Can we believe in atoms and molecules ? I heard that Ibn Taymiyah (rahimahullah) rejected atoms (i.e .did not believe in it). Is this true?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

The terms "molecules" and "atoms", as per the contemporary recognized physics terminology, were not used at the time of Shaykh Ibn Taymiyyah. We know nothing of his statements that implies his denial of the fact that the matter is made up of molecules, which are, in turn, made up of atoms. Rather, it is reported on his authority that he denied the infinite divisibility of matter and the existence of the "smallest indivisible particle" (Al-Jawhar Al-Fard).

It should be noted that investigating such topics is of no benefit for common Muslims; therefore, they should not be preoccupied with them. The scholars who discussed them only did that for the sake of refuting the advocates of religious innovations and those who follow personal inclinations.

Allah Knows best.