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Lesson3_Theory of Atomic Structure Models.pptx
1. IDEAS OF THE ANCIENT GREEKS ON THE ATOM
• The idea of the atomic model started from early Greek concept of the
atom. Greek philosophers and thinkers were the first to describe matter
and to wonder whether matter could be divided infinitely into smaller
pieces or if there was a limit to the number of times a piece of matter
could be divided.
• Democritus, a Greek Philosopher who, after much observation and
thoughtful questioning, concluded that matter could not be divided into
smaller and smaller pieces infinitely. He called this indivisible smallest
possible piece of matter an atom.
• The term atom comes from the Greek word, atomos which means
indivisible or cannot be divided. The philosophers who shared the of
Democritus about the atom were called atomists.
2. CONTRIBUTIONS OF JOHN DALTON TOWARD THE
UNDERSTAND OF THE CONCEPTS OF CHEMICAL
ELEMENTS
• John Dalton, an English teacher and scientist proposed an atomic theory
about the indivisible building blocks of matter called atoms. His
hypotheses which state in part that the atoms were responsible for the
formation of compounds by combining two or more elements can be
summarized as follows:
• 1. All elements of matter are composed of extremely small particles called
atoms.
• 2. Atoms of the same element are identical, having the same size, mass and
chemical properties. Atoms of one element are different from atoms of
another element.
3. CONTRIBUTIONS OF JOHN DALTON TOWARD THE
UNDERSTAND OF THE CONCEPTS OF CHEMICAL
ELEMENTS
• 4. A chemical reaction involves only the separation, combination or
rearrangement of atoms. It does not result in their creation or destruction.
This is the “Law of Conservation of Mass” which states that matter can be
neither created nor destroyed.
Atomic Theory Proposed by John Dalton
1. Atoms are indivisible particles and all elements are composed of atoms.
2. Same elements have exactly alike atoms.
3. While atoms of same elements are the same, atoms of different elements
are different.
4. ATOMIC THEORY PROPOSED BY JOHN DALTON
• 4. Two or more atoms of same elements can be combined to form
compounds. They combine I fixed ratios of whole numbers forming
particles of molecules.
• 5. Atoms are units of chemical change which involves combinations
or rearrangements of atoms where they are not created.
