Download The Birth of Atomic Theory

The Birth of Atomic Theory
What is an atom like?
What are atoms like?
• Atomic theory
– A theory about what atoms are like
– Scientific theories
• The best explanation possible using what the
information that is known. Theories can be
updated if new information is discovered.
• Many scientists have made Atomic
Theories over the years…
Democritus- the Greek Philosopher
(~400 B.C.)
• Said the universe is made of super
small particles called atoms
• Said atoms cannot be divided into
smaller parts
• Movements of atoms cause all
changes we can see
John Dalton, the English chemist
(1808 A.D.)
• All matter is made of atoms, which
cannot be divided.
• Atoms of the same element are exactly
the same
• Atoms of different elements can join to
form molecules.
• A chemical reaction is a rearrangement
of atoms.
J.J. Thomson
(1891)
• Used cathode ray tubes to discover
the electron.
• An electron’s mass is 1,836 times
smaller than a proton
• Proved atoms are made up of smaller
parts.
• Created the “plum pudding” model of
the atom.
Ernest Rutherford
(1911)
• The gold foil experiment
showed the Plum Pudding
model was incorrect.
• Rutherford discovered the
nucleus
Niels Bohr, the Danish scientist
(1913)
• Said there are different energy levels
that describe how far an electron is
from the nucleus
• The further away from the nucleus,
the higher the energy level.
• Electrons can only orbit in certain
locations.
Schrödinger’s Model
(1926)
• Electrons do not move around the
nucleus like planets around the sun
• The exact location of electrons cannot
be determined
• Electrons are found in orbitals, or
locations where they are most likely
to be.
Image Sources
• Crookes tube- two views
– by D.Kuru via Wikimedia Commons
• J.J. Thomson portrait
– via Wikimedia Commons
• Plum pudding
– by Musical Linguist via Wikimedia Commons
• blueberry muffin
– by mars! via Flickr
• Plum pudding atom
– by FastFission via Wikimedia Commons
• Ernest Rutherford (Nobel)
– via Wikimedia Commons
• Rutherford atom
– by cburnett via Wikimedia Commons
• Orbital | 3, 2, 0 >
– via The Physics Hypertextbook