An element that is, sadly, no longer in existence.

A pair of closely related elements which only honest chemists can separate.

A substance that is very rarely available, as you can't get the wood, you know.

Useful element in most experiments. When treated with care, will remind you of the date of the experiment, set up the lab beforehand and write up the notes afterwards. Can get overexcited. Occasionally becomes unstable. [Projoy] Top notch.

An element often inherited from a parent's spinster sister.