Early Atomic Theory
Chemistry MYP
Ms. Khan
Early Greek Atomism
Early Greek Atomism
DEMOCRITUS
PLATO
▪ early 5th century BCE
▪ mid – late 5th century BCE
▪ proposed that everything is
composed of atoms and
empty void
▪ believed the world was
created
from
four
“elements”
– air, earth, fire, water
▪ “atom” comes from Greek
word “atomos”, meaning
“indivisible”
Early Greek Atomism
ARISTOTLE
ACCEPTED IDEA
▪ approximately 330 BCE
▪ all philosophers’ ideas were
considered speculation
▪ argued that the “elements”
were not made of atoms
▪ change happened through
transformation instead of
rearrangement
▪ no experimental evidence
to support either Democritus
or Aristotle
▪ Aristotle’s idea more widely
accepted though
Early Modern Atomic Theory
Early Modern Atomic Theory
LAW OF CONSERVATION OF
MASS, 1789
LAW OF DEFINITE PROPORTIONS,
1799
▪ mass is neither destroyed nor
created
during
ordinary
chemical reactions or physical
changes
▪ 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
▪ total mass of reactants and
products in a chemical reaction
remains constant
▪ formulated by Antoine Lavoisier
▪ proven by Joseph Louis Proust
Early Modern Atomic Theory
LAW OF MULTIPLE
PROPORTIONS, 1808
▪ 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
the first element is always a
ratio of small whole numbers
▪ proposed by John Dalton
▪ used the laws of conservation of
mass and definite proportions to
establish law of multiple
proportions
▪ used the three laws to form
Dalton’s Atomic 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
3. atoms cannot be subdivided, created, or destroyed
4. atoms of different elements combine in simple whole-number ratios to
form chemical compounds
5. in chemical reactions, atoms are combined, separated, or rearranged
Consider the following… (to turn in)
1. How do the postulates of Dalton’s atomic theory relate to
the three laws (law of conservation of mass, law of definite
proportions, law of multiple proportions)?
2. How do the postulates relate to the ideas of the Greek
philosophers?
3. Which of the postulates are known to be true today? Which
are known to be false today? What information do you
know that makes them false?
Here you go…
teehee.