Bell Work
 On your bell work sheet, date today’s
entry:
1. If a cube has a side length of 2 m, what
is it’s volume in cm3?
2. Using the correct Sig. Figs, evaluate
the following: (36.2-2.1) ÷ 4.2
 Be prepared to take notes
Chapter 3.1 Atomic Philosophy to Theory
Lesson Preview
Lesson Starter
Objectives
Foundations of Atomic Theory
Law of Conservation of Mass
Law of Multiple Proportions
Dalton’s Atomic Theory
Modern Atomic Theory
Objectives
•Explain the law of conservation of
mass, the law of definite proportions,
and the law of multiple proportions.
•Summarize the five essential points of
Dalton’s atomic theory.
•Explain the relationship between
Dalton’s atomic theory and the law of
conservation of mass, the law of
definite proportions, and the law of
multiple proportions.
It Started with the Greeks
DEMOCRITUS
• Lived in Greece 2500
years ago.
• “Father of modern
science”
• He said: “All matter
is made of atoms that
are tiny,
indestructible and
indivisible.”
WHAT DID DEMOCRITUS
PROPOSE ABOUT THE ATOM?
 Atoms are small indestructible, indivisible
particles.
 Made of a single material that’s formed into
different shapes and sizes.
 They are always moving
 They form different materials by joining
together.
(Which of these statements do we now know are correct?
Was Democritus pretty smart for someone who lived
thousands of years ago?)
Democritus
Greek banknote with Democritus and drawing of atom
Where did Democritus get his ideas for
small, indestructible, indivisible
atoms?
Atoms are small…
new wedding rings
old wedding ring
EVIDENCE: Old wedding rings get worn
away slowly, and get thinner and thinner,
but you never see the gold atoms on your
finger, so gold atoms must be very small!
Atoms are indestructible…
EVIDENCE: The Earth has been around a
long time. Even though mountains get
washed away, the rocks continue to
exist. New plants grow where old plants
die.
Atoms are indivisible…
EVIDENCE: None.
This was a HYPOTHESIS made by
Democritus to explain nature as he saw it.
Aristotle had other ideas
Greek banknote and coin picturing Aristotle
ARISTOTLE: Famous Greek philosopher, born 384
BCE. He was a student of Plato (another famous
philosopher) and the teacher of Alexander the
Great, who later conquered the world.
Aristotle’s idea of matter
Aristotle did not believe that
Democritus’s idea of atoms
was correct.
He believed all matter was made
from four elements:
Earth
Air
Fire
Water
Aristotle’s idea of matter
Aristotle was more
famous than Democritus,
so people believed him,
even though he was
wrong.
So Democritus’s idea of
atomos (atoms) was lost
for nearly 2000 years until
John Dalton brought it
back in 1803.
Atom idea lost for ~2000 years
WHAT IS AN ATOM?
 An atom is the
smallest particle of
an element that
retains its
properties.
PIECES OF
CARBON
 For example the
smallest particle of
carbon is a single
atom of carbon. If
you divide it is no
longer carbon
anymore.
CARBON
ATOM
Foundations of Atomic Theory
•The change of 1 or more substances
into one or more new substances is
known as a chemical reaction.
•Law of conservation of mass: mass is
neither created nor destroyed during
ordinary chemical reactions or
physical changes
Conservation of Atoms & Mass
Mass is neither created nor destroyed during physical
or chemical processes.
Fig 2-5
Courtesy Patrick Watson
Foundations of Atomic Theory
•Law of definite proportions: a
chemical compound has the
same elements in exactly the
same proportions.
Foundations of Atomic Theory
•Law of multiple proportions: 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
Law of Multiple Proportions
Law of
Conservation
of Mass
JOHN DALTON
1776-1844
 Two thousand years
later a British chemist
and schoolteacher
brings back
Democritus’s idea of
the atom
 He performed many
experiments to study
how elements join
together to form new
substances
 Created a Theory!
Dalton’s Atomic Theory
1. All matter is composed of extremely
small particles called atoms.
2. Atoms of a given element are identical
in size, mass, and other properties;
atoms of different elements differ in
size, mass, and other properties.
 Atoms of the same element are the
same, different elements are different.
3. Atoms cannot be subdivided, created,
or destroyed.
Dalton’s Atomic Theory,
continued
4. Atoms of different elements combine in
simple whole-number ratios to form
chemical compounds.
 H2O (2:1)
5. In chemical reactions, atoms are
combined, separated, or rearranged.
 2H2O + 2Na  2NaOH + H2
Modern Atomic Theory
• Not all aspects of Dalton’s atomic theory have
proven to be correct. We now know that:
Atoms are divisible into even smaller particles.
A given element can have atoms with different
masses.
• Some important concepts remain unchanged.
All matter is composed of atoms.
Atoms of any one element differ in properties from
atoms of another element.
Reflection (on BW sheet)
1. The fact that every sample of a
particular chemical compound contains the
same elements in exactly the same
proportions by mass is known as the law of
a) conservation of energy.
b) conservation of mass.
c) atomic theory.
d) definite proportions.