Transcript Atomic Theory

Atomic Theory
History of Atom
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Early Greeks believed that matter consisted
of tiny particles – they called the “atoms”
John Dalton
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English school teacher in 1800’s
Proposed atomic theory
Dalton’s Atomic Theory
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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
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Atoms can combine in simple, wholenumber ratios to form compounds
In chemical reactions, atoms can combine,
separate, or rearrange
Dalton’s Theory Today
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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
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Matter and its mass cannot be created or
destroyed
Law of Definite Composition
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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
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Two or more different compounds are
composed of the same 2 elements, they are
whole number ratios of each other