The Atomic Model

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Transcript The Atomic Model

The Atomic Model
Chem 9
The Greek Model
• Democritus - A Greek Philosopher, 400 BC.
• Concluded that matter could not be
divided into smaller and smaller pieces
• Eventually, the smallest piece of matter
would be found.
• He used the word "Atomos“ meaning
The Dalton Model: Billiard Ball Model
John Dalton - The English chemist that proposed
first Atomic Theory in 1803.
All elements are composed of indivisible particles.
Atoms of the same element are exactly alike.
Atoms of different elements are different.
Compounds are formed by joining atoms of two or more
The Thomson Model:
Chocolate Chip Cookie Model
Plum Pudding Model
J. J. Thomson 1856 – 1940 – (English scientist)
• discovered negative particle (an Electron) in 1887
by using a cathode ray tube
• initially called electrons CORPUSLES
Robert A. Millikan
(1868 – 1953)
1900 – mass of Electron
approximately 1/2000 the
mass of a Hydrogen atom
1916 -determined the charge
carried by an electron
Eugene Goldstein
(1850 -1930)
• 1866 Eugene Goldstein found
Positive particle – Protons
• He named them CANAL RAYS
Sir James Chadwick 1891 - 1974
– Discovered
the neutron in 1932
– Has no charge
– Neutron’s mass is
close to proton’s
Ernest Rutherford - British Physicist
Gold Foil Experiment
In 1908, proved the atom had a small,
dense, positively charged Nucleus.
He said an atom is mostly empty space and
negative electrons are scattered around
the outside edge.
Niels Bohr (Danish scientist)
The Planetary Model - 1913
Bohr proposed:
• Electrons move in definite orbits
around the nucleus, like planets
moving around the sun.
• That each electron moves in a
specific energy level.
Quantum Mechanical Model
 Erwin Schrodinger (1887-1961)
 -Electrons have NO definite path in an atom.
 -Only a probable location is known based
 on how much energy it has.
-Atomic orbitals (s,p,d,f) are NOT fixed paths as
Bohr suggested
• Dalton : Solid Sphere
• Thomson : Pos. & neg mixed together
• Rutherford: Positive nucleus, neg
electrons surrounding it
• Bohr: Positive nucleus, neg electrons in
exact orbits
• Quantum Mechanical Theory
– (Electron cloud theory)