What is an Atom
 Atoms are the building blocks that
make everything we see, touch, eat,
hear or smell (humans, chairs, pencils,
apples, ect)
 It made of 3 different parts, the
electron, the proton, and the neutron.
 The proton and the neutron are
attached to each other making the
nucleus which is the center of the
atom.
 The electron is a tiny negatively
charged particle that is much, much
smaller than any atom. It circulates
the nucleus.
Democritus
 In 400 BC a Greek philosopher ,Democritus, stated that all
matter is made up of atoms. He also stated that atoms are
eternal and invisible and so small that they can’t be divided,
and they entirely fill up the space they are in.
 He named them “atomos” meaning indivisible in Greek.
John Dalton
 In the 19th century John Dalton came up with
an atomic theory that linked to his
experiments and observations.
 This is a summary of the atomic theory.
 All matter is made of atoms. Atoms are
indivisible and indestructible.
 All atoms of a given element are identical in
mass and properties.
 Compounds are formed by a combination of
two or more different kinds of atoms.
 A chemical reaction is a rearrangement of
atoms.
 Atoms can be neither created nor destroyed.
J.J Thomson
 In 1897 J.J Thomson changed the view of an
atom by discovering the electron. He
discovered it while doing an experiment by
applying high voltages to gases at low
pressure.
 Some experiments showed that it would take
about 2000 electrons to weigh the same as
the lightest atom, hydrogen.
 Since they were so small Thomson suggested
that they could only have come from inside
atoms. So Dalton's idea of the indestructible
atom is not fully true.

He said that the tiny negatively charged
electrons must be inside a pool of positive
charge. He called this the plum pudding.
Ernest Rutherford
 Ernest Rutherford found out that the positive charge must be
in a small value in the center of the atom and that the electron
orbits around the nucleus.
 He found this out while doing an experiment with radiation.
 He came up with a new model and it was different from
Thomson’s model.
Niels Bohr
 Niels Bohr stated that the electron orbits the nucleus without
losing energy and that they only move in fixed orbits of specific
energies.
 He also said that electrons with low energy would orbit closer
to the nucleus while electrons with high energy orbit further
from the nucleus. He came up with a new atomic model.
Bibliography

"History of the Atom." History of the Atom. N.p., n.d. Web. 13 Oct. 2012.
<http://web.neo.edu/rjones/Pages/1014new/Lecture/chemistry/chapter_8/pages/hist
ory_of_atom.html>.

"Chemistry Project :Â The History Of The Atom." Chemistry Project :Â The History Of
The Atom. N.p., n.d. Web. 13 Oct. 2012. <http://hi.fi.tripod.com/timeline/>.

"History of the Atom." History of the Atom. N.p., n.d. Web. 13 Oct. 2012.
<http://www.absorblearning.com/chemistry/demo/units/LR301.html>.

"HISTORY OF THE ATOM FROM DEMOCRITUS TO BOHR AND
SCHRÖDINGER." HISTORY OF THE ATOM FROM DEMOCRITUS TO BOHR AND
SCHRÖDINGER. N.p., n.d. Web. 13 Oct. 2012.
<http://profmokeur.ca/chemistry/history_of_the_atom.htm>.

"Science Is Easier than It Sounds." : What Are Atoms Made Of? N.p., n.d. Web. 13 Oct.
2012. <http://science-is-easy.blogspot.com/2009/11/what-are-atoms-made-of.html>.