Transcript History of the Atom and Periodic Table

History of the Atom and
Periodic Table
Democritus and Aristotle
 Around 400 B. C., Democritus claimed all matter was
made of tiny, indivisible particles called “atoms”.
 Aristotle disagreed and claimed matter was made of
earth, wind, water, and fire.
Dmitri Mendeleev
 Mendeleev was responsible for creating the 1st
periodic table. Elements were arranged by atomic
mass.
Henry Moseley
 Henry Moseley created the Modern Periodic Table of
Elements that we use today. It is arranged by atomic
number rather than mass.
John Dalton
 In the early 1800s, Dalton created his atomic theory
about matter.
J. J. Thomson
 Thomson discovered the first subatomic particle
called the electron.
 Electrons are negatively charged and orbit the
nucleus.
 He later discovered a subatomic, positively charged
particle in the nucleus called the proton.
Ernest Rutherford
 Rutherford realized that atoms had a nucleus in the
center that is orbited by electrons. Between the two
is a lot of empty space.
Niels Bohr
 Bohr expanding on the atomic model by placing
electrons on separate energy levels.
James Chadwick
 Chadwick discovered the last subatomic particle that
had a neutral charge and it is called the neutron.
 His discovery made us realize isotopes existed.
 Isotopes are atoms of the same element with a
different number of neutrons.
 Proved Dalton’s Atomic theory was incorrect again by
showing atoms of the same element can be different.