What term describes a substance that is made when two or more different atoms bond together in a certain ratio?

A Molecule should be it because it is a bond between atoms to make for instance diamonds.

☆ionisation energy increases across a period from na -> ar☆ionisation energy decreases down a group from li -> fr☆ionic radius decreases across a period from na -> cl☆ionic radius increases down a groupfrom f -> ii hope it clarifies your doubts