The scientific concept developed by Democritus was the atomism.

Here's a breakdown:

* Democritus was an ancient Greek philosopher who lived around 460-370 BC.

* Atomism is the philosophical idea that all matter is composed of physically indivisible particles called atoms.

While Democritus's ideas were groundbreaking, they were based on philosophical reasoning rather than scientific experimentation. It wasn't until the 19th century that the atomic theory was scientifically established by scientists like John Dalton.