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100
Alchemists
500 BCE, Alchemy is based on water, fire, earth, and air as matter. Alchemists would study the deconstruction of objects into these types of matter. This deconstruction contributed to the creation of the periodic table. -
200
Democritus of Adbera
400 BCE, Democritus created the first atomic model. It was simply a round sphere with no electrons, protons, or neutrons. He first proposed the existence of an ultimate particle, and he used the word "atomos" to describe this particle. -
300
Aritsotle
300 BCE, He proposed that all matter consisted of four elements: earth, air, water, and fire, and that all matter consisted of four qualitlies: dryness, hotness, coldness, and wetness, and that fire was dry and hot and water was cold and wet. -
Period: 500 to
Atomic Theory Timeline Project
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Jan 1, 1558
Giordano Bruno
1558-1600, Bruno believed that God was present in every atom. This meant that transubstantiation was impossible, which went against the very fibers of the Catholic church he was raised in. -
Robert Boyle
1627- 1691, He proposed that elements are composed of 'corpuscles' of various types and sizes that are able to organize themselves into groups that represent different chemical substances. He also was able to distinguish between a mixture and a compound. He stressed organization of atoms and is sometimes called the Father of Chemistry for his extensive work on materials. -
Isaac Newton
1704, He proposed a mechanical universe where small solid masses were in motion. In summary, he believed that there were little tiny pieces of mass that were swimming everywhere. He began to understand that atoms or particles move and are not stationar -
Banjamin Franklin
1732, He proposed that electricity contained negative and positive charges. He discovered that there was an electrical fluid in a long glass tube that would flow from one point to the other, therefore Franklin established the negative and positive charges that contributed to the understanding of the atom. -
Antoine Lavoisier
He stated the Law of Conservation, which law states that matter cannot be made or destroyed. He also hinted at the rearrangement of matter in reactions, saying matter rearranged, but never disappeared. He began the conversation on what an atom was exactly. -
John Dalton
He proposed an atomic theory that stated all matter is composed of small particles called atoms and that all atoms of the same element are identical, while atoms of different elements have a different size and mass. He also proposed that chemical compounds are composed of atoms in defined ratios, chemical reactions result in a rearrangement of atoms, and atoms cannot be subdivided or created/destroyed. His atomic model was just a spherical atom. -
Michael Faraday
He studied the effect of electricity on solutions, coined the term "electrolysis" as a splitting of molecules with electricity, and developed the laws of electrolysis. -
Dmitri Mendeleev
He arranged elements into 7 groups with similar properties. He discovered that the properties of elements were periodic functions of the their atomic weights. This became known as the Periodic Law. -
William Crookes
He discovered that cathode rays had the following properties: travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass. -
Wilhelm Roentegn
Using a CRT, he observed that nearby chemicals glowed. Further experiments found very penetrating rays coming from the CRT that were not deflected by a magnetic field. He named them "X-rays", which are used in various other experiments that furthered the atomic model. -
Henry Becquerel
While studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very penetrating rays. -
Joseph John Thomson
He determined the charge to mass ratio of an electron. He used a cathode ray tube to determine that the charge to mass ratio of an electron to be 1.759 x 10 8 coulombs/gram. Thomson also developed the plum pudding model of the atom. -
Marie & Pierre Curie
They studied uranium and thorium and called their spontaneous decay process "radioactivity". She and her husband Pierre also discovered the radioactive elements polonium and radium. Their knowledge of spontaneous decay was used in experiments to further the atomic model. -
Frederick Soddy
He observed spontaneous disintegration of radioactive elements into variants he called "isotopes" or totally new elements, discovered "half-life", made initial calculations on energy released during decay. -
Max Planck
He used the idea of quanta (discrete units of energy) to explain hot glowing matter. -
Hantaro Nagaoka
He postulated a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle. -
Albert Einstein
He published the famous equation E=mc2. -
Robert Millikan
Millikan’s oil drop experiment determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron. -
Ernest Rutherford
Rutherford discovered the nucleus. When launching particles at a gold sheet, the particles would usually bounce through but a few times the particle would be deflected, and therefore there was a small positively charged nucleus that would deflect the particles. -
Henry Moseley
Using x-ray tubes, Moseley determined the charges on the nuclei of most atoms. He wrote"The atomic number of an element is equal to the number of protons in the nucleus". This work was used to reorganize the periodic table based upon atomic number instead of atomic mass. -
Francis William Aston
He discovered the existence of isotopes through the use of a mass spectrograph. -
Niels Bohr
Bohr stated that electrons jump from orbit to orbit. He described the jumping as giving off quantum light, and he used quantum theory to explain his theories. -
Louis deBroglie
De Broglie discovered the "wave nature" of electrons. He introduced his theory of particle-wave duality in 1924. He suggested that particles can behave like waves, and waves (radiation) can behave like particles. -
Werner Heisenberg
Heisenberg described atoms by means of formula connected to the frequencies of spectral lines. Proposed Principle of Indeterminancy - you can not know both the position and velocity of a particle. -
Erwin Schrödinger
Schrödinger viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom. -
James Chadwick
He discovered neutrons.They differed from alpha rays because they repelled considerable electrical forces that are in the nucleus of many heavy atoms. A neutron can then penetrate and split the nuclei of most elements.This advancement allowed for the fission of uranium, and the creation of very powerful bombs. -
Glenn SeaBorg
1941 - 1951, SeaBorg synthesized 6 transuranium elements and suggested a change in the layout of the periodic table. Which has affected modern day chemistry in regard to the periodic table. -
Enrico Fermi
Fermi conducted the first controlled chain reaction releasing energy from the atom’s nucleus. He created the world’s first nuclear reactor, and is often called the “architect of the atom bomb.”