One distinguishing property of the alkali metals is that they are highly reactive.

Here's why:

* Low ionization energy: They easily lose their single valence electron, making them strong reducing agents.

* Large atomic radius: Their outer electron is relatively far from the nucleus, making it easy to remove.

This high reactivity makes alkali metals useful in various applications, but also requires careful handling as they react vigorously with air, water, and many other substances.