Bell-Ringer


How have your ideas about Santa Claus and
the Easter Bunny changed as you have
grown up?
Is it important to keep an open mind when it
comes to new ideas in science?
Chapter 3:
Atoms: The Building Blocks of
Matter
Coach Kelsoe
Chemistry
Pages 66–88
Section 3-1
The Atom: From Philosophical
Idea to Scientific Theory
Coach Kelsoe
Chemistry
Pages 66–71
The Atom
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Around 400 B.C.,
Democritus gave the
atom its name, based on
the Greek word meaning
indivisible.
“A” means not, and
“tomos” means “cutting.”
Aristotle did not believe in
atoms.
Democritus
Foundations of the Atomic Theory


In the 1790s, the law of
conservation of mass
was formulated.
The law of conservation
of mass states that mass
is neither created nor
destroyed during ordinary
chemical reactions or
physical changes.
Created
Destroyed
Law Of Conservation of Mass
+

=
Carbon Oxygen
Mass x Mass y
=
CO
Mass x + y
+
CO
Carbon
Mass x + y Mass x
Oxygen
Mass y
The number of carbon
atoms and the number
of oxygen atoms are the
same before and after
each reaction!
Foundations of the Atomic Theory

The law of definite
proportions states that a
chemical compound
contains the same
elements in exactly the
same proportions by
mass, regardless of the
size of the sample or
source of the compound.
Foundations of the Atomic Theory

The law of multiple
proportions states that if two
or more different compounds
are composed of the same two
elements, then the ratio of the
masses of the second element
combined with a certain mass
of the first element is always a
ratio of small whole numbers.
Carbon Monoxide
1 C: 1 gram
1 O: 1.33 grams
Carbon Dioxide
1 C: 1 gram
2 O: 2.66 grams
Dalton’s Atomic Theory

John Dalton’s theory explained the previous laws.
His theory said:
1.
2.
3.
4.
5.
All matter is composed of atoms.
Atoms of a given element are identical in size, mass,
and other properties, and atoms of different elements
differ in size, mass, and properties.
Atoms can not be subdivided, created, or destroyed.
Atoms of different elements combine in simple, wholenumber ratios to form chemical compound.
In chemical reactions, atoms are combined, separated,
or rearranged.
Modern Atomic Theory

Not all aspects of Dalton’s Atomic Theory
are correct.



We know that atoms are divisible.
We know that elements can have atoms with
different masses.
The important concepts are that all matter
is composed of atoms, and that atoms of
any one element differ in properties from
atoms of another element.