Download Chapter 4 “Atomic Structure” Section 4.1 Defining the Atom

Chapter 4
“Atomic Structure”
Section 4.1 Defining the Atom
 OBJECTIVES:
Democritus’s ideas
about atoms.
Describe
Section 4.1 Defining the Atom
 OBJECTIVES:
Explain
theory.
Dalton’s atomic
Ancient Philosophy
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Who: Aristotle, Democritus
When: More than 2000 years ago
Where: Greece
What: Aristotle believed in 4 elements: Earth, Air,
Fire, and Water. Democritus believed that matter
was made of small particles he named “atoms”.
Why: Aristotle and Democritus used observation
and inference to explain the existence of
everything.
Section 4.1 Defining the Atom

The Greek philosopher Democritus (460
B.C. – 370 B.C.) was among the first to
suggest the existence of atoms (from
the Greek word “atomos”)
 He
believed that atoms were indivisible and
indestructible
 His ideas did agree with later scientific
theory, but did not explain chemical
behavior, and was not based on the
scientific method – but just philosophy
Democritus
Aristotle
Alchemists
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Who: European Scientists
When: 800 – 900 years ago
Where: Europe
What: Their work developed into what is now
modern chemistry.
Why: Trying to change ordinary materials into gold.
Alchemic Symbols
Particle Theory
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Who: John Dalton
When: 1808
Where: England
What: Described atoms as tiny particles that could
not be divided. Thought each element was made
of its own kind of atom.
Why: Building on the ideas of Democritus in
ancient Greece.
John Dalton
Particle (Atomic) Theory
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1. All elements are composed of tiny indivisible
particles called atoms
2. Atoms of same elements are identical. Atoms from
one element are different from atoms of a different
element.
3. Atoms of different elements can physically mix
together or can be chemically combine to form
compounds.
4. Chemical reactions occur when atoms are
separated, joined, or rearranged. However, atoms of
an element never changes into atoms of another
element as a result of the chemical reaction.
(p102 textbook)
Sizing up the Atom
 Elements are able to be subdivided into
smaller and smaller particles – these are
the atoms, and they still have properties
of that element
If you could line up 100,000,000
copper atoms in a single file, they
would be approximately 1 cm long
Despite their small size, individual
atoms are observable with instruments
such as scanning tunneling (electron)
microscopes