Download History of Atomic Models Greek Model 450 B.C. Dalton`s Atomic

History of Atomic Models
Most of atomic model evolution was based on indirect evidence.
Greek Model ­ 450 B.C.
• Democritus asked "can you split matter indefinitely (forever)."
• He said NO.
• Called the smallest part of matter an ATOM.
Dalton's Atomic Model ­ 1806
• Based on observations about gases that he published in the "Theory of the Atom"
• All elements are composed of atoms.
• Atoms are indivisible and indestructible.
• Atoms of the same element are exactly alike.
• Atoms of different elements are different.
• Compounds are formed by the joining of atoms of two or more elements.
Thomson's Atomic Model ­ 1897
• Based on experiments on the passage of electric current through gas.
• Atoms are made of a pudding­like positively charged material with negatively charged corpusuls (electrons) throughout.
• Proposed the existence of particles smaller than an atom (subatomic particles).
Rutherford's Atomic Model ­ 1908
• Based on experiments involving firing tiny streams of positively charged particles (bullets) through gold foil.
• Dense nucleus (center) surrounded by scattered electrons (negative charge).
• Proposed a positively charged center called a nucleus.
Bohr's Atomic Model
• Based on observations and experiments using the Rutherford model.
• Electrons orbit in energy levels
• Proposed that electrons are found in specific energy levels located at specific distances away from the nucleus.
Modern Atomic Model ­ Current
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Based on the principles of wave mechanics.
Can not determine the exact location of any one electron.
Can predict general location of electrons based on energy.
Atoms have enough electrons to make the atom neutral.