Download Section 2.1

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 17th 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