History of the Atomic Theory
Law of Definite Proportions
A given compound contains the same
elements in exactly the same
proportions by mass, regardless of
the size of the sample or the source of
the compound
e.g. NaCl always contains 39.34% by
mass of sodium and 60.66% by mass
of Chlorine
Law of Conservation of Mass
 The
mass of the products of a reaction
equals the mass of the reactants
 e.g.
32 mass units of sulfur and 32 mass
units of oxygen react to form 64 mass
units of sulfur dioxide
Law of Multiple Proportions

The mass ratio for one of the elements that
combines with a fixed mass of another element
can be expressed in small whole numbers

e.g. 2 grams of hydrogen combine with 16
grams of oxygen to form water, but 2 grams of
hydrogen combine with 32 grams of oxygen to
form hydrogen peroxide
16:32 = 1:2
John Dalton
http://www.slcc.edu/schools/hum_sci/physics/whatis/biography/dalton.html
John Dalton’s Billiard Ball Model
http://www.poolndarts.com/index.cfm/fuseaction/Catalog.
Category/categoryID/77.cfm?STLCMPID=1798&engine=adwords!1994&keyword=
%28billiard+ball%29&match_type=
Dalton’s Atomic Theory





1. All matter is made of indivisible and
indestructible atoms.
2. All atoms of a given element are identical in
their physical and chemical properties.
3. Atoms of different elements differ in their
physical and chemical properties.
4. Atoms of different elements combine in
simple whole-number ratios to form compounds.
5. Chemical reactions consist of the
combination, separation, or rearrangement of
atoms.
J. J. Thomson
http://www.aip.org/history/electron/jjhome.htm
Plum Pudding model
http://www.nationmaster.com/encyclopedia/Plum-pudding-model
Ernest Rutherford
http://www.nationmaster.com/encyclopedia/Ernest-Rutherford
Rutherford’s Gold Foil Experiment
Niels Bohr
http://nobelprize.org/physics/laureates/1922/
James Chadwick
http://www.light-science.com/chadwick.html
Model of the Atom
http://www.nationmaster.com/encyclopedia/Image:Atom-diagram.png
Louis deBroglie and Erwin Schrodinger
http://www.britannica.com/nobel/micro/87_61.html
http://www.britannica.com/nobel/micro/531_80.html