Why are ideas on the nature of matter different from those held 200 years ago, and different from those held 2500 years ago?
Because science has progressively advanced, and new discoveries lead to new definitions and new qualifications.
Greek philosophers held that matter was composed of small indivisible species, each called an
As a point of interest, historically, electrons were conceived to have a negative charge, and the protons in the atomic nucleus were assigned a positive charge. If we were doing this over again, electrons would be assigned a positive charge - it would save generations of students trying to solve quantum equations who got the answer wrong because they wrongly counted an odd number of electrons and got a