History of Atom

History of the Atom
Scientists and Their Contribution to
the Model of an Atom
Democritus
(460 BC – 370 BC)
•  Proposed a theory of
ATOMISM which states:
–  Atoms are particles in space and make
up everything
–  Atoms are in constant motion
–  Atoms are indivisible
–  Things differ in the universe because
of shape, arrangement and position of
atoms
–  Every event results from a collision of
atoms which make life predictable
•  Aristotle did not support
his atomic theory
Image taken from:
https://reichchemistry.wikispaces.com/T.+Glenn
+Time+Line+Project
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Aristotle
(350 BC)
•  Rejected atomism
•  Aristotle modified an earlier
theory that matter was made of
four “elements”: earth, fire,
water, air
•  Matter was continuous and not
made of individual smaller
particles
Aristotle
fire
earth
air
water
Antoine Lavoisier
(1743 – 1794)
Image taken from:
www.ldeo.columbia.edu/.../v1001/
geotime2.html
•  Known as the “Father of
Modern Chemistry”
•  Discovered/proposed that
combustion occurs when
oxygen combines with other
elements
•  Discovered/proposed the
Law of Conservation of
Mass (or Matter) which
states, in a chemical
reaction, matter is neither
created nor destroyed
•  Thought matter is concrete
and measureable
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John Dalton
(1766 – 1844)
•  First Modern Atomic Theory called
Chemical Atomic Theory or Billiard Ball
Model
a.  Elements of matter consist of characteristic
kinds of particles b.  These particles of an element are identical to
each other c.  Atoms are indivisible d.  There are as many kinds of atoms as there
are elements e.  Atoms of one element can’t be converted into
another f.  Atoms in chemical reactions are neither
created or destroyed; merely rearranged g.  Law of multiple proportions which describes
how atoms combine to make different
compounds
•  Calculated the atomic weights of many
various elements
Image taken from:
chemistry.about.com/.../JohnDalton.htm
J.J. Thomson
(1856 – 1940)
Image taken from:
www.wired.com/.../news/2008/04/
dayintech_0430
•  Proved that an atom can be
divided into smaller parts
•  While experimenting with
cathode-ray tubes, discovered
corpuscles, which were later
called electrons
•  Stated that the atom is neutral
•  In 1897, proposed the Plum
Pudding Model which states that
atoms mostly consist of
positively charged material with
negatively charged particles
(electrons) located throughout
the positive material
•  Won a Nobel Prize
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Ernest Rutherford
(1871 – 1937)
•  In 1909, performed the
Gold Foil Experiment and suggested
the following characteristics of the
atom:
o  Consists of a small core, or nucleus, that
contains most of the mass of the atom
o  Nucleus is made up of particles called
protons, which have a positive charge
o  Protons are surrounded by negatively
charged electrons, but most of the atom
is actually empty space
•  Did extensive work on radioactivity
(alpha & beta particles, gamma rays/
waves) and was referred to as the
“Father of Nuclear Physics”
•  His model is often called “Nuclear
Model”
Image taken from:
http://www.scientific-web.com/en/
Physics/Biographies/
ErnestRutherford.html
Ernest Rutherford (movie1, movie2)
•  Rutherford shot alpha (α) particles at gold foil.
Zinc sulfide screen
Lead block
Radioactive
substance
Thin gold foil
path of invisible
α-particles
Most particles passed through.
So, atoms are mostly empty.
Some positive α-particles
deflected or bounced back!
Thus, a “nucleus” is positive &
holds most of an atom’s mass.
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Niels Bohr
(1885 – 1962)
Image taken from:
commons.wikimedia.org/wiki/
File:Niels_Bohr.jpg
•  In 1913, proposed the Bohr
Model, which suggests that
electrons travel around the
nucleus of an atom in orbits or
definite paths.
•  Additionally, the
electrons can jump from a path
in one level to a path in another
level (depending on their energy)
•  Won a Nobel Prize
•  Worked with Ernest Rutherford
Erwin Schrodinger
(1887-1961)
•  In 1926, further explained the
nature of electrons in an atom by
stating exact location of an
electron cannot be determined
•  It is more accurate to view the
electrons in regions called electron
clouds;
•  electron clouds are places where
the electrons are likely to be
found
•  Did extensive work on the Wave
formula à Schrodinger equation
•  Won a Nobel Prize
Image taken from:
nobelprize.org/.../1933/
schrodinger-bio.html
5
James Chadwick
(1891 – 1974)
Image taken from:
www.wired.com/.../news/2009/02/
dayintech_0227
•  Realized that the atomic
mass of most elements was
double the number of
protons à discovery of the
neutron in 1932
•  Worked on the Manhattan
Project
•  Worked with Ernest
Rutherford
•  Won a Nobel Prize
Heisenberg
•  Came up with the Heisenberg Uncertainty
Principle
•  It states that you can’t know BOTH the
momentum and position of an electron at
the same time
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History of the Atom - Timeline
Antoine Lavoisier
Thomson
makesJ.J.
a substantial
the
number discovers
of contributions
electron
and
to the
field of
proposes the
Chemistry
Plum Pudding
Model 1871
in 1897
– 1937
1766 – 1844
Niels Bohr
proposes
the Bohr
Model in
1913
1887 – 1961
James
Chadwick
discovered
the neutron
in in 1932
1700s
1800s
1900s
460 – 370 BC
0
Democritus
proposes
the 1st atomic
theory
Erwin
John Dalton
Ernest Rutherford
Schrodinger
proposesperforms
his
the Gold Foil
describes
1891 – 1974
atomic theory
Experiment
in
in 1909
the electron
1803
cloud in 1926
1743 – 1794
1885 – 1962
1856 – 1940
Click on picture for more information
Progression of the Atomic Model
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The structure of an atom, according to:
Electron Cloud
Democritus
James
Ernest
Erwin
Neils
Schrodinger
Chadwick
Rutherford
Bohr&
J.J.
Thomson
John Dalton
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