What is the difference between a stable and unstable element

Stable elements are those that are unlikely to react with other elements, and unstable are those that are highly reactive. Stable elements are the noble gases (full outer shell - won't bond with others). The unstable elements should be the ones in Group 1 and Group 7 because they bond together easily since they have a "desire" to fill their outer shell.

Stable elements are those that are unlikely to react with other elements and unstable are those that are highly reactive.