Atomic Theory
History of Atom Early Greeks believed that matter consisted
of tiny particles – they called the “atoms”
Dalton’s Atomic Theory All matter is composed of tiny particles
called atoms Atoms of a given element have the same
size, mass, and physical properties Atoms cannot be subdivided, created, or
destroyed
Atoms can combine in simple, whole-number ratios to form compounds
In chemical reactions, atoms can combine, separate, or rearrange
Dalton’s Theory Today Dalton’s theory still holds true today with a
few exceptions Atoms can be subdivided in nuclear
reactions Atoms of he same element can have
different masses – they are called Isotopes
Law of Definite Composition In a compound, the ratio of atoms is always
the same For example:
water (H2O) always has a mass ratio of 1:8
In water there is always 1 gram of water for 8 grams of oxygen