jay.santodomingo.atomichistory.fall.2009

He was an ancient Greek philosopher born in Greece. Democritus did not originate   the atomic theory, he learned it from its founder, Leucippus. Democritus stated that there are atoms and the void (free space) and that everything is made up of atoms, atoms too small to be seen or diminished. With this as a basis to the physical world, Democritus could explain all changes in the world as changes in motion of the atoms, or changes in the way that they were packed together.
 * 450-Prior **

440BC Little is known about him, but that he was the founder of atomism. He came up with the theory that the universe consists of two different elements, which he called the solid and void. Both the void and the solid atoms within it are thought to be infinite, and between them to constitute the elements of everything. More is known about his predecessor Democritus. Born in Greece about 384-322 BC. He believed that nature consisted of four elements earth, air, fire, and water. Aristotle is said to have written 150 philosophical papers that range from biology and physics to morals to aesthetics to politics. A fun fact is that he tutored Alexander the Great.

1700-1800 ** 1733-1804 He is best known for his discovery of oxygen, he was able to isolate it and identify it. He produced it on August 1, 1774, by heating red mercuric oxide, and then it was clear that air was not an element. Priestley was also the first to identify plant respiration and photosynthesis.

1711**-**1787 Boscovich’s atomic theory has three parts, he based them off of Newton and Gottfried Wilhelm Leibniz. (1) Material permanence without spatial extension: Quasi-material point-centers of action are substituted for the rigid finite units of matter of earlier atomists. (2) Spatial relations without absolute space: Internal spatial coordinates (the distances between the two members of pairs of //puncta//) are used instead of external coordinates. (3) Kinematic action without Newtonian forces: In modern dimensional terms, Boscovich's theory is kinematic rather than dynamical. It uses only two-dimensional quantities (length and time) rather than the three (mass, length, and time) used by Newton. Since all particles are identical, the number of particles in a system, which is an integral pure number obtained by counting, is employed in place of Newtonian mass.

1642-1727 Newton's Laws of Motion: (1)An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force. This law is often called "the law of inertia".

( 2)Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).   (3)For every action there is an equal and opposite re-action.

** 1800-1875 ** 1766-1844 His Atomic Theory: 1) All matter is made of atoms. Atoms are indivisible and indestructible. 2) All atoms of a given element are identical in mass and properties 3) Compounds are formed by a combination of two or more different kinds of atoms. 4) A chemical reaction is a rearrangement of atoms.

1834-1907 His Periodic Table was formed on the basis of arranging the elements in ascending order of atomic weight and grouping them by similarity of properties. He predicted the existence and properties of new elements and pointed out accepted atomic weights that were in error. He predicted the discoveries of gallium, scandium, and germanium and left spots for them in the table.

1779-1848 In dealing with so many elements in so many compounds he created a simple and logical system of symbols; H, O, C, Ca, Cl, and so forth which is basically the same system we use today. He also introduced the present system of chemical formulation. Berzelius discovered the elements cerium, selenium, and thorium.

** 1875-1900 ** 1852-1908 The material Becquerel worked with was a double sulfate of uranium and potassium which he exposed to sunlight and placed on photographic plates wrapped in black paper. When developed, the plates revealed an image of the uranium crystals. Becquerel determined that the phosphorescent substance emits radiation which penetrates paper. This meant that the uranium emitted radiation without an external source of energy such as the sun. He was awarded the 1903 Nobel Prize for his discoveries.

1845-1923  He was experimenting with electric current flow in a partially evacuated glass tube and observed that a nearby piece of barium gave off light when the tube was in operation. He theorized that when the cathode rays struck the glass wall of the tube, some unknown radiation was formed that traveled across the room, struck the chemical, and caused the fluorescence. He investigated it further and revealed that paper, wood, and aluminum are transparent to this new form of radiation. He called it an x-ray. The first x-ray was of his wife’s hand.

1856-1940 He discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube. In 1904 he suggested a model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces. It is known as the plum pudding model.

** 1900-1915 **



In 1913, Bohr published a theory about the structure of the atom based on an earlier theory of Rutherford's. Rutherford had shown that the atom consisted of a positively charged nucleus, with negatively charged electrons in orbit around it. Bohr expanded upon this theory by proposing that electrons travel only in certain larger orbits. He suggested that the outer orbits could hold more electrons than the inner ones, and that these outer orbits determine the atom's chemical properties. For his research he received the Nobel Prize in physics in 1922.



 1867-1934 Curie studied uranium radiations, and piezoelectric techniques devised by her husband to carefully measure the radiations in pitchblende, an ore containing uranium. When she found that the radiations from the ore were more intense than those from uranium she realized that unknown elements were even more radioactive than uranium were present. Marie Curie was the first to use the term radioactive to describe elements that give off radiations as their nuclei break down. Pierre Curie ended his own work on magnetism to join his wife's research, and the Curies announced their discovery of two new elements radium and polonium. Marie Curie was the first female recipient of the Nobel Prize.

1868-1953 In 1909 Millikan began a series of experiments to determine the electric charge carried by a single electron. He began by measuring the course of charged water droplets in an electrical field. The results suggested that the charge on the droplets is an electric charge, but the experiment was not accurate enough to be convincing. He obtained more precise results in 1910 with his famous oil-drop experiment in which he replaced water with oil.



1871-1937 He discovered alpha and beta rays, which set forth the laws of radioactive decay, and identified alpha particles as helium nuclei. Most importantly he discovered the nuclear structure of the atom by observing experiments done in Rutherford's laboratory which showed that when alpha particles are fired into gas atoms, a few are violently deflected, which implies a dense, positively charged central region containing most of the atomic mass. He also discovered half-life of radioactive elements and applied this to studies of age determination of rocks, by measuring the decay period of radium to lead.

** 1915-1950 ** 1891-1974 He made a fundamental discovery in the domain of nuclear science where he proved the existence of neutrons. Chadwick's discovery was advanced experimental work for all scientists, and in his experiments since neutrons have no electrical charge, any neutrons fired from a source has the ability to go through deep layers of materials. He also helped to work on the atomic bomb in Manhattan. 

1901-1976 He tried to measure an electron's properties by hitting it with gamma rays which would alter the electron's behavior. He found out that you could measure the position of an electron or you could measure its momentum, but the more precisely you measure one property, the more you throw the other off. He used this information to make an equation using Planck's constant, and called it the uncertainty principle. Many scientists resisted this idea but, it eventually became accepted as a fundamental law of nature. Heisenberg was a German scientist during World War II and worked on the German atomic bomb for five years.

1887-1961

He was an Austrian physicist who invented wave mechanics in 1926. Wave mechanics are the mathematically described behavior of electrons and atoms.



**__ History __**

__450-Prior__ - The battle at Thermopylae __1700-1800__ - American Revolution __1800-1875__ - U.S. Civil War __1875-1900__ - __1900-1915__ - __1915-1950__ - World War I - world War II