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, wholenumber 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
Compound Name
Compound Symbol
Carbon Monoxide
CO
Carbon Dioxide
CO2
Which of the following is not
part of Dalton’s Atomic Theory
A)
B)
C)
D)
Matter is made of atoms
Atoms can be subdivided
Atoms combine or separate in
chemical reactions
Atoms cannot be created or destroyed
In water, the mass ratio of hydrogen
to oxygen is 1:8. If you have 10
grams of hydrogen in a sample of
water, how many grams of oxygen is
there
A)
B)
C)
D)
16
32
80
800
In a chemical reaction 15 g of A combine with
30 g of B to form compound AB. What is
the mass of AB?
If the mass ratio is 3:2 in compound AB, what
is the ratio is compound AB2? 3:___