Atomic Theory

History of Atom Early Greeks believed that matter consisted

of tiny particles – they called the “atoms”

John Dalton English school teacher in 1800’s Proposed atomic theory

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 Conservation of Mass Matter and its mass cannot be created or

destroyed

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

Law of Multiple Proportions Two or more different compounds are

composed of the same 2 elements, they are whole number ratios of each other