Question

The changes in electron affinity as one goes down a group in the periodic table are not nearly as large as the variations in ionization energies. Why?

Short answer

The changes in electron affinity as one goes down a group in the periodic table are not nearly as large as the variations in ionization energies because, although both quantities are influenced by atomic size and electron shielding, the effects are more significant for ionization energy. As atomic size increases and electron shielding becomes more pronounced, the force binding the outer electrons to the nucleus significantly decreases, making it easier to remove them. In comparison, the incoming electron for electron affinity still experiences some attraction to the nucleus despite electron shielding, resulting in less significant changes.

Step-by-step solution

Understanding Electron Affinity and Ionization Energy

Electron affinity is the energy change associated with the addition of an electron to a gaseous atom. It represents the attraction between the incoming electron and the positively charged nucleus. Ionization energy, on the other hand, is the energy required to remove an electron from a gaseous atom. It represents the strength of the attraction between the electron and the nucleus.

Factors influencing electron affinity and ionization energy

As we go down a group in the periodic table, two primary factors influence electron affinity and ionization energy: atomic size and electron shielding. 1. Atomic size: As we go down a group, atomic size increases due to the addition of energy levels. This means that the outermost electrons are farther from the nucleus and are held less tightly. This results in a decrease in ionization energy. 2. Electron shielding: The increased number of energy levels also results in greater electron shielding, which is the repulsive force between the inner and outer electrons. This shielding reduces the effective nuclear charge experienced by the outer electrons, further decreasing ionization energy.

Comparison between electron affinity and ionization energy changes

Both electron affinity and ionization energy are influenced by atomic size and electron shielding. However, the effect on ionization energy is more pronounced because the increase in atomic size and shielding significantly reduces the force that binds the outer electrons to the nucleus, making it easier to remove them. In contrast, the changes in electron affinity are less significant because the added electron is still attracted to the positively charged nucleus. Although the electron shielding reduces the effective nuclear charge, the incoming electron still experiences some attractive force, so the changes are not as large as in ionization energy.

Conclusion

The changes in electron affinity as one goes down a group in the periodic table are not as large as the variations in ionization energies because the factors influencing both quantities (atomic size and electron shielding) have a more significant effect on ionization energy, making the changes in electron affinity less pronounced.