2.1: Atoms - Ideas from the Ancient Greeks All matter in the universe is made out of tiny building blocks called atoms. All modern scientists accept the concept of the atom, but when the concept of the atom was first proposed about 2,500 years ago, ancient philosophers laughed at the idea. It has always been difficult to convince people of the existence of things that are too small to see. We will spend some time considering the evidence (observations) that convince scientists of the existence of atoms. 2.2: Scientific Laws - Conservation of Mass and Definite Proportions This section continues the discussion of the historical development of the concept of the atom with the works of Lavoisier and Proust which resulted to the law of conservation of mass and the law of definite proportions. 2.3: John Dalton and the Atomic Theory of Matter 2.4: The Mole and Molar Mass 2.5: Mendeleev and Periodic Table 2.6: Atoms and Molecules- Real and Relevant Thumbnail: Spinning Buckminsterfullerene (\(\ce{C60}\)). (CC BY-SA 3.0; unported; Sponk ).