1800-1900

=__ ** Atomic Theory: 1800-1900 ** __=


 * John Dalton || [[image:reich-chemistry:johndalton.jpg width="238" height="315" caption="John Dalton"]] ||

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.

Mendeleev || ||
 * Dimitri

1834-1907 His Periodic Table was formed on the basis of arranging the elements in ascending order of atomic weight, 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.


 * Berzelius || [[image:reich-chemistry:berzelius.jpg width="220" height="246" caption="Berzelius"]] ||

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.

Becquerel || ||
 * Henry

1852-1908 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.

Roentgen || ||
 * Wilhelm C.

1845-1923  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, called an x-ray.

Thomson || ||
 * Joseph

1856-1940 He discovered the electron in a series of experiments designed to study the nature of electric discharge. 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.