What is the basic form of matter which cannot be broken down any further?

atom The atom is the smallest. most basic form of matter that retains it's unique characteristics. The first person to come up with the idea of an atom is the greek Democritus who lived from 460 BC to 370 BC. We currently know of 115 elements, of which 90 are naturally occurring (atomic numbers from 1-92 excluding 43 and 61). Mankind has managed to obtain or synthesize all elements with atomic numbers from 1 to 112, plus 114, 116, and 118.

The density would be 1.622