As you move from left to right across a period in the periodic table, how do electron affinity values typically change?

As you move from left to right across a period in the periodic table, electron affinity values typically increase. This trend occurs due to the increasing nuclear charge that results from additional protons in the nucleus. As the effective nuclear charge increases, atoms have a stronger attraction for electrons. Consequently, the energy released when an electron is added to an atom—the definition of electron affinity—increases.

For example, elements on the left side of a period, such as alkali metals, have a relatively low electron affinity as they are more inclined to lose an electron than gain one. In contrast, elements on the right side of a period, particularly the halogens, have a high electron affinity because they are more energetically favoring acquiring an electron to achieve a full valence shell, leading to a more stable electron configuration.

This increasing trend is consistent across most periods in the periodic table, making it a reliable rule of thumb for understanding the behavior of elements as one moves from left to right.