Atomic theory began as an ancient philosophy dating back to at least the fifth and sixth centuries BCE in both Greece and India. In fact, the word atom is taken from the Greek word “atomos,” meaning indivisible . The term atom was used to define the basic particle that made up a chemical element. Chemists during the time of the ancient Greeks believed that atoms were the fundamental particles of matter. In other words, the atom was thought to be the smallest possible unit that matter could be broken down into. This basic philosophy proposed that a solid object could potentially be divided again and again, until it eventually reached the smallest indivisible unit—an atom. Based on the prefix in- , what does the word indivisible Mean?