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The History of the Atom

From Democritus to Murray Gell-Mann Chapter 4 Sixth Grade Science

Cindy Mullikin

on 29 March 2017

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Transcript of The History of the Atom

The History of the Atom
Sir Joseph
John Thomson
Sir Joseph
John Thomson

Niels Bohr
Sir Ernest Rutherford
Sir James

Atomic Theory (Circa 400 BC)
Democritus assumed that some kind of small, particle structure existed. He believed that this structure was
to the human eye, and was, and always will be
. He is credited for defining the word ‘

Democritus was known as "The Laughing Philosopher" because he was often cheerful while at work.
Conservation of Mass (late 18th century-1700s)
Lavoisier is remembered for conducting multiple experiments that determined conservation of mass. He proved that mass cannot be created or destroyed.

During his lifetime, Lavoisier also identifying
elements. He is famous for his attention to detail and precise measurement. This was a great contribution, for it paved the road for a new way to do science. He took credit for discovering the formula for water, but many believe he stole this from his friend, Joseph Priestley.

Known as "
The Father of Modern Chemistry
" and was unfortunately beheaded during the French Revolution in 1794. The charge against him: watering down tobacco!

Dalton's Atomic Theory (Circa 1803)
The idea of the atom was uncertain until Dalton solidified its
existence as a fundamental object of chemistry.
His theory is composed of 4 well known points:

1) All
is made of atoms. Atoms are
and indestructible.

2) All atoms of a given element are
and properties

are formed by a combination of two or more different kinds of atoms.

4) A chemical
is a rearrangement of atoms.

Although the first two points have been proven to be wrong, Dalton’s Atomic Theory is still important and significant today.

Inspiring: John Dalton was from a poor Quaker family and he was colorblind. He began teaching school at the age of 12. He did not allow his personal challenges keep him from being successful. As a Quaker, Dalton led a modest existence, although he received many honors later in life. In Manchester more than 40,000 people marched in his funeral procession.
Periodic Table (1869)
Mendeleev used the atomic mass of the
known elements at the time, to organize them into a sort of map we know today as the Periodic Table of Elements. He also managed to arrange these elements by similarity of their properties. He published his Periodic Table in Principles of Chemistry in 1869.

Ray Experiment (1893)
Plum Pudding Model (1904)
The Modern Atom Model (1913)
Gold Foil
Experiment (1910)

Discovered Neutron ( 1935 )
Using a cathode ray, J.J. Thomson discovered the existence of the electron. He shot rays through the tube and discovered, using magnetic fields, that negative charges existed within the ray.
Using the deflection angles of the particles when influenced by positive and negative magnetic fields, Thomson was able to calculate the electric charge of an electron.
J.J. Thomson believed that because of an electron’s negative charge, the atom must be balanced by some sort of positive charge.
Because the charge and mass in an atom was unknown at the time, Thomson presented the Plum Pudding Model, a diagram depicting positive and
negative charges filling
a sphere
Here is a plum pudding model of an atom.
Niels Bohr questioned the plum pudding model. Bohr proposed a model of the atom in which
electrons orbited
the nucleus rather than occupy the nucleus like in the plum pudding model.He worked on the Manhattan Project.
was a student of JJ Thomson. He is best known for his "Gold Foil Experiment". It was through this experiment that the
was discovered. Did you know that his original hypothesis was wrong? Remember right or wrong is not the question......you just want to show what you know... Rutherford surely did this!

James Chadwick was a student of Ernest Rutherford. He was successful in discovering the
. Now our "model" of an atom had a nucleus made of positive protons together with neutral neutrons. Each has a mass of one. When you count the number of protons and the number of neutrons you get the "
atomic mass
He worked on the Manhattan Project.

From Democritus to Murray Gell-Mann
400 BC to Today


Used quantum mechanics in discovering the building blocks of neutrons and protons....
. There are six types of these sub-particles called quarks:
up, down, charm, strange, top, bottom
. They do not exist alone. They are the particles of energy that give the neutrons and the protons their charge.

: A new way of looking at an atom through mathematics (
Devised our current atomic model called the
electron cloud
model. Electrons are not believed to revolve around the nucleus like planets but instead within a
that surrounds the nucleus.
Full transcript