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Democritus (460 BC - 370 BC)
He created the atomic theory in 400 BC. He stated that the atom was the smallest quantity of matter. His theory led to inspiring others. The man he learned all of the information from was named Lecuippus. -
John Dalton (1766 - 1844)
Dalton noted that oxygen and carbon could combine and make two separate compounds, He formed his atomic theory in an attempt to explain how and why elements would combine to make compounds. His atomic theory stated that elements consisted of tiny particles called atoms, and that all atoms of an element are identical. -
Dmitri Mendeleev (1834 - 1907)
From early in his career, he felt that there had to be some type of order to the elements, and he spent more than thirteen years of his life collecting data and assembling the concept that there was. He was in correspondence with scientists around the world in order to receive data that they had collected. He used their data along with his own data to arrange the elements according to their properties. By 1869, the Russian chemist had assembled detailed descriptions of more than 60 elements. -
Wilhelm Conrad Rontgen (1845 - 1923) (World History Event #1)
He observed, and recorded, the first X-rays. He was fiddling with his cathode ray generator and discovered an image projected far from the possible range of the cathode rays. The rays were generated at the point of contact of the cathode ray on the interior of the vacuum tube. They weren't deflected by magnetic fields and they penetrated all kinds of matter. He took an x-ray of his wife's hand a week afer his discovery. -
Joseph John "JJ" Thomson (1856 - 1940)
JJ Thomson discovered electrons in 1897. He discovered them using a series of experiments designed to study the nature of electric discharge in a high vacuum cathode-ray tube. He interpreted the deflection of rays by magnets and electrically charged plates as evidence of bodies much smaller than atoms. -
Karl Ferdinand Braun (1850 - 1918)
He invented the cathode ray tube (CRT), which is a specialized vacuum tube in which images are produced when an electron beam strikes a posphorescent surface. He introduced a CRT with fluorescent screen. It would emit a visible light when struck by a beam of electrons. -
Ernest Rutherford (1871 - 1937)
Ernest Rutherford discovered protons in 1911. He describes the atom as having a central positive nucleus surrounded by negative orbiting electrons and that the atom is mostly empty space. His gold foil experiement helped discover the proton. -
Erwin Schrodinger (1887 - 1961)
He built upon the thoughts of Bohr but took them in a new direction. He developed the probability function for the Hydrogen atom (and a few others). The probability function basically describes a cloud-like region where the electron is likely to be found. The electron-cloud model is basically an atom that has electrons around it existing in different "clouds" and on different energy levels. -
Neils Bohr (1885 - 1962)
In 1922, Neils Bohr explained the atomic structure of the atom as "successive orbital shells of electrons." He suggested that electrons couldn't move continiously in the atom but in precise steps. He said that electrons occupy specific energy levels. He predicted that the levels had limits to the number of electrons it could hold. -
John Crockoft and Ernest Walton (1987 - 1967; 1903 - 1995)
In 1932, when Cockcroft and Walton, in Rutherford's laboratory, built a machine that could shoot a beam of protons at very high speeds, they fired protons, like bullets, into metal targets. The collisions transformed some of the nuclei in the target atoms. Some of the atoms' mass was converted into energy. Thus, they split the atom for the very first time. -
James Chadwick (1891 - 1974)
In 1932, he discovered the neutron. He used alpha particles and discovered a neutral atomic particle with a mass close to a proton. -
Atomic Bomb Droppings - "Fat Man", "Little Boy" (August 6, 1945; August 9, 1945) World History Event #2
On August 6, 1945, the atomic bomb "Little Boy" was dropped on the Japanese city of Hiroshima. 3 days later, another bomb, "Fat Man" was dropped on another city named Nagasaki. These bombings ended World War II. -
Use of the Periodic Table of Elements (Present Day) World History Event #3
The periodic table, since developed in 1869 and added on to years after, is still being used today by scientists, as well as science teachers and their students. For example, if a person knows the main properties of each of the groups in the periodic table and how chemical properties vary within a group, he or she can predict the properties of any particular element.
