Chapter 2 1 The Atomic Theory of Matter

Chapter 2. 1 The Atomic Theory of Matter

The History of the Atom • Greek philosophers in 450 BC • Atomos- invisible particles • Plato and Aristotle • No invisible matter • Europeans in 17 th century • Reemergence of the atoms as gas particles

John Dalton • 1803 • English school teacher that linked idea of elements to atoms

Dalton’s Atomic Theory • Each element is composed of extremely small particles called atoms • All atoms of a given element are identical to one another in mass and other properties, but atoms of an element are unique to that element only. • Atoms of an element are not changed into atoms of a different element by chemical reactions; they are neither created nor destroyed. • Compounds are formed when atoms of more than one element combine, a given compound always has the same relative number and kind of atoms.

Atom • Smallest particle of an element that retains the chemical identity of the element.

Law of Constant Composition • In a given compound, the relative number and kind of atoms are constant.

Law of Conservation of Matter • Total mass of materials present after a chemical reaction is the same as the total mass present before the reaction.

Law of Multiple Proportions • If two elements A and B combine to form more than one compound, the masses of B that combine with a given mass of A are in the ratio of small whole numbers