The concept of the atom was first proposed roughly two thousand years ago by the Greek philosopher Democritus. He argued that matter was finite and comprised of particles that are indivisible. Like all the philosophers of his time, Democritus based his argument on reason, not experimental data. In more recent years, the composition of matter has been studied further, and only within the last century was it determined that the atom is indeed divisible. Today, scientists believe that even some subatomic particles can theoretically be divided even further. The figure above illustrates our modern model of the atom. At the center is a nucleus containing protons and neutrons. Around the nucleus are much lighter particles called electrons. The atom is largely comprised of empty space. Can you think of how we might go about studying the behavior of matter at the atomic and subatomic level? How do you suppose we might study aspects of matter that cannot be directly observed? These are the questions that philosophers and scientists have pondered for millennia. We will address some of these questions as we attempt to further understand the particles that make up matter.
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