Question

What is the difference between a stable and unstable element

Answer 1

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

Answer 2

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.