Question

The two most reactive families of elements are the halogens and the alkali metals. How do they differ in their reactivities?

Short answer

The reactivities of halogens and alkali metals differ due to their electronic configurations, ionization energies, and electron affinities. Alkali metals, with an ns^1 configuration, are highly reactive due to their low ionization energies, allowing them to easily lose an electron to achieve stability. Halogens, with an ns^2 np^5 configuration, are highly reactive due to their high electron affinities, allowing them to easily gain an electron for a stable electronic configuration.

Step-by-step solution

Understanding electronic configurations

To understand the reactivities of halogens and alkali metals, we first need to know their electronic configurations. The alkali metals belong to Group 1 in the periodic table and have an ns^1 configuration (where n represents the principal quantum number), meaning they have one electron in their outermost shell. The halogens are in Group 17 and have an ns^2 np^5 configuration, meaning they have seven electrons in their outermost shells.

Explaining reactivity based on electronic configurations

Elements tend to be more reactive when they can easily achieve a stable electronic configuration by losing, gaining, or sharing electrons. For alkali metals, losing one electron results in a stable, noble gas configuration, while for halogens, gaining one electron achieves the same stability. The ease of these processes contributes to their high reactivities.

Analyzing ionization energies

Ionization energy is the energy required to remove an electron from an atom. Alkali metals have low ionization energies as they have only one electron in their outermost shell, which is farther from the nucleus and less attracted to the positive charge. This low ionization energy makes it easier for alkali metals to lose an electron, thus making them highly reactive.

Analyzing electron affinities

Electron affinity is the energy change when an electron is added to an atom. Halogens have a high electron affinity, meaning they easily gain an electron to attain a stable electronic configuration. This high electron affinity, along with their high electronegativity, makes them highly reactive.

Conclusion:

The reactivities of halogens and alkali metals differ due to their electronic configurations, ionization energies, and electron affinities. Alkali metals are highly reactive due to their low ionization energies, allowing them to easily lose an electron to achieve stability. Halogens, on the other hand, are highly reactive due to their high electron affinities, allowing them to easily gain an electron for a stable electronic configuration.