Empedocles was the first to suggest that the substances that looked like pure materials were in fact made up of a combination of elements.
Democritus recognized that if you continued to cut a stone into smaller and smaller, at some point you would reach a piece so tiny it could no longer be divided. Democritus called these infinitesimally small pieces atomos. He theorized that atomos were specific to thing that they come from.
Both disagreed with Democritus and as they were very influential at the time Democritus's theory was dismissed. Aristotle went on to say that he agreed with Empedocles's theory and added his own incorrect ideas on to it.
Discovered that air has weight and can push down a column of mercury.
Proposed that air consists of tiny particles that are to small to be seen and are loosely packed in space.
Bolye offered a new definition for an element as a fundamental substance that cannot be broken down further by chemical means.