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460 BCE
Democritus
Democritus was born in Abdera around 460 BC. He created a theory that everything is composed of atoms. He also believed that atoms could not be changed and were indestructible. His atomic model was solid. He also believed that atoms differed in shape and size. He discovered this by continuously breaking a rock in half until the particles were microscopic. He determined that the rock didn’t just disappear so he created the atom. His atom model was called the Democritus model. -
400 BCE
Democritus
Democritus was born in Abrade around 460 BC. He made a theory that are made of atoms, which he said were physically invisible. He believed that atoms could not be changed and were indestructible. His atomic model was solid. He believed that atoms differed in shape and size. He discovered this by continuously breaking a rock in half until the particles were microscopic. He sensed the rock didn’t just disappear so he created the atom. His model of the atom is called the Democritus model. -
Period: 400 BCE to
History of Atomic Theory
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John Dalton
John Dalton was born on September 6, 1766 in Eaglesfield, England. By experimenting with gases, he discovered Modern Atomic Theory that says that matter is made up of atoms that are indivisible and indestructible. He also found that all atoms of an element are identical, atoms of different elements have different weights and chemical properties, and atoms of different elements combine to form compounds. This last claim in his theory is that atoms cannot be created or destroyed. -
John Dalton
John Dalton was born on September 6, 1766 in Eaglesfield, England. He was born to a Quaker family and he was color blind. Dalton founded that matter was made up of small individual particles. His Modern Atomic Theory states matter is made up of atoms that are indivisible and indestructible. He also found that all atoms are identical, atoms of different elements have different weights and chemical properties. His theory is that atoms cannot be created or destroyed. -
JJ Thompson
J.J. Thomson was born on December 18, 1856 in Chatham Hill, England. Thomson performed an experiment called the Cathode Ray Tube Experiment where he passed the rays through a vacuum and noticed that the ratio from electrical charge to mass of the particles was the same in every gas. This led him to his discovery that all matter is made up of particles called corpuscles, though now they are called electrons. His atomic model that he created is called the Thomson atomic model -
Cathode Ray Tube Experiment
J.J. Thomson created the the Cathode Ray Tube Experiment where he passed the rays through a vacuum and noticed that the ratio from electrical charge to mass of the particles was the same in every gas. This led him to his discovery that all matter is made up of particles called corpuscles, though now they are called electrons. -
J.J. Thomson
J.J. Thomson was born on December 18, 1856 in Cheetham Hill, England. Thomson performed the Cathode Ray Tube Experiment where he passed the rays through a vacuum and noticed that the ratio from electrical charge to mass of the particles was the same in every gas. He discovered that all matter is made up of particles now called electrons. His atomic modeis called the Thomson atomic model which shows how electrons are inside atoms. He received a Nobel Prize for Physics in 1906. -
Oil Drop Experiment
He replaced the water with oil, since it evaporated too fast, in 1910 because the oil did not evaporate as quickly as the water did. In his famous oil-drop experiment, he placed 2 electrically charged drops of oil between 2 electrodes. Then he balanced the forces by using a mechanical equilibrium that determined the charge, which was within 1% of the current accepted value. He is credited for discovering the value of the charge of an electron. -
Robert Millikan
Robert Millikan was born on March 22, 1868 in Morrison Illinois. In his famous oil-drop experiment, he placed 2 electrically charged drops of oil between 2 electrodes. Then he balanced the forces by using a mechanical equilibrium that determined the charge, which was within 1% of the current accepted value. He is credited for discovering the value of the charge of an electron. -
Ernest Rutherford
Ernest Rutherford was born on August 30, 1871 in Spring Grove, New Zealand. Rutherford conducted the Gold Foil experiment where he shot a beam of alpha particles at a thin sheet of gold foil, and he found that some of the particles were deflected. He was the first person to discover that atoms have a small nucleus surrounded by empty space, encircled by electrons. This model he created is known as the Rutherford model of the atom. -
Gold Foil Experiment
To come about finding this discovery, Ernest Rutherford conducted the Gold Foil experiment where he shot a beam of alpha particles at a thin sheet of gold foil, and he found that some of the particles were deflected. This brought about his conclusion that a nucleus was causing the deflections. -
Neils Bohr
Born on October 7, 1885 in Copenhagen, Denmark, Neils Bohr was a Danish Physicist who made astonishing contributions to the understanding of atomic structure and quantum theory. Bohr created the Bohr Model of the atom in which he described that energy levels of electrons are discrete and that the electrons revolve around the atomic nucleus but can jump from one energy level to another. -
Neils Bohr
Born on October 7, 1885 in Copenhagen, Denmark, Neils Bohr was a Danish Physicist who made astonishing contributions to the understanding of atomic structure and quantum theory. Bohr created the Bohr Model of the atom in which he described that energy levels of electrons are discrete and that the electrons revolve around the atomic nucleus but can jump from one energy level to another. -
Erwin Schrodinger
Erwin Schrodinger was born on August 12, 1887 and was born in Vienna, Austria. Schrodinger developed an “Electron Cloud Model” in 1926 which consisted of a dense nucleus surrounded by a cloud of electrons at various orbital levels. Using mathematics Schrodinger and Werner Heinsburg determined regions in which electrons would most likely be found using mathematics. -
Erwin Schrodinger
Erwin Schrodinger was born on August 12, 1887 in Vienna, Austria. Schrodinger developed an “Electron Cloud Model” in 1926 which consisted of a dense nucleus surrounded by a cloud of electrons at various orbital levels. Using mathematics Schrodinger and Werner Heinsburg determined regions in which electrons would most likely be found using mathematics. Schrodinger was a Nobel-Prize winner for his amazing contributions to science. -
James Chadwick
James Chadwick was born on October 20, 1891 in Bollington, Cheshire, England. Chadwick is well known for his discovery of the neutron in 1932. When World War One broke out the German government imprisoned Chadwick for four years. He constructed experiments while imprisoned and discovered the neutron in 1932 and found it was a new particle and different than a proton. His discoveries led to the further understanding of nuclear fission and the ultimate creation of the atomic bomb. -
James Chadwick
Chadwick was born on October 20, 1891 in Bollington, Cheshire, England. He is well known for his discovery of the neutron. His discoveries helped understand nuclear fission and the creation of atomic bomb. His intentions were to study beta radiation but as World War One broke out the German government imprisoned Chadwick for four years. He constructed experiments while imprisoned and when the war was over he returned to England to perform further experiments under Ernest Rutherford.
