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History of the Atom

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Ann Blalock

on 18 November 2016

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Transcript of History of the Atom

Chapter 4
Hisory of the Atom
The Beginning of the Atom
Today's Model
of the Atom
Democritus- (460-370 B.C.)
atoms are indivisible and indestructible
no experimental support and not useful in explaining chemical behavior

Aristotle- (384 B.C)
Did not agree with Democritus
He said all matter is uniform throughout and not composed of smaller particles
Developed Dalton's Atomic Theory
This theory was based on Democritus' ideas of the atom and included 4 main points
John Dalton
Discovered the first of the subatomic particles the electron
The first model of a divisible atom
Called the Plum Pudding model
Atoms consist of a large sphere of uniform positive charge embedded with smaller negatively charged particles
J.J. Thompson (1897)
Ernest Rutherford (1911)
The atom its self is neutral, meaning that the number of positive charges equals the number of negative charges.
Chocolate chip cookie dough is today's equivalent of plum pudding.
Very small positively charged area called the nucleus containing most of the mass of the atom.
Very large volume called the electron cloud contained negatively charged particles.
Credited with the discovery of protons (+)
the second of the subatomic particles discovered
James Chadwick
Discovered the neutron in 1932
Studied under Ernest Rutherford
Know for his work on the Manhattan Project
4 Points of
Dalton's Atomic Theory
1. All elements are composed of tiny indivisible 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

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 element as a result of a chemical reaction.

Robert A. Millikan
Did Experiments to determine the mass of electrons
Determined the mass of one negatively charged electron is 1/1840 the mass of a hydrogen atom
Really Really Small!!!
Rutherford and others realized quickly that there were particles besides protons in the nucleus but could not prove it... unitl...
Niels Bohr's Model of Atom (1912)

RULE 1: Electrons can orbit only at certain allowed distances from the nucleus.
RULE 2: Atoms radiate energy when an electron jumps from a higher-energy orbit to a lower-energy orbit. Also, an atom absorbs energy when an electron gets boosted from a low-energy orbit to a high-energy orbit.
Erwin Schrodinger’s Model (1926)
We cannot determine exactly where an electron is at any point in time
with probability calculations you can determine where they might be
electron cloud model
Eugene Goldstein (1866)
Discovered the proton
Write each scientists name what what they discovered regarding the atom.

- Draw a picture of their model of the atom if they had one.
Full transcript