Atomic Theory - Essay

1531 Words Nov 7th, 2011 7 Pages
Atomic theory is the idea that matter is made up of small particles made of atoms. The atomic theory first had 5 points which were stated by John Dalton who came up with it. The first one was that all elements were made up of small units called atoms. The second one was that all atoms of a given element are identical to each other. Third, all the atoms were different from all the other atoms. Fourth, atoms of different elements combined together in equal numbers to form compounds. Fifth and final, atoms cannot be broken down, created or divided. John Dalton was a chemist in the early 19th century and his work was focused on the behavior and properties of gases. He used his work on gases to come up with his law of proportions which was …show more content…
1869 Dmitri Mendeleev Arranged elements into 7 groups with similar properties. He discovered that the properties of elements”were periodic functions of their atomic weights". This became known as the Periodic Law.
1873 James Clerk Maxwell Proposed electric and magnetic fields filled the void.
1879 Sir William Crookes Discovered 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.
1886 E. Goldstein Used a CRT to study "canal rays" which had electrical and magnetic properties opposite of an electron.
1894 G.J. Stoney Proposed that electricity was made of discrete negative particles he called electrons ". (Link to info on electrons)
1895 Wilhelm Roentgen 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".
1896 Henri Becquerel While studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very penetrating rays.
1897 J.J. Thomson Used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 10 8 coulombs/gram.
1897 J.J. Thomson Studied "canal

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