Transcript Early Models of the Atom - Santa Susana High School

EARLY MODELS OF THE ATOM
Objectives:
 1. Define the term atom.
 2. List the postulates of Dalton's atomic theory.
Key Terms:
 Atom, law of constant position, atomic theory of
matter
ATOMS - A BRIEF HISTORY
Atoms are the smallest particle of an element
retaining all of its properties. Though, invisible to
the eye and microscope (limited images are possible
with the tunneling microscope), you could theorize
that an atom of gold would have the same luster
and texture (look and feel) as a solid gold bar. The
belief in atoms as the basic building block of matter
dates back o the Greek philosophers (450 BC) when
Democritus first proposed the existence of atomos
(small particles of matter). Unfortunately
Democritus' views were not accepted until the early
1700s.
ATOMIC THEORY - TIMELINE
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1700 - Lavoisier - The Law of Conservation of matter Matter can not be created nor destroyed.
1799 - Proust - Law of Constant Composition - Given
compounds always contain the same proportion
(ratios) of elements.
1803 - Dalton - Atomic Theory of Matter
Elements are composed of atoms (Smallest particle
retaining the identity of the element)
 Atoms in an element are identical but different from other
elements
 Atoms can be joined or separated in chemical reactions but
cannot be altered to form different atoms
 Atoms can be mixed or chemically combined to form
compounds that always have the same ratios and kinds of
atoms
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ATOMIC THEORY – TIMELINE (PART 2)
Late 1800s - Henri Becquerel accidentally
discovers radioactivity (emission of particles from
the nucleus an the atom)
 1897 - J.J. Thompson used a CRT to discover the
moving part of an atom was negatively charged
 1916 - Robert Millikan determines the size and
charge of an electron
 Early 1900s - Ernest Rutherford aims an alpha
beam at gold foil to determine the arrangement
of subatomic particles
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