The atomic theory was and is one of the greatest contributions of the Greek philosophers. Let us read to find out what contributions were added to it's development by Islam.
To begin with the origin of the atomic theory is traceable to 400 B.C in the Greek philosopher Leucippus who believed in the existence of two realities, namely what is (Atom) and what is not (empty space or void). He reasoned that if you take any material and keep on dividing it by cutting it into smaller pieces, a point would be reached when that smallest bit could not be further broken down into anything much smaller. To this insignificant part he gave the name of atomos, meaning that which is uncuttable from which derives the word atom. From this he proposed his atomic theory which states that matter is composed of these fundamental particles that cannot be further divided. Further, Leucippus believed that any property observed about any matter resulted from the movement and collisions of these atoms in empty space. He also believed that the behaviour of atoms were predetermined and not by chance. Leucippus was a pupil of the Greek philosopher Zeno of Elea.
But then it was Democritus (460-370 BC), a pupil of Leucippus, another philosopher, who developed fully the atomic theory. He argued that the material world consisted of an infinite number of atoms moving in empty space. These atoms were distinguishable from each other in shape, size and position. Everything observed in the world is the result of different combinations of atoms. From these infinite number of atoms and through different combinations have also come into existence other worlds. Sensation resulted from collisions of these atoms with our sense organs. Democritus was born in Abdera in Northern Greece and wrote on ethics, physics, mathematics, literature and language.
After Leucippus and Democritus nothing significant was added to the atomic theory. Epicurus, another Greek philosopher, was responsible for incorporating the atomic theory by Democritus into his philosophical works.
Similarly, the Roman poet and philosopher Lucretius preserved atomism (name given to atomic theory) in his long poems; thereby transmitting its knowledge to latter generations. After that period was revealed the holy Quran to the Prophet Mohammed, on whom be peace, in which the word atom (Zarra in Arabic) was stated. The Quran revealed crucial and important properties about the atom including the weight of the atom (Mithqaal Zarra), destructibility of the atom into sub-atomic particles, its combination into molecules and most significantly the existence of positive and negative particles associated with the atom. All these have been treated in previous publications of the Times. These disclosures in the Quran coupled with what they inherited from the Greeks spurred Muslims into research on the atom, thereby paving way to further discoveries. In science as a whole one of the greatest contributions made by the Islamic philosophers, whom I call scientists, was the experimental method. In the field of atomic theory Greeks made indelible contributions but were wholly speculative and lacked experimental results and data to support their theories. On the contrary Muslims philosophers, mostly interested in measurements, introduced the experimental method to serve as the hard line of demarcation between science and philosophy.
Before preceding any further let me pass the following comment concerning the Quranic association of weight with the infinitesimally small and invisible atom. The Greeks were mostly right in conceiving the atom as a point in empty space through whose combinations materials resulted, in reference to chemical reactions. An examination of their theories, however, discloses that the idea of such an atom having weight never occurred to them. In contrast the holy Quran mentions the atom associated with the word weight in four separate verses (Quran 99:8, Quran 99:9, Quran 10:62, Quran 34:4). From Quran 98:8 we read: "Then whoso does an atom's weight of good will see it". Thus in four separate versus the Quran mentions atom (Zarra) accompanied by weight (Mithqaal) to prove positively and most convincingly that the atom too has weight. It was not until the advent of the 20th century when scientists succeeded in measuring the weight of this minutest particle as 1.623 multiplied by ten raised to the negative power twenty seven.
On the Muslim perception of the atom we read the following views: "Although initially, Islamic scientific theories were basically Greek, the Muslims did make major contributions. Their philosophers were deeply interested in matter, motion, space and time and were well aware of the views of Democritus which they modified significantly. To Democritus the properties of matter were those of the constituent atoms. Copper was red, for example, because each copper atom was red. But to the great Islamic thinkers, the properties of matter resulted from the way atoms combined. Copper was red because of the way atoms were arranged in a piece of copper (This belief was perhaps the first glimmering that observable properties depend on the arrangement of atoms). The conflict between the viewpoint of the Muslim atomists and that of Democritus was settled in the mid-nineteenth century. Some Arab philosophers, as reported by the medieval Jewish scholar Maimonides, believed that not only matter but space, time and motion were discontinuous, a startling modern idea (HUGH W. Salzberg, from Caveman to Chemist, American Chemical Society, Washington, 1991,p59).
Continuing we need: "During the middle ages the atomic theory was largely ignored since Aristotle, another great ancient Greek Philosopher, had rejected it. Aristotle's theories on philosophy and science dominated medieval science, even though his views were largely wrong. Take for example his views on chemical combinations in which he viewed the combining atoms as losing their individual identities in the resulting compound. This was contradicted by Avicenna (Ibn Sina) (980-1037AD) who considered that chemicals maintain their identities even in compounds" (Hugh W.Salzberg, from Caveman to Chemist, American Chemical Society, Washington, 1991, p64)
The Greeks take credit for formulating the atomic theory. The Muslims take the credits for correcting and modifying it to modern standards.