to remain the same across periods.
D. It tends to be more negative down a group?
The Correct Answer and Explanation is:
The correct answer is B. It tends to be more negative across a period.
Explanation:
Electron affinity refers to the energy change that occurs when an electron is added to a neutral atom in the gas phase. More negative electron affinity means the atom releases energy when it gains an electron, indicating a greater tendency to accept an electron. The trend in electron affinity across a period and down a group is influenced by atomic structure, particularly the number of protons in the nucleus and the distance of the valence electrons from the nucleus.
Across a Period:
As you move from left to right across a period on the periodic table, the nuclear charge (number of protons) increases. This stronger positive charge in the nucleus pulls electrons more tightly, making it easier for the atom to attract additional electrons. Consequently, the electron affinity becomes more negative (energy is released more effectively when an electron is added) across a period, although there are exceptions due to the electron configuration of certain elements. For example, noble gases have very low (or positive) electron affinities because their valence shells are full, making them less likely to accept an electron. In general, however, elements in the middle of the period (like halogens) have very negative electron affinities due to their desire to complete their valence electron shells.
Down a Group:
As you move down a group in the periodic table, electron affinity becomes less negative. This happens because the added electron is farther from the nucleus, due to the increasing number of electron shells. The shielding effect (where inner electrons block the attraction of the nucleus) increases, reducing the nucleus’ ability to attract the added electron. Therefore, while the electron affinity is still negative, it is less negative down a group.
Other options:
- A. Electron affinity is not particularly high for any specific group; it is more negative for nonmetals like halogens.
- C. Electron affinity does not remain the same across a period; it generally becomes more negative.
- D. Electron affinity is less negative down a group, not more negative.
Thus, the correct answer is B, as electron affinity tends to become more negative across a period.