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Democritus
Democritus formulated what, is thought to be the first atomic theory. He hypothesized that all matter (including space and time) is composed of tiny indestructible units, called atoms. His theory is that matter could not be divided into smaller and smaller pieces forever; eventually the smallest possible piece would be obtained. This piece would be indivisible. -
Antoine Lavioser
Antoine Lavioser was the first person to make good use of the balance. He began the conversation on what an atom was exactly. He proposed the Combustion Theory which was based on sound mass measurements. He also named oxygen. -
John Dalton
Dalton's theory was based on the premise that the atoms of different elements could be distinguished by differences in their weights. His theory based upon:
1. An element is composed of tiny, indestructible, indivisible particles called atoms.
2. All atoms of the same elements are identical, and have the same properties.
3. Atoms of the same elements combine to make compounds.
4. Compounds contain atoms in small whole number ratios.
5. A chemical reaction is a rearrangement of atoms. -
E. Goldstein Discovered Canal Rays
E. Goldstein discovered canal rays, which have a positive charge equal to an electron. -
Wilhelm Roentgen
Wilhelm Roentgen discovered x-rays. -
J.J. Thomson
J.J. Thomson discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube, an area being investigated by numerous scientists at the time. interpreted the deflection of the rays by electrically charged plates and magnets as evidence of "bodies much smaller than atoms" that he calculated as having a very large value for the charge-to-mass ratio. -
Marie Curie
Marie Curie discovered radium and polonium and coined the term radioactivity after studying the decay process of uranium and thorium in 1898. She discovered the radioactive elements polonium and radium in the pure state in 1902. -
Max Planck
Max Planch contributed to the Quantum Theory. He proposed that energy is radiated in every minute and discrete quantized amounts or packets, rather than in a continuous unbroken wave. Planck called the packets of energy quanta and he was able to determine that the energy of each quantum is equal to the frequency of the radiation multiplied by a universal constant that he derived, now known as Planck's constant. His constant has become one of the basic constants of physics. -
Albert Einstein
Albert Einstein became famous for the theory of relativity, which laid the basis for the release of atomic energy. The modern atomic theory is also known as the quantum theory, he contributed to the quantum theory the most by being against it, which caused Neil Bohr to create more models and explanations for it. Also, he Published the famous equation E=mc 2. -
Hans Geiger.
Hans Geiger invented a device that could detect alpha particles. -
Robert Millikan
Robert Millikan determined the unit charge of the electron in 1909 with his oil drop experiment. As a result, it allowed for the calculation of the mass of the electron and the positively charged atoms. He proved Thomson's hypothesis that the mass of an electron is at least 1000 times smaller than the smallest atom after he completed his oil drop experiment. -
Ernest Rutherford
Ernest Rutherford published his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons. He came to this conclusion following the results of his famous gold foil experiment. The experiment involved the firing of radioactive particles through minutely thin metal foils and detecting them using screens coated with zinc sulfide. This led to him thinking that most of the atom is made up of empty space. -
Niels Bohr
Niels Bohr applied the quantum theory to Rutherford's atomic structure by assuming that electrons travel in stationary orbits defined by their angular momentum. As a result, it led to the calculation of possible energy levels for these orbits and the postulation that the emission of light occurs when an electron moves into a lower energy orbit. In 1915, he proposed the Bohr Model. -
Arnold Sommerfeld
Arnold Sommerfield improved the Bohr Model. He assumed that the orbits of electrons doesn't have to be spherical but can also be elliptic. The electrons can move only on some, allowed ellipses. He coined a second l number which was called the secondary quantum number or the azimuthal quantum number. The number defined the shape, the oblateness of an orbit. He also discovered that the orbits don't have to lay in the same plane. They can be oriented in space on some defined directions. -
Louis De Broglie
Louis De Broglie proposed in 1924 that particles can behave like waves, and waves (radiation) can behave like particles. His ideas were a basis for developing the wave mechanics theory. This theory has greatly improved our knowledge of the physical nature on the atomic scale. He received the Nobel Prize for Physics on his wave nature of electrons discovery in 1929. -
Erwin Schrödinger
Erwin Schrödinger formulated in 1926 a wave-equation that accurately gave the energy levels of atoms. He used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model of the atom. -
Werner Heisenberg
Werner Heisenberg calculated the behavior of electrons, and subatomic particles that also make up an atom.His discovery helped clarify the modern view of the atom because scientists can compare the actually few numbers of atoms there are, by their movements of electrons, and how many electrons an atom contains. He included quantum mechanics, the branch of mechanics, based on quantum theory, used for interpretating the behavior of elementary particles and atoms. -
Cockcroft/Walton
Cockcroft/Walton created the first nuclear reaction utilizing particle accelerators, producing alpha particles. -
Paul Dirac
Paul Dirac proposed the existence of anti-particles. -
James Chadwick
James Chadwick made a fundamental discovery in the doorman of nuclear science. He established that an atomic number is determined by the numbers of protons in an atom, and discovered protons. -
Enrico Fermi
Enrico Fermi created the first man-made nuclear reactor. -
Atomic Bomb Dropped on Japan to End WW2
The Atomic Bomb from Cockcroft and Walton was dropped on Japan to end the World War 2 in 1945
