Atomic Theory and Structure
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Greek philosopher that proposed the idea that all matter is made up of atoms
Democritus - 5th Century B.C.
comes from the Greek word “atomos” which means indivisible.
Atom
Since the atom is too small to be seen even with the most powerful microscopes
Scientists’ reliance on models
structure or behavior of atoms cannot be clearly seen
Even the world’s best microscope
British schoolmaster and chemist formulated a precise definition of the indivisible building blocks of matter called “atomos”
John Dalton (18th Century)
composed of extremely small particles
Elements
small particles
atoms
are identical
Atom of elements
is different from the atom of all the other elements
Atom of one element
are composed of atoms of more than one element. The relative number of atoms of each element in a given compound is always the same.
Compounds
only involve the rearrangement of atoms.
Chemical reactions
Atoms are
not created or destroyed in chemical reactions.
The Classical or Dalton’s Atomic Theory
• All matter is made up of tiny, indestructible unit particles called atoms. • The atoms of a given element are all alike. • During chemical reactions, atoms may combine or a combination of atoms may break down, but the atoms themselves are unchanged. • When atoms combine to form molecules, they unite in small whole numbered ratios as 1:1, 1:2, 1:3, 2:
when two elements combine to form more than one compound, the mass of one element, which combines with a fixed mass of the other element, will always be ratios of whole numbers
Law of Multiple Proportions
in a chemical reaction mass is neither created nor destroyed
Law of Conservation of Mass
British scientist who observed many properties of rays, including the fact that the nature of the rays is the same regardless of the identity of the cathode material. He concluded that cathode rays are not waves but are particles with mass and this led to the discovery of electron
Joseph John Thomson ( mid 1800’s)
a pioneer in modern physics, discovered the electron in 1895, revolutionizing existing theories of atomic structure.
SIR JOSEPH JOHN THOMSON
recognized for his investigations into the conduction of electricity through gases and physics
Thomas
which earned him the 1906 Nobel Prize for
Gases (Thomson)
and for his work on the mathematics of the electromagnetic- field theory proposed by James Maxwell.
Physics (Thomson)
measured mass/charge of e-
JJ Thomson (1906 Nobel Prize in Physics)
a specialized vacuum tube in which images are produced when an electron beam strikes a phosphorescent surface
Cathode Ray Tube
positive charge spread over the entire sphere
Thomson’s Model of the Atom
pictured the atom as consisting of small, negatively charged particles of electricity, or electrons, embedded in a heavier, larger sphere of positive electrical charge, like plums in a pudding
Joseph John Thomson (20th Century)