Download Section 1 Slides - St. John`s College HS

Chapter 4; Section 1
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Describe Democritus’s ideas about atoms.
Explain Dalton’s atomic theory
Understand that special instruments are
necessary to observe individual atoms.
John Dalton
• John Dalton (1766-1814)
• Dalton took Democritus’s ideas and
made it scientific theory
Early Atoms
• Atom: The smallest particle of an element that
retains the idenity in a chemical reaction.
• Democritus’s (460 -370 ) Atomic Philosophy:
• First to suggest the existence of atoms
• However his suggestion lacked experimental
B.C.
B.C.
evidence, and did not explain chemical
behavior.
Dalton’s Atomic Theory
1.All elements are composed of tiny invisible particles
called atoms
2.Atoms of the same element are identical. The atoms of
any one element are different from those of any other
element
Atoms cannot be subdivided, created, or destoryed.
Atoms of different elements can physically mix together
or can chemically combine in simple whole-number ratios
to form compounds.
Chemical reactions occur when atoms are separated,
joined, or rearranged. Atoms of one element, however, are
never changed into atoms of another elements.
3.
4.
5.
Size of an Atom
• 2.4 x 10
• 7 x 10
9
22
copper atoms in one coin
live on the Earth
• Atoms can be seen with
instruments such as scanning
tunneling microscopes.
Current Atomic Theory
1. All elements are composed of tiny invisible particles
called atoms. Atoms can be broken down into even
smaller, more fundamental particles.
2. Atoms of the same element are identical. The atoms of
any one element are different from those of any other
element
3. Atoms of different elements can physically mix together
or can chemically combine in simple whole-number ratios
to form compounds.
4. Chemical reactions occur when atoms are separated,
joined, or rearranged. Atoms of one element, however, are
never changed into atoms of another elements as a result
of a chemical reaction.