Download A Short History of Atomic Models.v2

Aristotle

Lived 384 B.C. to 348 B.C. in
ancient Greece

Proposed matter was made of
4 elements, earth, air, water,
and fire

Each of those were also
described as being a
combination of either cold or
hot and wet or dry

Aristotle also argued that
matter was continuous, and
therefore, could be divided
into smaller parts forever

Aristotle’s authority as a
philosopher gave his theory
dominance for centuries
Democritus

Lived 460 B.C.- 370 B.C.

His theory stated that
matter could be divided
until one arrives at a
smallest, indivisible
piece, called an atomo

Atomos were specific to
different types of matter,
and their shape and size
dictated their function
John Dalton

Lived 1766-1844 in England
His theory stated:

All matter is made of indestructible and
unchangeable atoms

Atoms are hard, round spheres

All atoms of one element are the same,
and different from atoms of other
elements

Compounds are made of different
combinations of atoms in simple whole
number ratios

In a chemical reaction atoms are
rearranged, but never created or
destroyed
J. J. Thompson






Lived 1856-1940
Determined that cathode
ray were made of negatively
charged particles
The same particles were
produced by different gases
Discovered what we now
call electrons!
Proposed the “Plum
Pudding” model of the atom,
where electrons are
imbedded in positively
charged material
Also estimated the charge
to mass ratio of the electron
Cathode Ray Tube Diagram
Rutherford

Lived 1871 -1937

In 1911, he performed
famous “gold foil”
experiment

Alpha particles were shot at
a thin sheet of gold foil

Most particles passed
straight through, but 1 in
8000 were deflected

This lead to the theory that
the atom is mostly empty
space, with a very dense
positive core surrounded by
electrons
Nuclear Model of the Atom
The positively charged
nucleus is very small
and contains most of
the mass of the atom.
The negatively
charged region
around the nucleus
accounts for most of
the atom’s volume.
Henry Mosley

Lived 1887-1915

By using x-ray diffraction and
spectra lines, he determined
the exact atomic number for
some elements

The mathematical relationship
between the spectra lines and
the atomic number is known
as Mosley’s Law

His work also found gaps
where elements should exist,
which were later found

He tragically died in action at
the battle of Gallipoli during
WWI
James Chadwick

Lived 1891-1974

Used certain types of
radioactive decay (similar to a
chain reaction for U-235) to
discover the neutron in 1932

Helped answer the question of
why the atomic mass and the
atomic number are different

This displaced the a theory
that there were extra electrons
in the nucleus that canceled
out the charge of protons
Niels Bohr
Lived 1885-1962
 Developed the Bohr Model of
the atom which explained the
emission spectra of the
hydrogen atom
 The Bohr Model used Maxwell
Planck’s hypothesis that the
energy of an electronic
oscillator is quantized
 In the model, electrons orbit
the nucleus in distinct orbits,
changing orbits by either
receiving or giving off
electromagnetic radiation

Quantum Mechanical Model

A mathematical model called the
Schrodinger Equation treats
electrons as waves with specific
energies

Sometimes called the Electron
Cloud Model, electrons exist in
orbitals which are probable
locations of the electrons around
the nucleus of the atom

An electron’s location is not known
due to Heisenberg's Uncertainty
Principle states that we cannot
measure an electron’s position
and momentum at the same time,
regardless of the tools used.
Sources
























http://www.biography.com/imported/images/Biography/Images/Profiles/D/John-Dalton-9265201-1-402.jpg
http://galileoandeinstein.physics.virginia.edu/lectures/aristot2.html
http://www.webwinds.com/myth/aristotle4elements.gif
http://www.abcte.org/files/previews/chemistry/s1_p1.html
http://www.findabout.net/democritus.html
http://www.iun.edu/~cpanhd/C101webnotes/composition/dalton.html
http://www.biography.com/imported/images/Biography/Images/Profiles/D/John-Dalton-9265201-1-402.jpg
http://ths.talawanda.net/~BrambleN/classroom/Chemistry/Notes/Section%202A/Orbitals.htm
http://library.thinkquest.org/19662/low/eng/model-bohr.html
http://www.cord.edu/faculty/ulnessd/legacy/fall2000/pfeifer/nielsbohr.htm
http://www.aps.org/publications/apsnews/201208/physicshistory.cfm
http://www.sussexvt.k12.de.us/science/The%20Atom/Schr%C3%B6dinger.htm
http://www.nndb.com/people/728/000099431/
http://www.pbs.org/wgbh/aso/databank/entries/dp32ne.html
http://www.iun.edu/~cpanhd/C101webnotes/modern-atomic-theory/rutherford-model.html
http://www.teachnlearnchem.com/JJ%20Thomson.htm
http://www.chemheritage.org/discover/online-resources/chemistry-in-history/themes/atomic-and-nuclearstructure/thomson.aspx
http://www.elmhurst.edu/~chm/vchembook/101Aatoms.html
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&ved=0CEcQFjAD&url=http%3A%2F%2Fwww.sno
w.edu%2Fdanb%2Ffiles%2F1110%2F106%2520develop%2520atomI.ppt&ei=38wCUb_aNtP82gWDlYCIDg&usg=AFQjC
NGBe9UPZctzUSL1Dh3CI5KqFvRsNQ
http://www.chemheritage.org/discover/media/distillations/054-holiday-greetings-2008.aspx
http://ericsaltchemistry.blogspot.com/2010/10/jj-thomsons-experiments-with-cathode.html
http://www.iun.edu/~cpanhd/C101webnotes/modern-atomic-theory/rutherford-model.html
http://tap.iop.org/atoms/rutherford/index.html
http://www.pbs.org/wgbh/aso/databank/entries/dp27un.html